SOP manual rev B - New Jersey QRP Club

SOP manual rev B - New Jersey QRP Club
New Jersey
SOP Receiver Kit
A “universal” CW receiver for 80m and 40m operation.
Easy to modify for use on other bands. Direct conversion for simplicity and performance. Low current drain
from 9V-12V battery is perfect for portable operation.
Open pc board layout - perfect for novice homebrewers,
great for experimenting. Add-on accessories: FreqMite
audio frequency dial, homebrew copper-clad enclosure,
all controls, knobs & jacks.
Brought to you by the New Jersey QRP Club
SOP Receiver Assembly
Manual, rev B
About this manual ...
This manual actually consists of five separate manuals combined
into a single and convenient reference manual for the NJQRP SOP
SECTION 1: SOP Receiver -- Covers theory of operation, assembly,
debug and operation of the base SOP Receiver kit ................ page 3
SECTION 2: “FreqMite” Audio Frequency Annunciator -- Covers the
assembly and operation of the optional “audio frequency dial”
components kit ..................................................................... page 22
SECTION 3: “Homebrew Enclosure” -- Covers assembly and
finishing of the optional pcb enclosure kit ............................ page 26
SECTION 4: “Controls & Hardware” -- Covers the assembly of the
optional kit providing components that are external to the pc board:
potentiometers and jacks ..................................................... page 39
SECTION 5: Test and Measurement Circuits -- Provides schematics
and guidance for usage of various circuits useful in constructing and
debugging the SOP Receiver .............................................. page 41
Copyright 2000, George Heron, N2APB and the New Jersey QRP Club.
All rights reserved.
Edited and published by N2APB, using Pagemaker v6.
Printed by Sir Speedy Printing in Baltimore, Maryland.
SOP Receiver Assembly Manual, rev B
SOP Receiver Kit
Assembly Manual
The SOP is a basic “Seat Of the Pants” receiver designed by veteran
elmer Joe Everhart, N2CX, and is being kitted and sold by the NJQRP
Club. This kit is a very flexible and inexpensive direct conversion CW
receiver for 40m or 80m. Providing better quality than a single-chip
receiver, yet not as complex as a superhet, the SOP’s straightforward
design and construction is ideal for newcomers to the homebrewing
scene as well as for experienced QRP builders.
tion and small size.
Thanks for purchasing the SOP Receiver
Kit from the NJQRP Club. This section
of the manual provides a basic technical
overview of the design and operation, and
details the assembly required to make it a
functional receiver in your shack.
It uses a simple direct conversion technique and is well-suited for experimentation. Though designed originally as a
companion to the NJQRP Fireball-40
transmitter, it is a “natural” to team up
with any simple QRP transmitter. Another use is that of band monitoring. The
SOP provides an elegant way to listen to
a band wherever you might be.
The SOP (Seat-Of-the-Pants) is intended
as a utility CW receiver, useful in the
shack to complement some of the simple
transmitter projects available today (Tuna
Tin 2, Fireball 40, etc.); or for use in the
field because of its low power consump-
The SOP incorporates an audio low pass
filter to minimize off-frequency interference but by design is not so selective that
SOP Receiver Assembly Manual, rev B
nearby signals cannot be heard. While
superheterodyne receivers offer better
performance, the SOP’s simplicity makes
it easier to tune up on anywhere in the
HF spectrum for CW (or SSB) reception.
An important concept to keep in mind is
that the SOP is an experimenter’s receiver. The building blocks used in the
design are simple and straightforward,
providing a clear functional representation of a relatively generic receiver platform. Thus the SOP is a perfect receiver
platform with which to try out new ideas.
The printed circuit board for the SOP is
similarly generous in size to provide novice fingers ample space to assemble and
for oscilloscope probes and extra components to be connected. The functional
blocks of the design are arranged in a
manner to allow easy modification and
substitution of components. In fact, one
could easily provide little “daughter
boards” to sit directly above any particular module to replace or augment its function. For example, if a better audio filter
is desired (more poles, different rolloff
characteristics, etc), one could create a 1”
x 1” board containing the improved filter
and suspend it above the stock filter on
the middle-right end of the board,
jumpering the input and output signals
down to the original board. Great flexibility is provided in the SOP in this manner.
The SOP Receiver was designed for flexibility. Again, with the basic no-frills
component construction, the design can
be easily modified for use on other bands.
Application notes will be available in the
near future describing the changes necessary to put the receiver on any HF ham
band, from 10m to 160m.
The SOP is not necessarily the highestperforming receiver you can find. But for
its low cost, it will provide you many
hours of quality service as a flexible re-
ceiver in the shack, as well as being a platform for you to modify and improve on
as your needs and skills develop.
In the process of assembling your SOP
and in modifying it to suit your particular needs, you will gain a better understanding of the principles of receivers,
including oscillators, mixers, RF and audio amplification, and audio filtering.
We hope you enjoy your SOP Receiver
Here is a brief listing of the SOP
receiver’s specifications. See Figure 1 for
a corresponding block diagram.
1) The SOP is a “universal” HF CW
- Low current drain; able to operate from
9V battery or 12V source;
- Small size enables use as custom rig or
as standalone portable monitor receiver;
- Jumper selectable operation on 80m or
- Can be set up on any other HF band
(30m-10m) with few component changes;
- No critical assembly or alignment required;
- Tailorable for advanced homebrewers extra pcb space provided for experimentation;
- No odd-ball crystals, variable capacitors or other components;
- Plug and play design ideal for beginners or advanced homebrewers;
- Solid repeatable design;
- Open layout on PC board simplifies
2) The RF Amp
- Provides front end gain and selectivity;
- Very stable grounded gate FET design;
- Provides adequate gain and enhances
noise figure on higher HF bands;
- Can be tailored to any HF band via parallel inductor or capacitor (pcb space pro-
SOP Receiver Assembly Manual, rev B
3) The Local Oscillator
- Simple, trouble-free VXO design provides variable tuning control;
- Uses ceramic resonator for 80m & 40m
operation, easily placed anywhere on
band with alternate resonator/crystal;
- Tuning range is > 50 KHz on 80m, and
> 100 KHz on 40m, ensuring coverage
of the standard QRP operating frequencies on each band;
- Tuning range can be limited simply by
changing padding resistors;
- Can use other crystal or resonator to
cover any HF band on 80m to 10m;
- Output tank is shielded inductor - eliminates fragile trimmer capacitors;
- Output tank tailored to any HF band via
parallel inductor or capacitor (pcb space
- Varactor tuning via potentiometer eliminates need for big, expensive variable
4) The LO buffer
- Stable, repeatable design provides highlevel drive to mixer stage for improved
- No adjustments;
- Broadband performance.
5) The Mixer
- Single-chip, passive double balanced
mixer (dbm);
- No diode matching or toroid winding,
yet all the benefits of discrete dbm performance;
- Better performance in crowded HF
bands than single IC mixers;
- Simple wide-band termination on output helps reject interference.
6) The Audio Stage
- Low noise bipolar amplifier provides
amplification and filtering;
- Integrated circuit audio filter helps with
cw reception;
- Low pass filter peaked for CW tones;
- No adjustments;
- No ringing or ear fatigue;
- Filters out high frequency “monkey
7) The Audio Muting and Amplifier
- Proven muting design quiets receiver
audio during transmit via keyline signal
from transmitter;
- Bypass resistor on muting switch allows
operator to hear sidetone of the transmitted signal;
- Allows verification of transmit frequency offset;
- Proven LM386 amplifier features high
frequency hiss rejection;
- Anti motorboat components give clean
audio output;
- Sufficient output for low impedance
headphones or small speaker.
Figure 2 shows the SOP’s schematic.
RF Pre-Amp
The SOP RF amplifier is a single-stage
common-gate FET stage that provides
front-end gain and selectivity for the receiver. The antenna input is link-coupled
to a tuned circuit to provide impedance
matching which preserves circuit Q while
efficiently coupling receive energy. Resonance at 7 MHz is achieved by use of a
150 pF trimmer capacitor, allowing “onfrequency” tuneup. The transformer
winding instructions can be scaled to
other amateur bands as well. Energy from
the tank is coupled to the FET source via
a two-turn tap. Not that both the input
link and output tap are 2 turns providing
identical input and output matching. The
input impedance of the grounded gate
amplifier is in the range of 50 to 100 ohms
so a reasonable match is achieved.
Source resistor R11 is used to provide a
negative gate bias to stabilize FET operation with a source current of several
milliamperes. The FET would probably
give more gain without the resistor, but
bias current would vary widely with de-
SOP Receiver Assembly Manual, rev B
ADE-1 dbm.
More crunch- ~20dB gain
proof than ‘602
4-pole Low
Pass Filter
LM 358
Stable pot-tuned
VXO with varactor
and resonator
2-stage buffer/amp
provides high
injection levels to
SA-612 based Local Osc
80m or doubled to 40m
Optional components easily
added for 30m thru 10m
Keyline mutes
Rx audio during Tx
(Mute) Bypass resistor
provides sidetone
LM 386
Audio amp
to drive ‘phones
or small speaker
SOP Receiver Assembly Manual, rev B
RF pre-amp
Audio Frequency Annunciation (optional)
“Freq-Mite” from Small Wonder Labs
announces operating frequency in Morse
code through receiver headphones.
Figure 1 - SOP Receiver Block Diagram
Space for
optional T-R
switch parts
vice-to-device tolerances. Gain stability
is more important than raw gain. Capacitor C15 provides a low-impedance bypass
across the R11 to prevent signal loss. The
common gate configuration provides a
small voltage gain with a low noise figure. The low noise is not too important at
the low end of the HF spectrum but will
aid ultimate receiver sensitivity on 20
meters and higher. An additional advantage of the common gate stage is that it is
quite stable and repeatable, thus requiring no neutralization or tricky adjustments.
Output selectivity and matching are
achieved via a common 10.7 MHz IF
transformer. It is resonated on 30 meters
and below by means of an external capacitor. On 20m and above, an external
capacitor and inductor do the job. Link
coupling steps down the high FET drain
impedance to the 50 ohm level required
by the ADE-1 balanced mixer. Tuning
adjustment is done by the variable inductance of the shielded transformer. Tuning is rather broad since the transformer
is heavily loaded by the following double
balanced mixer.
