Ramsey Electronics | STC1 | Instruction manual | Ramsey Electronics STC1 Instruction manual

Ramsey Electronics Model No.
Own and operate your own FM Stereo broadcast station.
Definitely not a toy, the FM-10A has an exceptional transmission
range... and the audio quality puts your favorite radio station to
shame. See why this is one of our most popular kits!
Great for transmitting your tape deck or CD player throughout the
house, yard or even your car.
Powerful enough for college or neighborhood radio stations - in
use all over the world.
Fantastic audio quality sounds better than most stations on the
dial. And we’ll tell you why!
Easily connects to the line-level outputs on any tape deck, stereo
system or CD player.
Some users hook up one channel to the scanner and the other to
their two way radio. Now you can hear what’s going on around
town up to several blocks away from your house with a simple
stereo receiver... and adjust the volume of each individually with
your balance control!
Add a mike-mixer and tape or CD deck for a “PRO” sounding radio
Operates on 1.5 to 15 volts, using a crystal controlled subcarrier.
Tunable anywhere in the 88-108 MHz FM band.
Clear, concise instructions guide you step by step.
• FM25, MP3FM FM Stereo Transmitters
• AM1 AM Transmitter
• TV6 Television Transmitter
• FM100 Professional FM Stereo
• FR1 FM Broadcast Receiver
• AR1 Aircraft Band Receiver
• SR2 Shortwave Receiver
• AA7 Active Antenna
• SC1 Shortwave Converter
• SG7 Personal Speed Radar
• SS70A Speech Scrambler
• MX5, MX-10 Mixers
• MD3 Microwave Motion Detector
• PH10 Peak hold Meter
• STC1 Stereo Transmitter Companion
• FX 146 VHFTransceiver
• HR Series HF All Mode Receivers
• QRP Series HF CW Transmitters
• CW7 CW Keyer
• CPO3 Code Practice Oscillator
• QRP Power Amplifiers
Many other kits are available for hobby, school, scouts and just plain FUN. New
kits are always under development. Write or call for our free Ramsey catalog.
Ramsey Electronics publication No. MFM10A Revision G
First printing: August, 1994
COPYRIGHT 1994 by Ramsey Electronics, Inc. 793 Canning Parkway, Victor, New York
14564. All rights reserved. No portion of this publication may be copied or duplicated without the
written permission of Ramsey Electronics, Inc. Printed in the United States of America.
Ramsey Publication No. MFM10A
Manual Price Only: $5.00
Introduction to the FM10A ....................................... 4
FM10A Circuit Description ....................................... 5
Schematic Diagram ................................................. 5
Parts List ................................................................. 6
Parts Layout Diagram .............................................. 7
Assembly Instructions ............................................. 8
Choosing an Operating Frequency.......................... 13
Adjusting your FM10A ............................................. 14
Using your FM10A Within the Home ....................... 15
Power Supply Considerations ................................. 15
LED Power On Indicator .......................................... 15
Experimental Broadcasting Projects........................ 16
Antenna Ideas ......................................................... 17
Troubleshooting Guide ............................................ 18
Appendix A: FCC Rules and Information ................. 19
Appendix B: Understanding Field-Strength ............. 22
Summary ................................................................. 24
FM10A Kit Warranty ................................................ 27
793 Canning Parkway
Victor, New York 14564
Phone (716) 924-4560
The Ramsey FM10A is a true STEREO FM broadcast transmitter, which
any person may build and use in accordance with the rules of your nation’s
telecommunications authority. For U.S. residents, that authority is the
Federal Communications Commission (FCC). The FM10A's low-power
broadcasting capability and other practical uses can be fun and interesting
for people of all ages, but the FM10A is definitely not a toy. We will refer to
the FCC regulations frequently in this manual and provide you with some
information necessary to enjoy the FM10A's capabilities in accordance with
the law.
Typical uses for the FM10A include the following:
Extension of home stereo system - without wires.
Listening aid for auditoriums, churches.
Student-operated school radio station.
College dorm favorite music broadcast service.
Short-range, two-channel experiments and demonstrations.
We think you will be very pleased with the transmitting range, audio quality,
frequency stability and stereo channel separation of this build-it-yourself FM
stereo transmitter. If you follow our assembly directions carefully and use
your FM10A in accordance with applicable FCC rules, a whole new world of
sharing music, news and views with friends and neighbors awaits you.
Since the sharing of music and information is vital to the culture of our late20th-century global community, we realized that our FM10A low-power FM
Stereo Transmitter kit was certain to attract worldwide interest among
hobbyists, students and "pioneers." While the use of the FM10A may need
to be limited to "wireless stereo extensions" in some USA households (to
comply with FCC Rules, Part 15), we have seen it serve very well as a
serious, though simple, broadcast station for remote villages throughout the
world where low cost AM-FM receivers are available to people of all
economic levels. After you're done building your kit, sitting back and
listening to your handiwork, consider this: many other FM10A's just like
yours are faithfully relaying news and information to listeners in remote parts
around the world. The FM10A is most definitely not a toy!
A quick glance at the Schematic Diagram shows that the custom FM
stereo transmitter IC (U1) is at the heart of the FM10A. The control of U1 is
determined by its surrounding circuitry. Potentiometers R1 and R4 allow for
adjustment of input level. Resistors R3 and R6 set the pre-emphasis
characteristics (75uS for USA and 50uS for Europe). R7 permits adjustment
of stereo balance. L1 and C16 form an adjustable resonant circuit to set the
carrier operating frequency. Diodes D1,2 and 3 regulate the voltage to U1 at
2.1 volts DC, though Q1 may be operated safely up to 12-15 VDC. The RF
output of Q1 feeds both the on-board whip antenna and J3 for an external
ˆ 4 10 pf disc capacitor (marked 10 or 10K) (C7,8,14,15)
ˆ 1 18 pf disc capacitor (marked 18) (C16, see note below)
ˆ 1 22 pf disc capacitor (marked 22) (C16, see note below)
ˆ 1 27 pf disc capacitor (marked 27) (C16, see note below)
NOTE: Selecting 18, 22 or 27 pf for C16, establishes the FM-band
frequency adjustment range. See “Choosing an Operating
ˆ 1 220 pf disc capacitor (marked 220 or 221) (C9)
ˆ 8 .001 µF disc capacitor (marked .001 or 102 or 1 nf)
ˆ 2 .0047uF disc capacitors (marked 472) (C1,4)
ˆ 4 4.7 to 10 µF electrolytic capacitors (C2,3,5,11)
ˆ 1 470 µF electrolytic capacitor (C19)
ˆ 1 1000 µF electrolytic capacitor (C22)
ˆ 2 270 ohm [red-violet-brown] (R9,R13)
ˆ 1 470 ohm [yellow-violet-brown] (R8)
ˆ 1 4.7K ohm [yellow-violet-red] (R11)
ˆ 3 10K ohm [brown-black-orange] (R3,R6,R10)
ˆ 2 15K ohm [brown-green-orange] (R3,R6)
ˆ 1 150K ohm [brown-green-yellow] (R12)
ˆ 1 100K yellow trimmer potentiometer (marked 104) (R7)
ˆ 2 1K yellow trimmer potentiometer (marked 102) (R1,R4)
ˆ 3 Glass bead diodes (similar to 1N4148) (D1,2,3)
ˆ 1 2SC2498 or 2570 NPN VHF transistor (Q1)
ˆ 1 18-pin DIP Custom FM Transmitter integrated circuit (U1) with
matching socket
ˆ 1 38 KHz crystal (small silver cylindrical "can" with 2 small leads), taped
to a piece of paper.
ˆ 1 Shielded inductor coil (L1) (small square silver “can”)
ˆ 1 Ramsey FM10A Printed circuit board
ˆ 1 Plastic alignment screwdriver
ˆ 1 PC board mounted push-button switch
ˆ 3 RCA-type PC-mount jacks (J1,2,3)
ˆ 1 2.5 mm phone jack (J4)
ˆ 1 9-volt battery hold-down clamp
ˆ 1 9-volt battery snap connector
ˆ 9-volt alkaline or heavy-duty battery
ˆ Shielded stereo audio cables
ˆ Line-level output audio source (such as a tape deck or CD player)
ˆ External antenna, small gauge coax and RCA plug, OR PC board
mounted telescoping whip antenna (included with the Ramsey CFM
case and knob set.
ˆ Ramsey FM10A case and knob set (CFM), or your own enclosure
ˆ LED "power on" indicator and 1K resistor
ˆ Audio switching-mixing accessories of your choice
Building your FM10A Stereo Transmitter
The following FM10A step-by-step assembly and adjustment directions are
written with newcomers in mind. While many Ramsey kits are purchased by
experienced hobbyists and ham radio operators, our instructions presume
that this stereo transmitter could be your first ever kit project.
Ramsey Electronics Kit instruction manuals are designed around our
"Learn as You Build" philosophy. To the extent that it is reasonably possible,
we like to help you see why a given part goes into its PC board holes, as well
as showing you how to do it. Our "Learn as You Build" assembly strategy
works very well with our simpler kits, such as receivers and ham
transmitters, where we can guide you through the schematic diagram from
the antenna to the speaker. When a multi-function IC "chip" is the heart and
soul of one of our kits, as is the case in this FM10A stereo transmitter, we try
to make a reasonable compromise between following the signal path and
just getting all parts in properly so you can enjoy your kit as soon as
So, you can expect the following directions to be a nice blend of "Learn as
You Build" and "Let's get these parts in right and as quickly as possible!"
First assembly steps
Use the boxes to check off your progress.
ˆ Check all received parts against the Parts list on page 6. The parts list
describes the various markings that may be found on the kit parts.
Since you may appreciate some "warm-up" soldering practice as well as a
chance to put some "landmarks" on the FM10A PC board, we'll first install
some "hardware" components, to make the up-down, left-right orientation of
the PC board as clear as possible.
In ALL the following instruction steps, our word "INSTALL" means this:
Insert the part, oriented correctly, into its correct holes in the PC
If helpful, gently BEND the part's wire leads or tabs to hold it in place,
with the body of the part snugly against the top "component
side" of the PC board.