One of the most important areas of the
SOP is the mixer. A Mini-Circuits ADE1 double-balanced diode mixer is used.
This device is a surface mount packaged
equivalent of two small toroid transformers surrounding a ring of four diodes. It
provides good sensitivity while giving
much less audio rectification than the
more common NE602 Gilbert cell mixer
used in other direct-conversion receivers.
(The NE602 has been recently been superseded by the SA612 so from here on
out we will use the latter part number.)
R12 and C18 provide a wide-band termination to the ADE-1 mixer.
The Local Oscillator
The SOP uses an SA612 to provide the
local oscillator signal for the mixer. This
device incorporates both an oscillator and
a mixer in an 8-pin package — this dual
functionality is used to good advantage.
The “stock” SOP uses a 3.58 MHz ceramic resonator in a voltage controlled
oscillator to tune a portion of the 80 meter
band. The resonator has a lower Q than
that of a quartz crystal so it can be tuned
over a wider range while still being more
stable than an LC circuit. The fundamental oscillator output is used for 80 meter
operation. However if the oscillator signal is fed to the SA612 mixer section, it
is doubled in frequency to 40 meters. A
tuned circuit on the SA612 output minimizes 80 meter feedthrough. The receiver
can then be used on 40 meters by retuning the RF amplifier to that band.
This “trick” works well for 80 and 40
meters because of the inexpensive resonator. Unfortunately there are no standard
units available on other ham bands. However the SA612 can be set on other bands
by using quartz crystals in place of the
resonator. Tuning range can be enhanced
by using the “super VXO” techniques of
adding a series inductance and paralleling multiple crystals. Naturally the RF
amplifier must be retuned to the band of
interest. Application notes will soon be
made available showing how to effectively modify the basic 80m/40m SOP for
use on other bands.
The Local Oscillator is tuned by providing a variable DC voltage to a varactor
diode. The TUNE potentiometer provides
a portion of the regulated 6V DC level
coming from the 3-terminal voltage regulator U2. C16 and R10 bypass the DC
control signal to keep RF from getting
into the tuning components. When
varactor diode D3 sees a range of DC bias
voltage applied, its characteristic capacitance changes and adds to the total capacitance in the Y1 resonator circuit. This
varying capacitance “bends” the effective
frequency of the oscillator, providing the
SOP Receiver Assembly Manual, rev B
range of frequencies under control of the
The TUNE potentiometer is padded by a
resistor on each end. R7 and R8 can be a
jumper wire (i.e., zero ohms) to provide
the widest swing of DC control voltage,
and thus the widest swing of frequencies
from the oscillator. However this might
be too course an adjustment for some, so
a smaller tuning range can be forced by
placing actual in position at R7 and R8,
thus providing a smaller range of control
voltage for the same 300-degree turn of
the pot. This will have the effect of providing “bandspread-like” operation and
give the operator finer tuning control,
making it easier to tune closely-spaced
LO Buffer
The Local Oscillator Buffer is comprised
of the Q1 and Q2 stages immediately following the LO. Transistor Q1 is configured as an emitter follower to serve as a
high impedance buffer to minimize loading of the LO. Transistor Q2 is a common emitter amplifier with a wide-band
transformer to provide a low impedance
output (50-ohms) to drive the mixer stage.
By constructing T1 as a trifilar-wound
toroid transformer, we have an easy way
to achieve the wide-band impedance
transformation. R30, C10 and C37
decouple the buffer amplifier from the rest
of the circuits on the +V power line and
thus reduce the chance for feedback to
and from the power bus. (Direct-conversion receivers are very sensitive to crosscoupling through common power bus
Audio Gain
The ADE-1 audio output is boosted by a
low-noise 2N3565 transistor amplifier.
As in all direct conversion receivers most
of the gain is produced at audio frequencies. The mixer output is carefully filtered
by C36 to prevent RF feed-through. If you
don’t do this, strong AM signals will be
rectified in the audio amplifier! Again,
DC power to the audio amp is carefully
filtered by R19 and C34 to minimize feedback from other stages.
Low Pass Filter
A low-Q low pass filter is peaked in the
700-800 Hz area to give some audio selectivity but mainly to filter out off-frequency signals. This design originated
with Wes Hayward some years ago and
has been detailed in a number of publications and articles. Probably the most common reference is the ARRL “Solid State
Design for the Radio Amateur” by Hayward and DeMaw.
This unity gain amplifier and filter is direct-coupled — the same voltage appears
at R15/R16 junction, and at the op amp
output pins 1 and 7. C22 and C25 are
NPO-type capacitors for good frequency
stability of the filter. C23 and C25 are
also important for frequency stability, but
here we use mylar capacitors for a cost
effective solution.
Muting of the receiver is required during
“key down” times in order to keep the
very strong signal from blasting out the
audio amp output stage when the local
transmitter is keyed. This clever muting
circuit, borrowed from Hayward and
Lewellan, uses the key line signal from a
companion transmitter to switch off an
FET to reduce audio levels during transmission. However when the key line is
closed and the FET is turned off (its gate
will be negative with respect to its
source), some audio signal is still provided through R23 to produce a readymade sidetone for the operator.
Audio Amp
The SOP uses the ubiquitous LM386 in
the audio output stage. This device has
sufficient drive for headphones; a loudspeaker can also be used in a quiet room
when receiving strong signals.
SOP Receiver Assembly Manual, rev B
R13 and R25 keep the FreqMite audio
annunciator from being affected by the
setting of the AUDIO LEVEL potentiometer.
R26 and C29 serve to decouple the amplifier from the power bus. This prevents
the strong output signals of the LM386
from getting back to other components
in the receive chain.
C30 sets the amplifier to the maximum
available gain. C31 provides low impedance DC decoupling. R27 and C32 provide feedback to lessen high frequency
hiss in the audio output. R28 and C33
dampen the output of the amplifier to
minimize high frequency oscillation and
Here are the steps to follow in putting
your SOP Receiver Kit together. Refer
to the Parts List on the next page for a
description of each part in the kit.
1. Parts Inventory
Check out the contents of your kit to ensure that all parts are present. As you
identify each component, put a little
checkmark next to that line item, or write
the number of components you count up
for the lines containing multiple parts of
the same value.
The most of integrated circuits (ICs) and
transistors will be found pushed into an
anti-static foam pad.
The mixer integrated circuit (U3) is a
“surface mount device”, or SMD. It is
contained in a little 1/4” x 1/4” square
plastic container with a clear plastic cover.
We’ll describe how to mount this when
the time comes, but don’t worry about it
right now ... it’s a piece of cake!
2. Other Things Needed
You’ll need some common tools and
things normally found on the workbench.
Soldering tools: A fine-tipped, low-wattage soldering iron will be important to
have available. Ideally, a temperaturecontrolled solder station has been found
to be of great service to many
homebrewers and kit builders. I’ve found
that setting the tip temperature to about
650-degrees works best. Use of a wet pad
or rag for wiping the tip just before soldering a component lead keeps the tip
clean and free of oxidation and carbon
crud. A supply of standard 60/40 solder
from Radio Shack (p/n 64-009) will work
just fine. And finally, to clean up the inevitable solder shorts, many builders have
had great success using SolderWick, a
braided wire to help soak up the solder
bridges when heated.
The basic tools needed in putting together a kit such as this include fine-point
needle nose pliers, wire (side) cutters, a
small-blade screwdriver for adjusting the
IF transformer cans, and an Exacto blade
for general probing around and scraping
off the insulation from the magnet wires
when making the transformers. Other,
more elaborate tools can be useful but are
not required. These might include tweezers for holding very small parts, “third
hand” device for holding the board at
various angles, and a lighted magnifying
glass .
Connecting wire: About 5” of thin gauge
hook up wire will be needed for the single
jumper on the board. And you’ll need
some additional wire to connect your favorite controls and jacks to the board. Individual wires, strips of ribbon cable, and
thin RG-174 coax are examples of such
hookup wire that you probably have this
laying around your workbench or in the
junk drawer.
Off-board components: In order to complete the SOP Receiver kit, you’ll need
to supply the two potentiometers for the
“front panel” controls (Tune and Audio
Level) and the four “rear panel” jacks
SOP Receiver Assembly Manual, rev B
De signator
C4, 5
C22, 24
22pF Disc
47pF NPO
100pF Disc
220pF Disc
680pF NPO
capacitor, orange, "22"
capacitor, orange, "47"
capacitor, orange, "101"
capacitor, orange, "221"
capacitor, orange, "681"
C23, 25
C8, 15, 27, 32
15, 16, 18, 20, 28, 33, 36
C19, 21
C30, 34
C29, 37
0.1uF Mylar
.01uF Mono
2.2uF Elec.
10uF Elec.
47uF Elec.
100uF Elec.
capacitor, larger, dark red, "104"
capacitor, trimmer, w hite, 3-pins
capacitor, blue, "103"
capacitor, orange, axial lead, "M074"
capacitor, blue, radial lead
capacitor, blue, radial lead
capacitor, blue, radial lead
capacitor, blue, radial lead
R26, 28
R4, 30
R3, 19
R1, 2, 6, 11, 13, 15, 16, 27
R22, 23
L1, T2
455KHz IF
red "donut" core
5-lead "can", 42IF124 (Mouser)
8-pin, integrated circuit, DIP
8-pin surface mount IC, tan
8-pin, integrated circuit, DIP
8-pin, integrated circuit, DIP
Q1, 2
Q3, 5
3-pin transistor, 2N2222A, TO92 case
3-pin transistor, 2N5485, TO92 case
3-pin transistor, 2N3565, TO92 case
2-pin varactor TO92 case, "V149"
glass diode, band = cathode end
3" x 4"
toroid w ire
pc board
3-pin 6V regulator, TO92 case
ceramic resonator, 2-lead, "3.58G"
red, enamel-coated magnet w ire
green, ground plane bottom side
Magnet Wire
PC Board
De scr iption
resistor, yellow -violet-black
resistor, brow n-black-black
resistor, yellow -violet-black
resistor, brow n-black-brow n
resistor, red-red-brow n
resistor, brow n-black-red
resistor, red-red-red
resistor, yellow -violet-red
resistor, brow n-black-orange
resistor, red-red-yellow
resistor, brow n-black-green
SOP Receiver Assembly Manual, rev B
(Ant, Keyline, Phones, +V). It’s up to the
builder as to what kind of jacks are used,
but the controls must be the correct value
(10K-ohm) shown in the schematic. There
is an optional controls and hardware
“add-on kit” available from the NJQRP
Club that conveniently provides these
components at a nominal price. Section
4 of this manual overviews assembly of
this add-on kit.