SOLDER ALL wires or pins of the part, whether the two wires of a
resistor or the 18 pins of an IC socket.
Nip or "trim" all excess wires extending beyond each solder
connection, taking care that wire trimmings do not become lodged in
PC board solder connections.
Enough said. . . Let's get building!
ˆ 1. Install S1, the DPDT push-button switch. It fits correctly only one way.
Ensure that the white plastic switch extends out over the edge of the
printed circuit board. Solder all six pins.
ˆ 2. Install J1, the Right Channel input jack. Solder all 4 points of the jack
ˆ 3. Install J2, the Left Channel input jack. Solder all 4 points of the jack
ˆ 4. Install J3, the RF output (antenna) jack. Solder all 4 points of the jack
ˆ 5. Install J4, the 2.5 mm phone jack (external DC input). Solder all 3
ˆ 6. Install the 18-pin DIP socket supplied with your kit. There is no right
or wrong direction to this socket, but the U1 IC itself certainly needs to
be inserted correctly (later). Taking care of this socket early in the
project will help you with positioning additional parts and will fine-tune
your soldering technique. Before soldering, make sure the socket body
is flush against the PC board, and that all 18 pins have been inserted.
Solder all 18 pins and then CAREFULLY check to ensure you have not
caused any "solder bridges" between pins.
ˆ 7. Now that the IC socket has your prime attention, carefully insert the
FM transmitter IC (U1) into the socket, taking gentle care that ALL 18
pins get into their proper holes. The orientation of the notched end, as
shown on the Parts Layout Diagram is critically important.
Progress Note: The preceding steps have secured a sufficient number of
components to your PC board to make general orientation around the board
much clearer for installing additional parts. Further parts will be installed in
three phases or groupings.
Wiring the audio input circuits
We encourage you to peek at the schematic diagram and learn the
functions of the following parts. However, the sequence of installation is in
the order of convenience and speed. If you wish, insert the parts groupings
as one operation, then solder and nip all connections.
ˆ 8. Install R1, one of the small yellow trimmer potentiometers marked
"102". Don't confuse it with R7 which is marked "104".
ˆ 9. Install R4, the other yellow trimmer marked "102". These two
trimmers will allow you to adjust the input level.
ˆ 10. Install C1, .0047 µF (marked .0047 or 472). If you are building your
kit for use in North America or Japan, resistors in steps 11 and 12 are
installed as printed. For use in Europe, Russia and some other
countries, use 10K ohm resistors in steps 11 and 12. These resistors set
the pre-emphasis characteristics for the FM10A. Pre-emphasis is a
technique used in FM transmitters to increase the high frequency signal
to noise ratio. If you desire a "brighter" sound you may use the 10K ohm
resistors rather than the 15K ohm parts.
ˆ 11. Install R3, 15K [brown-green-orange].
ˆ 12. Install R6, 15K [brown-green-orange].
ˆ 13. Install C4, .0047 µF (marked .0047 or 472).
Electrolytic capacitors have a right and wrong way to be installed. Usually,
capacitors have a black strip which indicates their ( - ), negative lead and the
PC board or Parts Layout Diagram will show the ( + ), positive side of the
capacitor's installation hole. Be sure to place the ( + ) capacitor lead into the
PC board ( + ) hole and the ( - ) lead into the ( - ) hole. Observe correct
polarity when installing the following three electrolytic capacitors:
ˆ 14. Install C2, 4.7 or 10 µF. Don’t forget... the proper orientation is noted
on the PC board or Parts Layout Diagram.
ˆ 15. Install C5, 4.7 or 10 µF. Observe correct polarity.
ˆ 16. Install C3, 4.7 or 10 µF. Remember correct polarity.
Diodes also have a right and wrong way to be installed. The cathode
(banded) ends face toward the outside of the PC board, away from the IC
circuitry. Observe correct polarity when installing the following three diodes.
ˆ 17. Install glass bead diode D1.
ˆ 18. Install glass bead diode D2.
ˆ 19. Install glass bead diode D3.
ˆ 20. Install R7, the small yellow trimmer potentiometer marked "104".
ˆ 21. Install C19, the 470 µF electrolytic. Be sure to position for correct
ˆ 22. Install C11, 4.7 to 10 µF electrolytic. Observe polarity.
ˆ 23. Install R11, 4.7K [yellow-violet-red].
ˆ 24. Install R12, 150K [brown-green-yellow].
ˆ 25. Install C9, 220 pf [marked 220 or 221].
ˆ 26. Install C10, .001 µF [marked .001 or 102 or 1nf].
ˆ 27. Install C22, the large 1000 µF electrolytic capacitor. Observe
ˆ 28. Install R8, 470 ohms [yellow-violet-brown].
ˆ 29. Install C20, .001 µF (marked .001 or 102 or 1 nf).
RF amplifier and final components
ˆ 30. Install shielded slug tuned coil L1. The larger tabs secure the shield
can to the ground foil connections, while the two thin leads are the coil
connections. If you find that the coil lead wires do not line up with the
PC board holes, simply "pull" the coil insert from the shield can, rotate it
a quarter-turn and insert back into the can. Make sure L1 is squarely
against the top of the PC board before soldering, solid installation of L1
is essential to the frequency stability of your transmitter.