IC Sockets: The only other “nicety” that
would be reassuring to novice builders
would be to use sockets for integrated
circuits U1, U4 and U5. Each of these ICs
is an 8-pin DIP package, and use of a
good-quality, low-profile, machined-pin
socket would allow you to remove/replace
the IC during troubleshooting and while
making modifications further downstream. These IC sockets can be found at
Radio Shack.
Test & measurement equipment: The
basics needed here include a VOM (voltohmmeter) to measure DC voltage levels, check resistor component values, continuity, etc. An RF probe adaptor for your
VOM is very useful in measuring RF
voltages and AC signals at various points
in the circuit. We’ve included plans in
Appendix A for a simple RF probe if you
don’t already have one. Similarly, many
builders find it quite helpful to be able to
inject audio tones into their projects at
various points to help determine if the circuits are working. We provide plans in
Appendix B for a simple audio oscillator. Other more specialized (and expensive) pieces of equipment may also be effectively used. The first, and most versatile, is an oscilloscope (20 MHz or higher
is preferable). Many guys find that an inductance-capacitance meter is invaluable
in assuring correct component selection
and toroid inductances ... the LC Meter II from AADE is just fabulous and relatively inexpensive. Another extremely
useful piece of equipment to have when
working with RF circuits is an antenna
analyzer, like the RF-1 Analyst or the
MFJ-259 series. These serve well at injecting RF signals to receiver front ends,
detecting RF output, and (with simple
adaptors) measuring the values of inductors and capacitors.
If you don’t have the basic items readily
at hand, now would be a good time to
make a quick trip over to your local Radio Shack to stock up on these wires,
tools, solder and other standard items
used in electronic kit assembly.
3. Start with the PC Board
Okay, let’s get acquainted with the printed
circuit board, or “pcb”. If you orient the
pcb with the green side up, you’ll see that
it contains a majority of the traces and
component designators for this project.
All components will be inserted from this
top side of the board shown with the designators and traces on it.
You might need to hold it at just the right
angle for the light to clearly show the
component designators (e.g., R1, C21,
etc.), and you might even need a magnifying glass to see it clearly. Again, not to
worry because the PCB Layout figure on
page ___ should be big enough for anyone to see things! This diagram will be
your roadmap for placing the components
onto the board.
(The next revision of the board will have
a “silk screen” of component outlines and
designators. Although this makes the
board a bit more expensive to manufacture, it makes it even easier to populate
the board.)
Place the pcb so you can read “FB Rx REV
B N2APB (COMP. SIDE) ” along the top
edge. All input and output wires and
cables will be soldered to the board at
pads along the four edges of the board.
Starting at the top left corner and proceeding counter-clockwise, you’ll see pads labeled: ANT, TUNE, SPOT, PHONES,
SOP Receiver Assembly Manual, rev B
AUDIO, KEY, and +V. Most of these in-
put/output pads have ground pads (labeled GND) close by to provide you with
a convenient way to use shielded wire or
twisted pair wire and have the ground line
of the wire connected to the board ground
plane right at the signal pad.
Mounting holes are provided in each corner of the board to allow use of standoffs
to hold the board in your favorite enclosure. These holes are connected to the
board ground plane, so if you are a purist, you might want to be careful to isolate the board from a metal enclosure (if
used) so as to help eliminate the possibility of ground loops in your receiver ”system”. If you purchased the SOP Enclosure option, nylon spacers are provided
for this purpose, thus isolating the board
ground plane from the chassis ground.
Turning the board over you will notice a
pervasive amount of tinned copper serving as the ground plane. This ground
plane encircles most component pads,
providing a good shield for the low-level
signals in the circuit. You’ll be soldering
almost all of the component leads to the
respective pads on this bottom side of the
pcb, so you’ll need to be careful not to
accidentally bridge solder from the component pad being soldered over ontop the
encircling ground plane. You should carefully inspect each soldered connection to
check for these solder shorts and correct
them right away.
4. Installing the Components
You are now ready to install and solder
the parts onto the printed circuit card. Be
sure to ear mark (or paper clip) the pages
containing the Parts List and the PCB
Layout, as you’ll often be referencing
them. You’ll also notice that outlines of
the component packages is indicated on
the PCB Layout diagram. This will
greatly assist in properly positioning the
components onto the board before soldering. For example, polarity of the electro-
lytic capacitors is indicated on the PCB
Layout diagram, shown with a “+” symbol near one of the two capacitor pads.
Be sure to check the full-page SOP Schematic in the center of this manual to help
answer any questions you might have
about proper positioning of components
during assembly or connection of the offboard controls and jacks.
We’re going to assemble the SOP Receiver in stages, and test each stage as we
go along. This will give you the best shot
at having an operational receiver when
assembly is complete.
With our cumulative years and years of
kitbuilding experience in the NJQRP
Club, we offer some advice to make
your kit construction a most pleasurable experience. Take your time during
assembly. Read through all the description in each section before starting to solder anything. As you accomplish each
step within a section, put a little
checkmark in the little box provided at
the start of each operation in order to help
you keep track of what’s been done and
what’s remaining. Take a short break and
give yourself a reward (coffee, chocolate,
a quick QSO on 40m, etc) in between
each section built up. And when you’re
all done and the receiver is working as
expected, do the Happy Dance throughout the home and neighborhood to let
everyone know of your wondrous accomplishment!
We’ll start the ball rolling by building up
the Local Oscillator. This is a sensible
place to start in that this portion of the
circuit requires no other signals for it to
work. You build it and it works! ... Well,
we hope it works; and if it doesn’t, we’ll
hop in to find the problem right away.
Let’s begin!
Install mixer IC “U1” -- If you are
using IC sockets (recommended) orient
SOP Receiver Assembly Manual, rev B
the socket in the holes for U1 such that
the pin 1 corner of the socket is in the
hole with the small square pad. If a socket
is not being used, place the IC in these
holes directly, ensuring that pin 1 goes
into the square pad. (Pin1 is located just
to the left of the detent-marking on the
top side of IC package.) You might need
to gently push the rows of pins closer together for them to fit into the rows of
holes in the board. Holding the socket (or
IC) in place, turn the board over and gently bend several of the pins outward so
the part stays in place. Then, with a
warmed and tinned soldering iron, solder each of the 8 pins in place. Inspect
the pads when done to ensure that no solder bridges exist to ground. (Note that pin
3 will be connected to ground by small
descriptions in the Parts List, locate the
specified capacitors and install them at
the designated positions. As you put each
in place, slightly bend each component
lead outward so as to hold it in place while
you put the others in. When all of these
caps are in, turn the board over and carefully solder each to its pad. Using side
cutters, snip off the excess lead length
close to the solder joint. Check for solder
bridges and correct if necessary.
Install resistor “R10”-- Locate
R10 and ensure that it is the right value.
Carefully inspect the color coding on the
resistor body to ensure you have the right
one. A bright light and a magnifying glass
might be helpful. Sometimes resistors lie
flat against the board, but in this kit the
resistors will be mounted in an upright
position, as shown below.
Install IF Transformer “L1”-- Locate one of the IF transformer cans and
align it in position just above and to the
right of U1. Insert it into the holes - three
on one side and two on the other, with
the tabs of the can extending down into
the larger holes. IMPORTANT: Make
sure the can is sitting just a hair (approx
1/16’) above the board so the metal can
will not contact the trace running underneath the part. When soldered, this can
will be “ground” and would short out the
oscillator. Carefully turn the board over
and solder the 5 transformer can leads, as
well as the larger tabs. Check for solder
bridges and correct if necessary.
Install Crystal Resonator “Y1”-Locate the little dark orange resonator,
marked as 3.58MG, and insert at the location for Y1, just to the left of U1. Holding it in place, turn the board over and
carefully solder its leads. Using side cutters, snip off the excess lead length close
to the solder joint. Check for solder
bridges and correct if necessary.
Install Capacitors C13, C16, C2,
C3, C4, C5, C6 and C7 -- Using the
Once again, solder and snip the excess
lead length. Check for solder bridges and
correct if necessary.
Install Varactor Diode “D1” -Locate the 2-wire varactor component
and notice the flat side of the package.
Orient the package as shown in the PCB
Layout diagram, and insert into its pad
holes with the flat side toward the top of
the board. Carefully spread the leads on
the bottom side of the board to hold it in
place, then solder the pads and snip the
excess lead lengths. Check for solder
bridges and correct if necessary.
Install Voltage Regulator “VR1”
-- Locate the VR1 component and orient
it as shown in the Layout diagram, with
its flat side toward the bottom, and insert
it in the three pad holes. Carefully spread
the leads on the bottom side of the board
to hold it in place, then solder the pads
and snip the excess lead lengths. Check
SOP Receiver Assembly Manual, rev B
for solder bridges and correct if necessary.
Install R7 and R8 “jumpers” -Using short pieces of component leads
(snipped off in prior steps), bend each
over into tight “U” shapes and insert into
the positions for R7 and R8 on the board.
Spread the leads on the bottom of the
board and solder in place. Snip off excess lead length and check for solder
bridges. These “zero-ohm resistors” can
be later changed to real value resistors and
used to pad the tuning control R9. This
will be described later in greater detail.
Install tuning potentiometer “R9”
Obtain the potentiometer you wish to use
for the TUNE control (from your junk
box, Radio Shack, or from the optional
SOP Controls Kit). Using short lengths
of hookup wire, connect the pot as shown
in the PCB Layout diagram. You’ll probably later use longer, shielded wire to
connect this pot when installed in an enclosure.
q Check for RF OSCILLATION -Using the RF Probe (from Section 5, or
equivalent) attached to your VOM, measure the RF voltage on U1 pin 7. You
should see some millivolt reading to
indicates that the circuit is oscillating.
If you do not see a reading on the VOM,
carefully check all components for
proper orientation, and for solder
shorts. An oscilloscope would indicate
that the circuit is oscillating at approximately 3.58 MHz without jumper C in
Insert a jumper between pads C-C just
to the left of U1 (in a manner similar as
the zero-ohm resistors R7 and R8), and
measure the oscillator output on U1 pin
4. If you were using an oscilloscope,
you would detect oscillation occurring
at approximately 7.1 MHz, because of
the “doubling” effect of U1. A small
reading should also be seen on this pin
with the RF Probe and VOM. The signal would “peak” at some point as you
adjust the slug inside the IF can L1, indicating that the L1-C7 tank circuit is
properly adjusted for 40m operation.
Testing the Local Oscillator
It’s time to test what you’ve done thus
far. Carefully inspect all your work to
make sure you didn’t miss anything,
that traces are not shorted, and that
everything is soldered properly.
Connect up a 9V battery (or equivalent)
to the +V and GND pads along the right
side of the board. We’re using a battery here to reduce problems in case
of inadvertent shorts on the board ...
the battery is self-current-limiting and
doesn’t supply tons of current like a
regulated power supply when there are
q Check for +6V -- The first thing to
do is to check to see that VR1 is working. Using your VOM, ensure that there
is +6V on U1 pin 8. If you don’t see this,
stop right away and determine the
cause. Is VR1 getting hot? (If so a
shorted output line might be present.)
Is the +V supply voltage making it to
the VR1 input pin?
We’ll next assemble and test the two-transistor buffer amplifier for the LO.
Install transistors “Q1” and “Q2”
Locate the two 2N2222A transistors and
put them each into their 3-hole positions
on the board with their flat sides facing
toward the right. Slightly spread the component leads on the bottom side to hole
them in place, and carefully solder the
leads. Trim the excess lead length and
inspect the pads for solder bridges.
Install resistors R2, R3, R4 and
R30 -- Locate these resistors by carefully
studying the color bands, per the Parts
List line descriptions. Install them in the
“upright” manner previously described
for R10. Gently spread the leads on the
bottom of the board and solder them to
the pads. Clip off excess lead length and
inspect for solder bridges.
SOP Receiver Assembly Manual, rev B
Install capacitors C8, C9 and C12
These caps are all the same. Install them
through their respective pads on the pcb,
spread their leads slighty on the bottom
side of the board, and solder each one
carefully. Snip off excess lead length and
inspect for solder bridges.
T1 is a “bifilar-wound” inductor on a toroid core, meaning that you’ll be combining two magnet wires together and winding them at the same time. Measure off
two 7-inch pieces of red magnet wire.
These wires should be twisted together
as illustrated below.
Install capacitor C10 -- This capacitor actually does not have a pair of
holes on the board (a slight oversight on
this version of the pcb), so you’ll install
in on the bottom side of the board. Carefully locate the pad for R30 and its corresponding trace going over to T1. You’ll
solder one side of the 0.1uF C10 to this
trace, and the other side of the cap to
ground. See the diagram below for reference.
Winding and installing T1 -- This
is a fun part of the project that some
homebrewers worry about. There’s actually nothing very hard in winding a few
turns of wire through the toroid core, and
we’ll take you through it in a step-by-step
(Just twist the wires loosely together by
hand ... they don’t have to be very tightly
wound at all.)
You will then wind the combined, twisted
wire pair around a black FT37-43 toroid
core. See the diagram below for proper
connection of the four leads:
a b
Install C37 electrolytic cap -- This
capacitor also has something screwy
about it ... it goes into the holes marked
C14. But curiously, there are two C14
positions marked on the board (another
minor error in the pcb) ... our 47uF C14
electrolytic goes into the position marked
with a round symbol in the Parts Layout
diagram. Make sure the positive side of
the cap goes into the hole marked with a
+ symbol. (The positive lead is the longer
one on the side opposite the lead marked
with the “-” symbol on the side of the
You’ll next need to strip off the red
enamel coating from the transformer
leads. The heat strippable magnetic wire
being used requires no scraping to clear
the red insulation off the leads being soldered to the PCB pads. Once the wires of
each inductor are trimmed to the right
length (approximately 3/8” extending
down past the bottom of the core), tin the
ends of the wires by doing the following.
Using a good hot soldering iron, place
the tip under the end of the wire to be
tinned and add a little solder so that there
is a small pool of molten solder and flux
on top of the iron with the wire in the
SOP Receiver Assembly Manual, rev B
pool. After several seconds, the insulation will melt away and the wire will be
tinned where it is in contact with the iron.
Continue moving the iron slowly toward
the toroid core adding solder as you go,
until the wire is tinned within 1/16 inch
or so of the core. Repeat the procedure
for the other 3 leads and brush off any
carbon residue from the ends of the wires.
You’ll next connect two of the leads together to form the center tap of the transformer. When two wires of the same color
are twisted and wound together on a toroid, it’s difficult to know which ends to
connect together to form the center tap.
You will need to use an ohmmeter to determine proper ends. As indicated in the
diagram on the previous page, one of the
wires, a is the start and a’ is the end. On
the other wire, b is the start and b’ is the
end. You should twist wires a’ and b
together to form the center tap.
Insert T1 into position on the circuit board
as shown below. The centertap is in between the two end leads.
This is just to the right of IF can L1. This
jumper will select the 40m signal from
the LO.
Testing the LO Buffer
Now it’s time to test the LO Buffer you
just installed. Apply power again and
using your RF Probe and VOM, measure some signal on the emitter of Q1
(the lowest of the 3 transistor pads).
Next measure some significantly
greater voltage on the top end of capacitor C12 at the Buffer output.
If you do not see signal readings at
these locations, go back and check for
solder bridges and proper component
placement. Your receiver will not operate without sufficient “LO injection” to
the mixer stage.
We’ll next assemble and test the RF front
Install trimmer cap C20 -- Locate
this trimmer cap ... it’s a larger, 3-terminal component with a slotted adjustment
on the top. Orient it in the 3 holes of the
pcb such that its third “extended” tab is
in the bottom-left pad. See below.
Trim the leads to the correct length, prepare the ends with the soldering iron
again, and solder them into their respective pads on the pcb.
We’ve found that over 90% of most kit
assembly problems come about because
of improper tinning and soldering of toroid inductor leads, so please be sure that
you carefully followed the instructions in
this section.
q Install jumper J2 -- Solder a short
length of a discarded component lead in
place between pads 1 and 2 at jumper B.
Install IF can T2 -- In a manner
similar to what was done for the L1 IF
can, install another at position T2. Again,
be sure not to have T1 sitting flat on the
pcb ... you must solder it in place such
that it sits about 1/6” above the board
Install FET Q3 -- You’ll need to
carefully swap the right two legs of this
transistor when inserting it to the pads on
the board. (There is a routing error on the
board.) Reference the following diagram.
SOP Receiver Assembly Manual, rev B
Testing the RF PRE-AMP
Install C15 and R11 -- Locate these
two components and install them in position below trimmer cap C20.
Construct and install T1 -- Okay,
it’s time to make yourself another transformer! This one is also pretty easy to
do. Measure off about 20” of red magnet
wire and wind 36 turns around the red
toroid core. But at the second turn extend a little extra past the core body and
twist it together to form a tap. Continue
winding the rest of the 36 turns. This will
be the secondary winding of the transformer. Measure off another length of red
magnet wire, this time only about 3” and
put 2 turns around the core overlapping
the lower two windings of the primary,
right up to the tap you created.
Connect a temporary wire from the output of the LO Buffer (top side of C12)
to the ANT pad at the input of the RF
front end. This jumper will supply a
known-good frequency that we can use
to test the front end.
Apply power to the board and using the
RF Probe measure the signal on the T1
secondary winding, located at the left
side of R11. While watching the VOM
reading, adjust the trimmer cap for
maximum readings.
Move the RF Probe over to the secondary of T3 (can be probed on pad 3 of
U3). Again while watching the VOM
readings, peak the IF can T2 using a
small screwdriver.
If you did not see noticeable signals at
these points, or if the circuits did not
peak as described, go back and check
for proper components and solder
bridges. Be especially careful in
double-checking the construction job
on T1.
Remove the temporary jumper from the
LO Buffer.
We’ll next put the mixer chip U3 in position.
p p’
Tin the leads as done before and insert
onto the board at position T1. The two
(short winding) primary ends will go into
the two pads on the left, and the three secondary leads (two ends and the centertap
in the middle) will go into the pads on
the right side of the component. Solder
all 5 leads in place, ensuring that no enameled wire is in the solder junctions.
Install mixer U3 -- This integrated
circuit is a “surface mount chip”, but it’s
a rather large one and relatively simple
to put in place. We were going to provide this part pre-soldered on the board
but found it to be so straightforward that
we felt most kit builders could easily accomplish it.
First tin pad 6 of U3 on the board. This is
the top right pad in the array of 6 pads
for U3. By tinning this pad, you are depositing a small ball of solder to the pad
that will be re-heated with the IC in place,
thus holding it down while you solder the
SOP Receiver Assembly Manual, rev B
other pins.
Next, locate the IC in the black plastic
case with the clear top. Carefully peel
back the top cellophane membrane and
the IC will fall out onto the table.
Pick up the IC with your fingers or with
your needle nose pliers and place over the
pads on the board with pin 1 in the top
left corner. (Pin 1 is denoted by a small
dot in the tan plastic package.)
Making sure that the pins of the IC are
properly positioned over their respective
pads, carefully touch pad 6 with the tip
of the soldering iron and “reflow” the
solder while gently pushing the IC down
onto the pad. With only a small amount
of luck, the IC will be held firmly in place
by that one pin, with the other 5 pins
clearly oriented over their pads. (If not,
reheat pad 6 and adjust the IC to be correctly positioned.)
Go to the each remaining pin and solder
it to the pad beneath it. The pins have
about the standard 0.1” lead separation,
so this operation should be a piece of
cake. Carefully inspect the pads for shorts.