ˆ 31. Install C15, 10 pf (marked 10 or 10K).
ˆ 32. Install C14, 10 pf (marked 10 or 10K).
ˆ 33. Install R9, 270 ohms [red-violet-brown].
ˆ 34. Install C17, .001 µF (marked .001 or 102 or 1 nf).
ˆ 35. Install R10, 10K ohms [brown-black-orange].
The following two capacitors have the identical functions of coupling the RF
output from the collector of Q1 to the RF output jack (J3) and also the
mounting point provided if you wish to use an on-board whip antenna.
ˆ 36. Install C13, .001 µF (marked .001 or 102 or 1 nf).
ˆ 37. Install C21, .001 µF (marked .001 or 102 or 1 nf).
ˆ 38. The 3 holes for Q1, the 2SC2498 RF power amplifier transistor,
should now be quite clear. Press the transistor into place firmly but
gently, so that its body is as close to the board as reasonably possible.
Observe correct placement of the flat side.
ˆ 39. Install R13, 270 ohms [red-violet-brown].
ˆ 40. Install C12, .001 µF (marked .001 or 102 or 1 nf).
ˆ 41. Install C18, .001 µF (marked .001 or 102 or 1 nf).
ˆ 42. Install C6, .001 µF (marked .001 or 102 or 1 nf).
ˆ 43. Install C8, 10 pf (marked 10 or 10K).
ˆ 44. Install C7, 10 pf (marked 10 or 10K).
ˆ 45. Install Y1, the small silver "can" crystal. Be especially careful when
installing this part as its leads are very small. You may elect to put a
small "dab" of glue on the part to relieve stress and to keep it firmly
attached to the PC board.
ˆ 46. Install the battery snap connector (without battery); The red wire is
positive and the black wire is negative.
ˆ 47. Install the battery hold-down clamp, using a scrap component lead
wire looped through the PC board holes and soldered.
ˆ 48. OPTIONAL: If you purchased the Ramsey case, hardware and whip
antenna set, you may now install the telescopic whip. The antenna is
attached to the PC board at the hole labeled "WHIP" using the small
screw provided.
At this point, all PC board components except C16 have been installed.
Before proceeding, this would be a good time for you or a friend to doublecheck your work.
FM10A frequency range selection
Capacitor C16 sets the frequency range of the FM10A. Values for C16 are
as follows:
Desired Transmitter Frequency Range C16 Value
Lower end of FM band .......... (88-94 MHz) .... 27 pf
Middle portion of FM band ... (91-100 MHz) ... 22 pf
High end of FM band ........... (95-108 MHz) ... 18 pf
If you are not sure "where" you wish to place your FM transmitter in the FM
band, we suggest you solder an initial "trial" C16 capacitor with a small
amount of lead-length to spare, so that it is easy to salvage and replace.
This will enable you to properly test your FM10A and then at a later point,
you may change C16 as desired.
ˆ 49. Install C16, either: 18, 22 or 27 pf.
[A] It really is NOT sufficient to just "check" the FM band for an empty
frequency, using the FM portable radio closest at hand. It is your
responsibility to carefully research what FM stations can be listened to with a
good system within the transmitting range of your FM10A. This is especially
important in the low end of the FM broadcast band (88-92 MHz), where there
are numerous medium power National Public Radio stations perhaps outside
your own town, but which your neighbors may enjoy receiving, using a good
receiver and outdoor antenna. Interfering with such reception is a direct
violation of federal law. The most reliable way of finding a truly open
frequency on the FM band is to check the band with a very good FM
receiving system using an external antenna. If you do not have access to
such a radio, most modern car radios (with exterior antenna) are very
sensitive and usable to help you know what stations your neighbors really
can be receiving on a particular frequency.
[B] In choosing an operating frequency, remember that most "digital-tuning"
receivers, whether portable, mobile or hi-fi, are designed to tune in 200 KHz
increments and therefore might not receive well a signal operating between
these pre-tuned standard broadcasting frequencies. In order to comply with
Part 15 of FCC regulations, it is your responsibility to determine carefully that
your operation will not cause interference to broadcast reception. Please
study Appendix A of this manual before using your FM10A.
Keep all tests very brief until you have carefully chosen an open operating
frequency in the FM broadcast band.
1. Transmitting Frequency:
After finding a suitable "open" frequency in the 88-108 MHz FM band,
adjust L1 with the plastic alignment screwdriver until you hear the carrier
frequency on a nearby FM radio. No audio input is needed to make this first
adjustment, you can simply listen for a "quieting" in the normal background
noise "hiss."
2. Audio Connection:
Adjust both Left and Right level potentiometers (R1, R4) to full counterclockwise rotation. This is the minimum level position. Then increase them
slightly. The best audio input for both testing and general operation are the
stereo "line-level outputs" of a cassette deck or CD player. Most stereo
systems have a variety of auxiliary output jacks of which one or more are
line-level outputs.
Hooking up an audio source to your FM10A is really quite simple.