There’s nothing to easily test at this point,
so we’ll go on to add the audio filter and
amplifier stages next.
this as a signal injection point during test
in a few moments.)
q Install transistor Q4 -- Note this
package orientation on the Parts Layout
You’ll next assemble the Low Pass Filter stage.
Install resistors R15, R16, R17,
R18, R20, R21 -- Nothing tricky here.
Install capacitors C22, C23, C24,
C25 -- Nothing tricky here either except
to ensure that you grab the correct caps
for C23 and C25. These are the dark
brown mylar .01uF caps.
Install integrated circuit U4 -- This
is pretty straightforward, as long as you
ensure you get pin 1 in the square pad.
Again, you might want to use a socket to
help with later debug or modifications.
You’ll next assemble the Muting stag:
Install resistors R22, R23 -- Nothing tricky here.
Install capacitors C27, C28 -Nothing tricky here either.
You’ll next assemble the Audio gain
stage: Q4. (You’ll actually assemble all
four stages of the audio chain before we
test them.)
Install resistors R14, R31, R19 -Note that R31 is installed at position R29
along the top of the board. (A small typo
on the board designator.)
q Install capacitors C19, C36, C21,
C34 -- Be careful to observe polarity of
the electrolytic capacitors. The positive
pad is indicated with a ‘+’ on the board.
Leave the left end of C19 up in the air,
unconnected to the left pad. (We’ll use
Install diode D2 -- Just be sure to
orient this glass-packaged part with its
cathode (banded end) into the lower of
the two pads.
Install FET Q5 -- Here again you’ll
need to carefully swap a couple of the
legs (this time the left two) of this transistor when inserting it to the pads on the
board. (There is a routing error on the
board.) Reference the following diagram:
SOP Receiver Assembly Manual, rev B
coaxial dc power jack to the +V and GND
Connect R9 to TUNE-- Using your
selected hookup wire or cables, wire the
remaining pot to the tuning pads TUNE.
q Install pot R24 -- Here’s the first
instance that you’ll have to install an offboard component. Make sure that you
select the right pot (i.e., the one with the
extra two tabs on it) and wire it as shown
in the Parts Layout diagram.
You’ll now install the final stage of the
receiver: the Audio Amp.
The figure on the next page represents a higher-level view of the
SOP audio section. Debugging process starts at its output then proceeds backward toward the input.
Going at it this way lets you hear
what’s going. In the interest of
brevity (and saving trees) we’ll
show the debug steps and results
in summary form.
Install resistors R13, R25, R26,
R27, R28 -- Nothing tricky here.
Install capacitors C29, C30, C31,
C32, C33 -- Nothing tricky here either
except to ensure that you are careful to
install the electrolytics with the proper
Install integrated circuit U5 -- This
is pretty straightforward, as long as you
ensure you get pin 1 in the square pad.
Again, you might want to use a socket to
help with later debug or modifications.
For the final installation of parts, you’ll
need to connect up the remaining offboard controls and jacks. This will enable you to fully test, and then later operate the receiver. Refer to the Parts Layout diagram in the center of this manual
for graphic detail.
Connect J3 to PHONES-- Using
your selected hookup wire or cables, wire
the 3.5mm audio output jack to the
PHONES pads.
Connect J1 to KEY-- Using your
selected hookup wire or cables, wire the
RCA phono jack to the keyline input at
pads KEY.
Connect J4 to +V-- Using your selected hookup wire or cables, wire the
Connect J2 to ANT-- Using your
selected hookup wire or cables, wire the
RCA phono jack to the antenna input at
pads ANT.
Testing and Troubleshooting the
Audio Chain
1) Connect power - no smoke! Use
a 9 volt alkaline battery to minimize
damage if something was not right
in the circuit.
2) Check pin 6 of U5- should be
about 1/2 supply voltage.
3) Using an audio signal source
(like the one in Section 5), apply audio to top of volume control. A
tone should be audible in the
speaker or headphones.
4) Apply audio to input of the mute
switch. You should hear a weak
5) Check the dc bias on the output
of low pass filter (U4 pin 7). Should
be 1/2 supply voltage.
6) Check bias divider on the low
pass filter input. Should be 1/2
supply voltage.
7) Apply the audio source to the
input of the low pass filter (junc-
SOP Receiver Assembly Manual, rev B
tion of R15 and R16). Should hear
tone in loudspeaker and volume
control should work normally.
8) Ground the KEY input pad with
a clip lead. The tone should disappear.
9) Connect the audio signal source
to the input of the entire audio
chain (i.e., at the lifted end of C19
in the Audio Gain stage). You
should hear a very loud signal, and
it can still be adjusted using the
R24 level control.
The only assembly operation needed at
this point is connection of the Mixer stage
output to the Audio Gain stage input.
Connect left side of C19 to its pad
When you connect a proper antenna to
the ANT input pads (or the J1 jack), you
should hear a significant amount of activity as you tune through the SOP’s frequency range (depending on the time of
day and band conditions).
Now would be a good time to find a
known-frequency signal on the band, or
use another, calibrated receiver in order
to determine the specific frequency coverage of your SOP Receiver. Finding the
band edges and marking your front panel
accordingly would be real useful when it
comes time to operate the receiver.
Of course, if you have purchased and installed the AFA option, you’ll hear the
exact frequency of operation come
pounding out at you in Morse code from
the on-board frequency counting circuit
of the PIC.
Putting the SOP receiver on 80m is relatively easy. You’ll need to add a few components, and change a couple of jumper
settings on the board, but there’s nothing
SOP Receiver Assembly Manual, rev B
major. Just follow the notations on the
schematic. These minor mods are primarily in the Local Oscillator stage and the
RF Pre-Amp stage.
That is, if you have problems in getting
your SOP to operate, feel free to contact
us by email or US Mail and we’ll do what
we can to help.
You’ll notice that the TUNE pot is connected to the regulated 6 volt regulator.
This was done to provide a nice, clean,
stable signal for the voltage presented to
the varicap tuning element. Without such
regulation, the set frequency would drift
when the power source (e.g., battery)
drooped, dipped, glitched, sagged or otherwise varied due to being weak.
For a nominal, flat fee, we will provide a
repair service that will guarantee you getting back a working SOP (as long as there
was no major component or pcb damage).
Contact us for details on this last resort
If one were to instead provide the higher
+V unregulated voltage to the top of the
TUNE pot (and its padding resistors),
while at the same time provide a stable
+V source, a wider swing in frequencies
would be achievable.
Like we said up front, the SOP Receiver
is an ideal experimenter’s platform!
There are many mods coming down the
pike for this project.
- taking the SOP to other HF bands
- improving the gain and sensitivity
Thanks a whole bunch for buying the
SOP Receiver Kit and experiencing the
fun of homebrewing your own rig with
us. The NJQRP Club put in a tremendous
number of hours designing and putting
this kitting project together for QRPers
all over the world, and we sure hope you
are pleased with the experience.
As we stated up front, the SOP is an
experimenter’s platform for learning
about basic receiver operation, straightforward homebrew kit building, and
when all complete it’s a flexible little receiver for portable use. And if you’ve
come this far in the manual, you surely
have gained a whole lot of this good experience along the way!
- using alternate designs for some stages
- provide multi-band operation with
“daughter boards”
- providing a wider range in the LO
--George Heron, N2APB
[email protected]
- etc.
There will be some “application notes”
published and distributed to the SOP
owners, allowing you to have some
greater visibility into the fun times ahead.
Lots of plans!
-- Joe Everhart, N2CX
[email protected]
And be sure to visit the SOP Receiver
web page at the NJQRP Club website:
SOP Receiver Assembly Manual, rev B
Section 2:
Audio Frequency
Annunciator (“AFA”)
Assembly Manual
We were able to design in a great feature, in cooperation with Dave
Benson, NN1G, to provide the Small Wonder Labs “Freq-Mite” audio
frequency annunciator PIC chip and associated components as an
optionally-purchased add-on to the SOP Receiver. This option provides an incredibly useful feature of an “audio frequency dial” that delivers the operating frequency of the receiver in Morse code through
the audio chain of the receiver. With this option installed on the base
PC board, the operator merely presses a front panel “spot” button to
hear the operating frequency delivered in Morse code through the headphones or speaker. It’s always accurate and there’s no front panel
space necessary to know where you are in the band. NN1G was very
pleased to be able to contribute his Freq-Mite functionality at a very
attractive price to those purchasing SOP kits.
Circuit Description
This circuit from Small Wonder Labs is
really quite simple, yet clever. Referring
to the schematic in Figure 2, a PIC16C621
microcontroller is programmed as a frequency counter.
ing the SPOT pushbutton, an output bit
is wiggled at approximately 600 Hertz,
and then modulated on-and-off to send
the Morse code equivalent of the measured frequency through capacitor C43
and on into the audio amplifier.
Transistor Q6 buffers, amplifies and conditions the signal coming from the Local
Oscillator and presents it to an input port
of the PIC. The PIC then counts the number of low-to-high transitions of the signal during a specified period of time, and
voila, the frequency is known.
Resistor R43 is used to reduce the amplitude somewhat so the Morse frequency
doesn’t wake the next door neighbors.
(This is a high-value resistor, and you
may need to adjust it up or down to suite
your particular needs. Just substitute a
higher or lower valued resistor if desired.)
But wait, that’s only half the beauty of
this circuit. The other purpose of the PIC
is to output the computed frequency in
Morse code!
Because this high-speed digital circuit is
sitting pretty close to low-level RF circuitry, we took some special precautions
to reduce electrical noise and cross-coupling.
When commanded by the operator press-
SOP Receiver Assembly Manual, rev B
R 40
C 42
. 01
R 42
R 41
Loc al
C 44
. 0022
Value t o suite desired
out put lev el: 2.7M-t o-3.9M
R A4
R A1
R 43
I nput
R An, 1,2,17, 13,12, 11,7
16C 621 R Bn
Vs s
Pushbutt on
C 43
6 R B0/ IN T
Osc 1
Osc 2
4.096 MHz
C 41
C 40
The circuit is operated at the lower end
of its voltage range, as determined by the
4.3 volt zener diode. This lower operating voltage produces significantly less
energy in its digital waveforms and thus
minimizes interferences to the receiver.
fining the perimeter of the microcontroller
circuit, allowing for a small pcb-cage to
be soldered in place to further isolate digital RF coupling. But we found that this
precaution was unnecessary and it was
not included in rev B of the pcb.
The PIC circuitry is tucked into a corner
of the pcb where its effect would be least
noticeable and where cross-coupling
would be minimized.
For those who have previously used the
Small Wonder Labs’ FreqMite, you’ll
know that an “offset” can be set into the
PIC’s computation, thus yielding an adder
to the base frequency being measured.
This allows the FreqMite to be used to
measure signals in multi-mixing stage
superhet designs where the VFO frequency is not the actual “displayed” frequency. But here in the direct-conversion
SOP, the Local Oscillator signal is the
operating frequency and the PIC is configured through pins 1, 2, 17, 13, 12 11
And finally, the ground plane for this circuit on the bottom of the board is isolated, except for one joining point, thus
preventing digital return paths from flowing past or through the RF or audio circuits.
In earlier prototypes of the SOP, we had
wide ground traces on top the board de-
SOP Receiver Assembly Manual, rev B
De signator
4.3V zener diode
4.096 MHz crystal
brow n, 103
brow n, 104
glass, band at cathode
3-pin TO92 case
yellow -violet-brow n
brow n-black-yellow
orange-w hite-green
18-pin DIP IC
2-w ire metal case
and 7 to provide a Morse readout of the
actual frequency being measured. Thus,
when the LO is tuned to 7.040 MHz, the
AFA will output “7040” to the phones/
speaker in Morse code when the SPOT
pushbutton is depressed.
place in the pcb at Y2. Do not have it sitting flat on the pcb surface ... you should
solder it in place such that it is raised about
1/6” above the board, ensuring that its
metal case is not touching the traces beneath it.
Once again, the first thing to do is to check
the contents of the separate bag containing the AFA parts. (This bag has a label
in it indicating that it’s the AFA parts
bag.) This accessory only contains the
parts required for the AFA feature, and
the components will be placed on the
main SOP pcb.
Install PIC uC U6 -- Locate the
integrated circuit in the black antistatic
pad and insert it in the holes for U6 on
the pcb. Be very careful to ensure that
pin 1 of the IC (at the left side of the end
with a detent in the plastic body) goes into
the square pad. (The rest of the pads of
the IC are round.) It would be a good thing
to solder in an 18-pin socket first, instead
of soldering the IC directly in place. This
would allow you to remove/replace/re-use
the PIC in other design should you need
to later on.
Install crystal Y2 -- Locate the lowprofile 4.096 MHz crystal and put it in
Install zener diode D3 -- Locate
this glass diode and insert it in an upright
position (like you do for the resistors) at
position D3. Be sure to orient the diode
such that the cathode (i.e., the banded end)
is the end connecting to R4. It would be
best to have this cathode end be the one
sticking up with its lead folded over. This
way you’ll more easily be able to probe
the circuit later for proper voltages.
Install C43 and R43 -- You’ll be
putting these two components into “the
same” location on the pcb. The left leg of
C43 will be inserted in position just below Q6, and its other leg will be pointing
straight up. Thus the component will be
leaning to the left. R43 should be inserted
to the right hole of C43 on the pcb, and
the other end which is also sticking
straight up should be soldered to the uppointed leg of C43. Thus, these two components will be in series. See the figure
on the next page for reference.
SOP Receiver Assembly Manual, rev B
Install remaining components:
C40, C41, C42, C44, R40, R41, R42,
and Q6.
Clip leads & inspects for solder
bridges -- As always, trim all leads down
after soldering and carefully inspect the
bottom side of the board for solder
Install Jumper A-A -- The last
thing you’ll need to do is to install a
jumper wire from pad ‘A’ at the middletop of the board (just above U3) to the
other pad ‘A’ just above pin 1 on U6. For
neatness, you could install this jumper on
the bottom side of the board - it doesn’t
matter. This jumper brings the LO signal
down to the PIC.
Upon power-up, the PIC sends an ‘S ?’ if
you press the SPOT pushbutton switch
within about two seconds, the chip
switches to a higher speed (26 WPM)
readout rate. It acknowledges this entry
with an ‘R’. If you do nothing the chip
maintains its default 13 WPM readout
Many thanks are due to Dave Benson,
NN1G and Small Wonder Labs for allowing use of his FreqMite circuit, for
providing us the pre-programmed PIC
microcontrollers at an attractive discount,
and for advising us on implementation of
the design into the SOP Receiver. Dave
is an active contributor to NJQRP design
and project teams.
SOP Receiver Assembly Manual, rev B
Section 3:
SOP Enclosure Option
Assembly Manual
This optionally-purchase Enclosure Kit is the ideal homebrew case for
your SOP Receiver. Consisting of 8 precision-cut double-sided copper clad boards and assorted hardware, this kit can be assembled in less
than 30 minutes and can be finished to the builder’s liking or used with its au natural
copper look.
The SOP Enclosure is a homebrew one
- one that you will assemble from its most
basic pieces. Don’t worry though, you
won’t have to go through the hassles of
scribing, bending and cutting metal;
we’ve already done all that work for you!
This do-it-yourself case is a little different than most that you may be familiar
with. It is not made of aluminum or steel
or even plastic. It’s fabricated from copper-clad glass-epoxy printed circuit board
material. Being homebrew, it is a fitting
companion to the SOP Receiver kit and
adds to the enjoyment of your project. All
you need to do is carefully follow the directions in this manual and you will find
it easy to make a very attractive case. No
drilling, sawing or punching is necessary;
only a little soldering is needed, and perhaps some touchup with a file. In fact,
once you built it you may even be inspired
to make your own pc board case for the
next homebrew project you have lined up.
Cases made of pc board stock have lots
of advantages over other material. The
raw material is relatively common and
easy to machine. It is lightweight and, in
small cases, quite strong. The copper surface provides a good continuous electrical shield for electronic circuits inside
while presenting an outer skin that can
be left “natural” or painted in any color
SOP Receiver Assembly Manual, rev B
you want.
If you want a short treatise on this construction method check out Joe’s Quickie
No. 34 in the Information Exchange column in the April 2000 issue of the QRP
The SOP Enclosure Kit consists of eight
pieces of printed circuit stock which will
be soldered to form the top and bottom
of a cabinet. (Skip ahead to Figure 2 to
see a set of diagrams depicting all supplied parts.) The case top is an open “U”
which sits over another open “U” formed
by the case bottom. The bottom also has
internal side rails which lend strength to
the front and rear panels, and to which
the top is connected via sheet metal
Also provided with the kit are the mounting hardware, knobs and jacks needed for
the SOP Receiver. Clear acetate sheet
overlays are even supplied to be used as
attractive labels for the front and rear panels.
It’s a good idea first off to identify the kit
parts and make sure that they are all
present. The following list details them
and identifies the cabinet parts by letter.
Match them to Figure 2 on the next page
and check them off in the list as you identify the contents of the parts bags.
Parts list -- Bag 1
a Top cover panel
b, c Two top cover side pieces
d Bottom plate
e Front panel
f Rear panel
g, h Two side rails
front panel clear acetate label
rear panel clear acetate label
right angle alignment gauge
(approx. 1 inch square)
Parts list -- Bag 2
3/8” Nylon standoffs
10 #4 x 1/4” sheet metal screws
Self-adhesive rubber feet
General Guidelines
Before we start construction, let’s start
off with a couple of tips in case you are
assembling a pc board enclosure for the
first time.
You will need only a couple of small tools
and supplies that are probably already at
hand. They will be discussed in the text
but here is a sample list:
- Soldering iron
- Non-acid solder
- Scotchbrite or other soap-free nonabrasive pad
- Flat file
- Alcohol or other non-water-based solvent
- Clear adhesive to attach panel labels
- Mechanic’s square (optional)
- Rosin core flux (optional)
- Paint (optional but an excellent choice
for durability is Rustoleum)
- Clear spray (optional though Krylon
clear protects copper from corrosion)
This process has a lot in common with
assembly using surface mount components. While ordinarily solder joints
should not be relied on for mechanical
strength, good joints are the only source
of strength for surface mounting and for
pc-board cases. So every effort must be
made to produce good joints.
High quality solder connections begin
with clean surfaces. While the copperclad board pieces in this kit are shipped
in good condition, the copper will form
an oxide film over time and normal handling can contaminate the surfaces with
finger oils and slight corrosion. A good
practice to follow is vigorous scrubbing
with a gentle abrasive such as a
Scotchbrite pad followed by cleaning
with rubbing alcohol or other non-aque-
SOP Receiver Assembly Manual, rev B
Top Half
5-1/4 b
c 5-1/4
Bottom Half
“SOP” 80m/40m CW Receiver
SOP Receiver Assembly Manual, rev B
ous solvent. Once cleaned this way the
copper should stay clean enough for several days so long as you keep it dry and
don’t handle it any more than necessary
during assembly.
As with any soldering operation, the
proper iron and amount of heat should
be used. Generally any soldering iron suitable for electronics use with a 35 to 50
watt rating is fine. 600-deg to 800-deg F
should do the trick if you are using a temperature-controlled solder station. Irons
with less wattage will not have enough
heat capacity to produce good joints while
higher-wattage ones can overheat the adhesive that holds the copper onto the
printed board base layer causing delamination. A flat chisel tip is preferred over
a cylindrical or conical one so that enough
heat can be transferred to the solder as a
running seam is made.
A good quality rosin core solder is fine
though some of the more modern “nowash” type mixes are good too. Do not
use acid core solder as it will destroy your
soldering iron tip and eventually lead to
severe corrosion of the copper surface of
the enclosure you are building.
Since you want the top and bottom of your
enclosure to fit snugly without unsightly
gaps or seams, alignment of the pieces
while you are soldering is quite important. Copper clad board boxes have their
individual sides joined together at right
angles. Accuracy in aligning each piece
accurately is what makes the enclosure
go together properly and look attractive.