However, there are some general rules:
A terribly distorted sound is a sign of too much audio level. Simply
rotate the level potentiometers, R1 and R4, CCW to reduce the level.
Make sure you rotate each one about the same amount to maintain
proper stereo balance.
Stereo LP turntables are low-level output and will require the use of a
preamplifier for proper audio input to the FM10A.
NEVER connect the FM10A audio inputs to speaker outputs of a high
power stereo system; such a connection will destroy the IC chip.
Consider using a mike mixer for professional "radio station" sound. It
will allow you to easily fade, mix and switch between various audio
3. Stereo balance:
Adjust R7 for correct stereo balance. The better your ear for music and
your understanding of quality audio devices and interconnections, the better
will be the performance of your FM10A.
A most practical use for the FM10A would be to connect it to the main
stereo system within a large home so that whatever is playing on the main
system can also be tuned-in on portable FM radios in other rooms, the
garage or out in the yard.
This connection consists of using shielded audio cables to connect the
auxiliary "line audio" output of your cassette deck, CD player or other stereo
device to the audio inputs of the FM10A. Consult the literature that came
with your stereo equipment.
Even if you intend only this limited convenience use of the FM10A for your
own home and family, it is still your responsibility, in accord with Part 15 of
the FCC Rules, to ensure that this operation does not cause interference to
your neighbors.
The FM10A is designed to operate from a single 9-volt battery mounted on
the PC board. For prolonged operations, note from the schematic diagram
that replacing R8 with a jumper wire will permit operation from a 1.5V or 3.0V
DC source such as D cells. Diodes D1, D2 and D3 regulate the voltage to
U1 at 2.1 volts. Note, however that reduced voltage will also affect the
collector voltage and therefore the output power of Q1.
Whether an alternative AC adapter can be used depends on the quality of
the adapter and its ability to suppress unwanted AC-line hum. Various plugin adapters and power supplies in the 6 to 12 volt range may be tried, but
make sure the unit has DC output (positive tip) and is not merely a
transformer relying on rectifier circuitry within the device for which it was
originally supplied as an accessory.
Since the transmitter consumes power and emits RF whenever it is turned
on, a visual "on the air" indicator is desirable and is a fun enhancement of
your completed kit. If you are designing the FM10A setup for use by
youngsters, a flashing indicator is easily provided using our BL-1 "LED
Blinky" kit. Voltage for a standard LED is easily taken from the unused top
terminals of S1. The inner pin nearest the red lead of the battery cable is the
+9 volt pin. The ground can be taken from the black battery terminal, or the
case of any of the jacks, but it CANNOT be the antenna. This positive DC
must be connected to the anode (longer wire) of the LED. Use a 1K resistor
in series with either wire of the LED. The cathode lead is connected to the
negative battery wire. The resistor is omitted if you are using a 1.5 volt
battery for prolonged short-range operation.
To use the FM10A successfully as a "broadcasting" service to interested
listeners in a school or immediate neighborhood, most of your effort will be
concentrated on smoothly "managing" or mixing the audio signals fed into the
transmitter input. Operation of the transmitter itself consists simply of the
ˆ 1. Correct construction and adjustment.
ˆ 2. Carefully checking for an open frequency between 88-108 MHz in
accordance with FCC Rules, Part 15.
ˆ 3. Setting up a suitable antenna.
ˆ 4. Connecting the audio source to the Left and Right input jacks.
ˆ 5. Turn on the transmitter while you intend to be "on the air" and turn it
off when you are finished.
Explaining how to build a simple audio "mixing" panel or box, which is at
the heart of any studio operation, is beyond the purpose of this instruction
manual. We do recommend that you design and build this mixing system
yourself, for several reason:
1. Parts to do so are readily available at Radio Shack.
2. It would be an excellent class, family or Scout project.
3. Commercially-made stereo mixing consoles, while much less expensive
today than a decade ago, will cost much more than did your FM10A kit!
4. The more home-built your complete setup, the more it is in conformity with
the spirit of FCC Part 15 regulations.
If you are designing the FM10A and its mixing inputs to serve as an
educational and entertaining toy for your children, we suggest that the
FM10A PC board be incorporated with the mixing circuits into a durable, nonhazardous enclosure. If infants and very young children are likely to
"examine" this magical box when their siblings are not looking, it is better not
to use a whip antenna, due to the hazard of eye damage. Also, remember
that any broken whips from radios, cordless phones, etc. can become
dangerously sharp.
Although many sources exist for audio mixers, the Radio Shack No. 321105 is the least expensive commercial device currently available. Bear in
mind that specifications and model numbers for such accessory equipment
can change from year to year. Also, some home-entertainment audio
equipment includes simple mixing capabilities which will permit you to fade
and "cue" music and microphone inputs. Ramsey now sells the MX-5 and
MX-10 mixer kits (and wired and tested units!) and the Stereo Transmitter
Companion (STC-1) for a “radio station” quality home broadcasting set-up.
The simplest, yet very effective, antenna for the FM10A consists of a
"dipole", set up either horizontally or vertically, and connected to the
transmitter output jack through a few feet of coaxial cable (either RG-58, RG59 or miniature RG-174, available at Radio Shack and other sources).
Correct dipole lengths for major sections of the 88-108 MHz band are:
88 MHz, each side: 2.7 feet; 5.4 feet total
98 MHz, each side: 2.4 feet; 4.8 feet total
108 MHz, each side: 2.2 feet; 4.4 feet total
You can see that there is not a great difference in antenna length from 88 to
107 MHz. Some antenna designers have the view that an "approximate"
dipole such as 2.5 ft. on a side will do fine, while others believe it is worth the
effort to calculate the length for your exact frequency, using the simple
formula of Length (of one side, in feet) = 234/Frequency in MHz.
If the dipole is installed vertically, the end connected to the center conductor
of the coax should be the upper (higher) end. If young children will be around
the set-up, a flexible wire antenna is preferable, rather than rigid tubing.
A "ground plane" antenna can be quite effective. A ground plane consists
of one vertical element, the same length as one side of a dipole, connected to
the center conductor of the coax. Four "radials" are connected to the
shielded side of the coax at a 90 to 135 degree angle to the vertical element.
The dipole formula is also used to calculate the length of the radial; since
radials should be slightly longer than the main element, use 240 rather than
234 in your calculations.
If you are equipped to make the field strength measurements required by
Part 15 FCC rules, and if you think it would be best to aim or "focus" your
signal in a narrower direction, you can consult an antenna handbook and
design a suitable gain antenna. See Appendix A concerning FCC field
strength limitations. An FM- VHF TV receiving antenna could be modified for
such a purpose. Ramsey now has the TM-100 Tru-match FM broadcast
antenna, ideally suited for your FM10A
Ham radio books and magazines are filled with antenna principles and ideas
which can be adapted to your application. Also, you may wish to look at Radio
Shack book No. 62-1083 on antennas.
If your situation involves a single large building or multi-level home where
reception from the FM10A antenna tends to be uneven because of walls and
other VHF path obstacles, you might set up the FM10A's output in a "carriercurrent" configuration. If you know how to do correctly, then do so - safely. If
not, you can show your FM10A and this book to a licensed radio engineer and
negotiate with that person for a safe installation which will feed your signal
through interior wiring of your home or building. Do not attempt such an
installation unless you know exactly what to do and not to do. Also, because
such an installation is beyond the original purpose of this kit and the safety
standards intended for all Ramsey kits, and because we have not tested the
FM- 10A in such an installation, we cannot provide further details for such an
If your FM10A does not work at all, re-check the following:
correct orientation of U1 (see PC board parts layout diagram)
correct polarity of all electrolytic capacitors,
Correct orientation of diodes D1,2,3,
correct orientation of Q1 transistor,
correct value of C16,
all solder connections.
Frequency drift is usually caused by a weak battery or operation at large
temperature extremes.
Erratic or unstable operation is caused by faulty solder joints or cable
Standard 2SC2498 replacements: ECG10 or SK9139, may be found at
most local electronics parts dealers.
The Rules of the FCC (Federal Communications Commission) and your kit built
FM Stereo Transmitter.
An interim explanation of applicable FCC regulations supplied as a personal
assistance to FM10A builders, by Dan F. Onley (K4ZRA)
It is the policy of Ramsey Electronics, Inc., that knowing and observing the
lawful use of all kits is a first responsibility of our kit user-builders. We do not
endorse any unlawful use of any of our kits, and we do try to give you as much
common sense help about normal and lawful use as we can. Further, it is the
policy of Ramsey Electronics, Inc., to cooperate with all applicable federal
regulations in the design and marketing of our electronics kit products. Finally,
we urge all of our overseas customers to observe the regulations of their own
national telecommunications authorities.
In all instances, compliance with FCC rules in the operation of what the FCC
terms an "intentional radiator" is always the responsibility of the user of such an
"intentional radiator".
To order your copy of FCC rules part 15, call the US Government,
Superintendent of Documents, at 202-512-3238, or fax at 202-512-2250. To
order the correct document, ask for “CFR Title 17: Parts 1 to 19.” The cost is
$24.00, Master Card and Visa accepted.
In the United States, this is how the FCC regards your transmitter kit:
Licensed FM broadcast stations and their listeners have ALL the rights! Your
use of a device such as the FM10A kit MAY have some limited privileges in
locally-unused band space.
Unlicensed operation of small transmitting devices is discussed in "Part 15" of
the FCC Rules. These Rules are published in 100 "Parts," covering everything
imaginable concerning the topic of "Telecommunications." The six books
containing the FCC Rules are section 47 of the complete Code of Federal
Regulations, which you are likely to find in the Reference section of your Public
Library. If you have questions about the legal operation of your FM10A or any
other kit or home-built device which emits RF energy, it is your responsibility to
study the FCC regulations. It is best if YOU read (and consult with a lawyer if
you are in doubt) the rules and do not bother the understaffed and busy FCC
employees with questions that are clearly answered in the rules.
Here are the primary "dos and don'ts" picked from the current FCC Rules, as
of May, 1990. This is only a brief look at the rules and should not be
construed to be the absolute complete legal interpretation! It is up to you to
operate within the proper FCC rules and Ramsey Electronics, Inc. cannot be
held responsible for any violation thereof.