A simple alignment gauge is included
with the enclosure kit to help you make
good right-angle joints. It is accurately
cut on at least one corner for perpendicularity (love those big words!). It is a good
idea to check all four corners against a
machinists or carpenter’s square to see
which one is best. You may also care to
use a file to “knock off” 1/8 or so on the
exact corner so that it will fit flush against
a corner of your box after soldering to
ensure “squareness” in the finished product. This will also let you know at as
glance which is the best corner! Using
the gauge will be described in the detailed
assembly steps so that the enclosure
pieces can easily be aligned the correct
Finally, you need a good clean uncluttered work surface! That should be obvious, but it is important. When working
with the pc board material, a fairly benign surface is necessary to keep the copper on the pc board material clean and
scratch-free. A soft cloth or towel laid out
on the table surface is best but in a pinch
you can use cardboard or newspaper. A
side benefit of using an overlay on you
work bench is that you will help protect
that surface as well as that of the project
you are working on. Eliminating clutter
helps you keep track of all the parts.
Ok, the preliminaries are out of the way
so let’s get started! Heat up your iron kick
the kids and pets out of your workshop
and turn on your rig so that you can be
soothed by the sound of cw on 7040 as
you work.
If you have already inventoried the parts,
great! If not please go back to the Package Contents section on page 3 and do
so. Select pieces a, b and c to build the
case top first.
Please refer to “Figure 3: Top Half Assembly” drawing on the next page. Note
from the end view that the two side pieces
b and c will be assembled to the inside of
top cover panel a rather than alongside
it. If the sides are soldered alongside the
cover, the cover will not fit on the bottom properly. Also observe that the top
cover is longer than it is wide so that the
longer side of pieces b and c will be
against the long dimension of a. Be aware
SOP Receiver Assembly Manual, rev B
Figure 3: Top Half Assembly
Case screw hole
FIG 5: Completed Top Half
SOP Receiver Assembly Manual, rev B
Figure 4: Use of Alignment Gauge
that the side view is shown upside-down.
When the case is finally assembled the
“overhang” will be at the top of the enclosure front panel. All right, that’s
enough visualization.
Lay piece a on the workbench and set one
of the side pieces (either one) on top of it
along one side. Line the side piece up
flush with the edge of the top cover, using the alignment gauge to ensure that the
two pieces are lined up at right angles.
The photo in Figure 4 demonstrates how
this is done. [Note: The one photo we
have of using the alignment gauge technique actually shows its use in soldering
the side rails to the base (described in
the next pages); but the technique is the
same as used in soldering the top half
sides.] It may seem awkward at first since
you have only two hands but you have to
do it with only one hand since you will
need the other for soldering!
Carefully load some solder on your soldering iron top and place a solder “tack”
in the middle of the seam between the side
and top pieces to hold it in place. Now
add a couple more tack joints about ½
inch or so from the front and back edges
while holding the pieces together with the
alignment gauge. When complete, the
side and top covers should be accurately
at right angles. Check along the seam
from front-to-back and carefully redo the
tack joints as needed to get the proper
Once you are sure of correct alignment
you can complete the solder seam. You
have two choices here. If you are cautious and don’t want extra bother, don’t
run the seam all the way out to the front
and rear edges of the cover. That is, keep
them back about 5/16 inch from the front
face of the side pieces and about 1/8 inch
from the rear face. If you are adventurous, run the seam all the way out. This
will require a little filing on the bottom
cover later, but will give you a somewhat
stronger box. To make the continuous
SOP Receiver Assembly Manual, rev B
Figure 6: Bottom Half Assembly
Case screw hole
view from
Right (or left)
Side View
seam, start at the back end of the seam
and slowly add solder to the joint as you
move the soldering iron along the seam.
Take care not to disturb the right-angle
that the cover and side piece make with
each other.
Now that you are an accomplished expert, repeat the above process with the
other side piece. You now have a completed top cover! It should look like the
photo in Figure 5.
Bottom Half Assembly
Next you will assemble the bottom cover.
Begin by identifying bottom cover d front
panel f and rear panel e. You can tell the
front and rear covers apart by noting that
the front panel has three holes while there
are four on the rear.
Examine Figure 6, the Bottom Half Assembly drawing, as illustrated on the next
page. It shows that the front and rear panels mount on the outside edges of the bottom cover and the side rails go between
the end panels inside the whole shebang.
We’ll first solder both side rails (parts g
and h) to the base plate (part d). By placing the smaller, less-critical side rails in
place first, the later step of soldering the
front and rear panels in place will be made
much easier.
Using the alignment gauge exactly as
shown previously in figure 4, solder one
side rail in place using the tack-first,
seam-solder second technique already described. The side rails are identical and
can be used interchangeably. Make sure
the edges of the side rail are even with
the front and rear edges of the base plate,
as this flush right angle edge will be the
mounting datum for the front and rear
panels. Don’t worry if the side rail is not
exactly even with the base plate, as you’ll
have a chance to “square things up” with
the flat file before putting the front/rear
panels in place.
Next, solder the second side rail in place
in the same manner as you did for the
first one. Now is the time to file the edges
to ensure flush perpendicularity.
You next solder the front panel (part f)
SOP Receiver Assembly Manual, rev B
onto the bottom plate (part d). Ensure
that the front panel is aligned square and
flush with the base/rail assembly. Hold it
in place with the claw grasp of one hand
as you tack solder several points along
the joint. Use the same solder-tack technique as you did for the top cover then
run a continuous joint in the seam after
ensuring proper alignment.
Repeat the same process to solder the
rear panel e to the bottom plate d.
off the sharp corers on the front and rear
panels so to clear the top-cover bead. See
Figure 8. You only have to “knock off”
about 1/16 inch so don’t get carried away!
When you are sure that the covers nest
together properly, put in the two sheet
metal screws that hold the top and bottom halves together. The first time that
you screw one of the screws into place, it
will be a hard turn on the screwdriver.
You’re coming along nicely now! Your
completed bottom assembly should look
something like that shown in Figure 7.
It’s a good idea at this point to fit the top
cover over the bottom to be sure that
everything fits. It should be a snug fit but
not so tight that you will stress the top
cover when it is installed. If you ran the
solder bead all the way out on the top
cover you will find that it interferes with
the edges of the front and rear panels.
Never fear – we’ll take care of that next.
Figure 8:
Fitting Top Cover
If you have continuous solder beads out
to the front and rear panels on your top
cover it is now necessary to perform a
small amount of cosmetic surgery. File
Figure 7: Completed Bottom Half
SOP Receiver Assembly Manual, rev B
This is because you are cutting threads
into the pcb material on the side rails. But
once you have these threads in place, insertion and removal of the screws should
be much easier to do.
Do not overtighten these screws! If you
are careful in tightening they will last for
many on and off cycles. If you inadvertently strip one out by over-tightening,
drill out the top cover screw holes and go
to the next larger size sheet metal screw!
The pc board edges and corners of the
assembled enclosure are sharp and rather
abrasive. You may care to bevel them to
protect your fingers and keep the box
from damaging tabletops and anything
else it comes in contact with. A couple
of swipes with a flat file will do the trick.
Early samples of case like this had a nasty
tendency to poke holes in bags and knapsacks before being refined this way!
Figure 9 below is a photo of the bottom
of a complete enclosure with the side
screws in place. Note the flush and even
nature of all pc board edges.
At this point you have a completed enclosure! All that remains is to do some
final finishing as you see fit and to install
the SOP Receiver and associated hardware.
Painting is a personal thing. While some
care to leave a “natural” copper finish,
others want to personalize their projects
by painting them outrageous colors or
match them to other equipment they may
have. The whole process is beyond the
scope of this manual but here are a couple
of tips.
1) If you are going to paint your enclosure be sure that all soldering is finished.
The heat from soldering inside the case
will conduct through the wall and damage your nicely painted surface.
2) Surface preparation is very important
to ensure that the paint adheres properly.
Use a Scotchbrite pad to remove surface
roughness and clean the metal immediately prior to painting with acetone, working in a well-ventilated area so that you
don’t suffer respiratory distress.
Figure 9: Completed Enclosure Bottom View
SOP Receiver Assembly Manual, rev B
Figure 10: Rear Panel with Labels
3) For a well-preserved “natural” copper
finish that will not tarnish use a clear
acrylic spray such as Krylon ™ clear
4) Other spray-on acrylic colors will work
okay for the short-term but may have a
tendency to chip or get scratched in time.
An oil-based paint like Rustoleum adheres well and gives a tough finish.
5) Chose a light color if you are going to
use the acetate overlays provided with the
kit. The lettering on them is black, but
may not have much contrast against a
dark surface.
Acetate labels are provided in your Enclosure Kit to help you create a neat and
professional-looking project case. These
clear overlays are pre-printed but do not
have holes cut in them for panel-mounted
controls and connectors. Once in place
on the panels, a sharp hobby knife such
as an Xacto knife will cut holes in the
appropriate control/jack locations quite
nicely. A good treatise on labels is
“Homebrew Chassis and Panel Labels”
by Ed Roswell, K2MGM. It appeared in
the Winter 2000 issue of the QRP
If you choose to use the acetate labels
provided in this kit, merely cut each one
out carefully along the outside of the rectangle defining the panel perimeter. This
will allow the rectangle to be present on
the panel when complete.
Next, spray adhesive or apply a light coating of rubber cement on the panel and
carefully position the acetate label sheet
over the panel and press into place. In a
few minutes, the adhesive will be dry and
you can delicately cut out the holes in the
acetate over the control/jack holes of the
panel. (Trick: Let the panels dry thoroughly, or even wait overnight, and the
holes will be easier to cut.)
It’s a good practice to lightly spray the
front of the acetate label with clear acrylic
like Krylon. This will protect the black
toner (comprising the actual labels) from
inadvertent scraping.
See Figure 10 above showing the rear
panel with labels applied. The front panel
labels are shown in the photo on the cover
of this manual.
See Figure 14 at the end of this section
for actual-size graphics used to create the
acetate labels. If you need to make an-
SOP Receiver Assembly Manual, rev B
other set of labels, you can run that page
through a copier using transparency material instead of paper in the copier.
All that needs to be done now is the finishing touches.