1. In the past, no "two-way communications" use of the 88-108 MHz FM
broadcast band was permitted. This prohibition does not appear in the
current edition of Part 15. Previous editions of Part 15 discussed "wireless
microphones" (such as Ramsey FM-1, FM-4, etc.), while the June 23, 1989,
revision eliminates this discussion in favor of more detail regarding computer
and TV peripherals and other modern electronic conveniences. However, it
is not immediately clear that the 1989 revision of the FCC Rules Part 15
necessarily "cancels" previous regulations. Laws and rules tend to remain
in force unless they are specifically repealed. Also, FCC Rule 15.37
discusses "Transitional Provisions for Compliance with the Rules," and
states in item (c): "There are no restrictions on the operation or marketing of
equipment complying with the regulations in effect prior to June 23, 1989."
2. It is the sole responsibility of the builder-user of any FM broadcast-band
device to research and fully avoid any and all interference to licensed FM
broadcast transmission and reception. This instruction manual gives you
practical advice on how to do a good job of finding a clear frequency, if one
is available.
3. For some frequency bands, the FCC sets 100 milliwatts (0.1 watt) as the
maximum permitted power output for unlicensed, home-built transmitting
devices, and that the combined length of your antenna and feedline (coaxial
cable or other) must not exceed 10 feet. The technical standards for 88-108
MHz are very different, primarily concerned with band width and RF field
4. FCC Rules do not differ for "stereo" or "monaural" transmissions.
5. Broadcasting on the grounds of a school (AM emissions only) is
specifically permitted and encouraged between 525 and 1705 KHz under
Part 15.221. Use our AM-1 AM radio broadcast kit for this use.
6. FCC Rule No. 15.239 specifically addresses operation in the 88-108
MHz FM broadcast band for which your FM10A transmitter kit is designed.
However, this Rule does not, by itself, tell you everything you need to know
about using a device of this kind. Therefore, we are noting a series of Part
15 regulations which should be observed:
a. The transmitter must NEVER be tuned to a frequency above 108
MHz, specifically the band 108-121.94 MHz, FCC Rule 15.205 lists this
band as restricted, due to potential interference with aircraft navigation
b. The "bandwidth" of your transmission is limited to 200 KHz, centered
on the actual operating frequency. Since 200 KHz is enough spectrum
space for several different FM stations, this is a "generous" limitation
designed to accommodate cruder FM devices. Properly built and
adjusted, the FM10A kit operates well within this limit. In fact, its signal
should sound no "wider" than any other FM station when listening on an
ordinary FM radio.
c. FCC Rule 15.215(a) says: "Unless otherwise stated, there are no
restrictions as to the types of operations permitted under these
sections." This general provision appears to leave you free to use your
FM stereo transmitter in a manner similar to operations of an FM
broadcasting station, or to use it for any other non-interfering, practical
d. FCC Rule 15.5: General conditions of operation: "(b) Operation...is
subject to the conditions that no harmful interference is caused and that
interference must be accepted that may be caused by the operation of
an authorized radio station, by another intentional or unintentional
radiator, by industrial, scientific and medical equipment, or by an
incidental radiator. (c) The operator of a radio frequency device shall be
required to cease operating the device upon notification by a
Commission representative that the device is causing harmful
e. The most specific FCC regulation of 88-108 MHz FM Broadcast band
unlicensed operation is that the "field strength" of the signal must not
exceed 250 microvolts/meter at a distance of 3 meters from the
transmitter (FCC rule 15.239). If you have any concern about this
emission limit, have your device checked by a technician with accurate
measuring equipment. Remember that the "field strength" of a signal is
determined as much by the antenna as by the RF output of the
transmitter itself.
A "microvolt" is one-millionth of one volt and designated "µV" in the
following explanations.
The new FCC Part 15 Rules specify a maximum "Field Strength" of your
transmitted signal. Since it is unlikely that you have the equipment to carry
out accurate field strength measurements in microvolts, it is useful to
understand at least the theory of field strength so that you can understand
both what you can expect from such transmitters, and what limits the FCC
Previous limits on nonlicensed FM-broadcast band devices were defined
as a maximum field strength of 40µV per meter measured at a distance of 15
meters. The June 1989 revised rule specifies a maximum of 250 µV per
meter, but measured at 3 meters from your antenna. Both limitations are the
same in practice. "250µV per meter" means that an accurate field-strength
meter with a 1-meter antenna may indicate a maximum signal field strength
of 250µV (In contrast, non-licensed operation from 26.96 to 27.28 MHz is
limited to a field strength of 10,000 µV per meter at 3 meters).