Rubber Feet - Carefully peel off the
black rubber feet supplied in the strip and
apply one each to the bottom side of the
enclosure. Make sure they are aligned
orthogonal and uniformly for maximum
esthetics. (That is, put them neatly in
place!) If the surface of the pc board material is clean, the rubber feet should stay
in place for a long while.
Put the top half of the enclosure on the
bottom half and secure it using the two
previously-used screws.
Now that your enclosure is all assembled,
painted and labeled, all that needs to be
done is to install the SOP circuit board
and control hardware.
The SOP Receiver board will be supported by four nylon standoffs, secured
by small #4 sheet metal screws.
attach a nylon spacer to the bottom side
of the board at each of the four holes on
the SOP board. The screw will be inserted
from the top side and protrude down and
into the nylon spacer on the bottom of
the board. You’ll be cutting threads into
the spacer, and it will be a tight turn of
the screwdriver. Hold the spacer tightly
with your pliers and turn the each screw
down into its respective spacer until the
board is tightly contained between the
screw and spacer on each end of the
board’s rear edge.
Next, carefully insert the board assembly into the enclosure and position it over
the four holes in the base plate. Using the
same technique as above, screw four #4
sheet metals screws (supplied) through
the bottom of the case and up into the
four nylon standoffs on the board. If the
holes do not perfectly line up, try loosening the top side screws and let the nylon
washer float into the correct position
when screwing the bottom screw in place.
Worst-case, if the holes cannot be made
to line up, just use 2 or 3 screws on the
bottom, and the board will still be held
securely in place.
Using small sheet metal screw (supplied),
SOP Receiver Assembly Manual, rev B
he’s also fabricating an entire, modular,
multi-board inner structure out of the copper clad boards. Homebrewing boundaries have officially been extended to the
SOP Receiver Assembly Manual, rev B
“SOP” 80m/40m CW Receiver
If you have any questions or problems
with the enclosure aspects of this project,
please feel free to contact us by email or
by US ground mail. We’ll do our best to
help you fully enjoy all aspects of your
homebrew enclosure.
This method of homebrewing project enclosures is bound to be growing in the
future. Opportunities for modifications
and personal customizations are limited
only by your imagination. One of our
members of the NJQRP Club has a project
in progress wherein he is making the enclosure for his 2N2/40 Transceiver completely out of pc board material, just like
with this basic SOP design. In addition,
A view of the Rear Panel Jacks
A View of the Front Panel Controls
SOP Receiver Assembly Manual, rev B
Section 4:
SOP Controls Option
Assembly Manual
This optionally-purchased Controls & Hardware Kit is another “ideal
companion” to the basic SOP Receiver. All of the front panel controls
and rear panel jacks are provided to enable the homebrewer to quickly
and easily bring his SOP Receiver to a working state. These controls
mate perfectly with the Enclosure Kit (another optional purchase) to
form the completely operational receiver.
This will be an easy accessory kit to deal
with. What you’ll do is wire the controls
and jacks to the board as shown in the
figure on the next page.
Parts Inventory
The first thing to do is to compare the
contents of the little plastic bag containing the controls and jacks to the Parts List
shown on the next page. Make sure everything is present before you begin.
Carefully remove the nuts and washers
from the two 1/8” jacks, the coaxial DC
power jack, and from the RCA phono
jacks. Install each into its respective location on the front and rear panels of your
favorite enclosure. If you haven’t yet selected or prepared your enclosure, you
may of course just wire these parts directly to the board and leave them hanging in “free space” off the end of the connecting wire
Using short insulated hookup wire, thin
RG174 coax cable, shielded audio cable,
or whatever other wire you might have
handy in your junk box, connect the
ground and signal/power wires of each
component to the respective pads along
the edge of the circuit board.
J3 3.5mm jack -- The ground terminal
on this PHONES jack is the little one on
the side, and the signal terminal is the
larger one on the opposite side.
J4 coaxial DC power jack -- The ground
terminal is middle one, and the +V terminal is the one on the left. (The right
terminal is unused.) Wire the +V terminal over to the switch on the Audio potentiometer. (See that section below.)
Wire the ground terminal directly to the
pcb pad for GND, next to the +V pad.
J1, J2 phono jacks -- The ground terminal of these is the tabbed washer (bend it
slightly up and away from the case in order to solder the ground wire to it.) The
signal wire should be attached to the center terminal of the phono jack. Wire one
of the phono jacks to the KEYLINE pad,
with its corresponding ground wire going to the GND pad next to the KEYLINE
pad. Wire the other phone jack to the
ANT pad on the pcb, with its corresponding ground wire (or shield of the thin coax
used) to the GND pad next to the ANT
R24 Audio Potentiometer -- This pot
also contains the power switch, so wire
the 2-tabbed side of this control between
the power jack and the +V pad of the pcb.
Wire the 3-terminal pot tabs to the pcb as
shown in the diagram.
SOP Receiver Assembly Manual, rev B
De signator
J1, J2
P1, P2
De scr iption
RCA Phono jack, nickel plated, ground, black insulator
DC pow er jack, 2.1mm, molded, economy, w ith NC sw itch
Black plastic knob w /blue top, .25" shaft
DC pow er plug, 2.1mm x 5.5mm x 9.5mm black locking, barrel
RCA phono plug, black plastic insulator, hollow center pin
Audio pot , 10K-ohm miniature potentiometer w /sw itch
Tune pot, 50K-ohm miniature potentiometer
Pushbutton sw itch, normally open, momentary contact
3.5mm jack, black, panel mount
R9 Tune Potentiometer -- This pot is
just a pot. Wire its 3-terminal tabs to the
pcb as shown in the diagram.
Front Panel Knobs -- Using a small flat
blade screw driver, partially unscrew the
set screw from each knob until they are
able to be slipped onto the shafts of the
potentiometer controls. [The following
applies if the pots are already mounted in
a front panel.] With each pot shaft turned
completely counterclockwise, rotate the
knob (which is still loose on the shaft)
such that its indicator is pointing to the
seven o’clock position and tighten the set
screw. This will give the pot and knob
normal relative indications during operation.
PB1 pushbutton -- This little red-topped
pushbutton is used as the SPOT switch
for the Audio Frequency Annunciator
option. When pressed, it triggers the
FreqMite microcontroller to sound the
current frequency through the PHONES
jack. (We figured that most people would
be interested in the AFA option; but even
if not, this pushbutton would nicely fill
the front panel hole!)
Extra Plugs -- In a further attempt to ease
the job of getting your SOP Kit operational, we’ve included the mating plugs
to some of the jacks on the rear panel.
Two phono plugs (P1, P2), and a coax dc
power plug (P4) are included to allow you
to wire up the mating cable for the antenna, keyline and dc power.
SOP Receiver Assembly Manual, rev B
Section 5:
Test & Measurement
Here are two simple circuits that can be effectively used to get your
SOP Receiver into tip-top shape. The first is a great little audio oscillator contributed by Joe Everhart, N2CX. With this useful gem you’ll
be able to inject low-level signals into your audio chain and trace them
through to the speaker. The other circuit is a standard-but-nifty RF
Probe, contributed by Chuck Adams, K7QO as part of his series of
articles concerning “Manhattan-style construction techniques”, published in QRP Homebrewer. With the RF Probe you’ll be able to measure the signal coming from your local oscillator, the LO buffer and
other RF signal sources. Very handy indeed!
Twin-Tee Audio Oscillator
by Joe Everhart, N2CX
This circuit is an old favorite of mine. It
was the very first Joe’s Quickie in the
QRP Quarterly’s Information Exchange
column and is still a favorite on the N2CX
workbench. Though very simple, this circuit is an excellent signal source for debugging and troubleshooting.
Power is supplied by a 9-volt battery (a
carbon-zinc “cheapie” is fine) and the
output is a 1 KHz sine wave. A simple
resistive divider from the transistor collector reduces the output to about 1 mV
while the 0.47 uF capacitor provides DC
isolation. Check the original article for a
table of resistor attenuator, which set the
output levels.
It’s a pretty non-critical circuit that can
be built ugly or beautiful. I built mine on
a scrap of perf board. There is no power
switch; to turn it on I simply clip a 9volt battery onto the power connector.
And there’s no fancy output connector,
either. An output and ground lead are
wrapped over the edge of the board for
access to a clip lead or soldered-on wires.
500 Hz
~ 1 mV
SOP Receiver Assembly Manual, rev B
Building an RF Probe
by Chuck Adams, K7QO
The first thing to build is an RF probe.
Go to the ARRL Handbook to page 26.9
and look at figure 26.9(C) for a voltage
doubler circuit. Don’t use the entire circuit. All you need is C1, C2, D1, and D2.
The AC input will be the RF signal and
the point at which D1 and C2 meet will
be the +DC output. Eliminate R1 and R2
from the circuit. The values here are not
too critical and you can experiment with
this. Use something like 0.1uF or smaller
for C1 and something like 0.47uF or
larger for C2. For D1 and D2, use either
germanium or silicon diodes. I used some
surplus printed circuit board leaded diodes that I got surplus somewhere and of
type 1N4148 or 1N914 silicon diodes.
I won’t go into the nitty-gritty details here,
but you need three pads and just a small
segment of printed circuit board. Because
the leads were short I mounted the diodes
horizontally. D1 is between two pads. D2
is soldered to the center pad and the other
lead soldered to the ground plane. With
longer leads you can mount the diodes in
a vertical position. The probe will work
the same with either configuration.
I have a Ballantine RF probe that I purchased for $10 at a Livermore Swapmeet
on a trip to CA when I was working. This
probe came sealed in an aluminum pouch
with all kinds of military part numbers,
etc. Probably cost the tax payers a few
hundred dollars. I compared my readings
with the RF probe built Manhattan-style
and the Ballantine probe and got the same
results to over 40MHz. The one here
probably cost me about a quarter. The
commercial probe is nice, but not everyone can find such a great deal. Besides,
in the building of homebrew gear you can
take extra pride in using something that
you personally built and can repair.
Your VOM should be set for DC volts,
and your reading will then be RMS volts,
or Vrms = Vpeak * 0.707.
To cir cuit
meas ured
SOP Receiver Assembly Manual, rev B
SOP Receiver Assembly Manual, rev B
SOP Receiver Assembly Manual, rev B
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