In all cases, the field strength of a signal decreases in direct proportion to
the distance away from the antenna. Power decreases by the square of
distance: for every doubling in distance, the signal power is quartered, but
the field strength voltage is only halved. Using this theory, we can construct
a simple chart to show the maximum permitted performance of a nonlicensed FM band transmitter. The theoretical figures assume a simple 1
meter receiving antenna in all cases and do not take into consideration that
reception can be greatly enhanced with larger, multi-element antennas and
preamplifiers. In the following chart, the field strength (theoretical minimum)
gets even stronger as you move from the edge of these circular boundaries
toward the antenna:
This "exercise in meters and microvolts" demonstrates that the FCC clearly
intends to limit the theoretical range of non-licensed devices operating in this
band. It also shows the potential for causing interference at a home down
the street from you. But it also shows that you can legally put out quite a
good signal over wider areas than you might have imagined.
For other kinds of radio services, the FCC restricts such factors as
transmitter power or antenna height, which cannot really limit the possible
"range" of a transmission under good conditions. By restricting the maximum
field strength at a specific distance from your antenna, the FCC clearly plans
for your signal to "die out" at a specific distance from your antenna, no matter
what kind of transmitter power or extra-gain antenna you are using. On the
other hand, the FCC standards do make it legal and possible for you to
314 FT
1256 FT
4800 FT
19113 FT
28.6 ACRES
11.4 ACRES
1830 ACRES
broadcast on a school campus, campground or local neighborhood, as long
as you do not cause interference to broadcast reception.
“Why talk about acres"?
There are three reasons to translate our look at "field strength" into "acres".
(1) The first one is easy: the numbers would get too cumbersome if we
discussed your possible signal coverage in terms of square feet or
square meters.
(2) It's very easy to see that your signal can easily and legally serve a
school campus or wilderness campground.
(3) And, if we remember that typical urban single-family home sites run
from 1/4 to 1/2 acre on the average, it should become extremely clear
that your obligation to avoid interfering with broadcast reception can
easily involve hundreds of homes, before adding apartments!
In fact, the most significant distance in the above chart is the 1.9 µV signal
strength permissible at 1260 feet (about 1/4 mile), covering a circular area of
about 114 acres. A quick glance at stereo FM receiver specifications shows
typical sensitivity of 1.7 µV before considering high-gain antennas or
preamplifiers. Your non-licensed signal can provide serious competition to a
public broadcast station fifty miles away, a station which someone in your
neighborhood may have set up a special antenna to enjoy.
Calibrated "field strength meters" such as described in the ARRL Radio
Amateur's Handbook can detect signals down to about 100 microvolts. To
measure RF field strength below such a level, professional or laboratory
equipment and sensitive receivers are required. A "sensitive" receiver
responds to a signal of 1 or even .5 microvolt "delivered" to the receiver input
by antenna. If the antenna is not good, the receiver cannot respond to the
presence of fractions of a microvolt of RF energy.
The present edition of Part 15 of the FCC rules does not provide detailed
guidance on ALL aspects of using a low-power transmitter such as the
FM10A. The main point is that you may not cause any interference
whatsoever to licensed broadcast services and that you must be willing to
put up with any interference that you may experience.
In addition to operations not requiring authorization, you also have the
option of writing a clear and polite letter to the FCC Engineer-in-Charge of
your local district, describing your intended operation. Mention the operating
frequency and planned hours of operation. This could be a good step to take
if your project is on behalf of a school, Scout or community group.
If you become further fascinated with the service rendered by low-power
broadcasting, other FCC regulations explain how to apply for a license or
other authorization which may permit you to upgrade your FM10A or other
equipment to accomplish any objective which the FCC sees to be in the
public interest and not interfering with other authorized uses of the radio
Lawful use suggestions for the FM10A
1. Build and adjust this kit strictly according to the published
2. Use the whip antenna supplied with the Ramsey case set, CFM.
3. Do not modify your kit in any way.
4. Check your intended operating frequency very carefully, as clearly
explained in this instruction manual, to ensure you will not cause
interference to reception of licensed broadcasting.
5. If you receive ANY complaint about your transmissions interfering
with broadcast reception, stop or change your operation
6. If you are contacted by the FCC regarding use of this device,
cooperate fully and promptly.
7. Do your own homework and research to understand and comply
with present and future FCC rulings concerning devices of this kind.
8. Do not use made-up "station call signs" to identify your
transmissions. Only the FCC has the authority to issue such callsigns.
Use some other way to identify your transmitting activity, such as
"This is Stereo 90.5, Seabreeze School Student Music Radio," and so
9. Identify the location and purpose of your transmissions from time to
time. This is common courtesy toward other persons who may hear
your signal. The FCC is toughest about clandestine transmission
which cost time and money to track down.
10. Do not assume that the mere fact that you purchased this kit gives
you any specific right to use it for any purpose beyond generating a
low-level RF signal which is barely detectable beyond the perimeter of
your personal dwelling space.
Finally, the FCC Rules call for the posting of printed notices on devices
intended for non-licensed operation under Part 15 Rules. You will find such
notices written up for the front or back of the instruction manual for nearly
any computer or video accessory that you have seen in recent months.
Consult the Part 15 Rules for the exact wording of such notices. Following is
a text for such a notice which responds to FCC rule making intentions:
The radio-frequency "intentional radiator" device which may be
constructed from kit parts supplied by us is intended and designed by
Ramsey Electronics, Inc. to conform to applicable provisions of Part 15 of
FCC Rules. The individual kit-builder and all users of this device assume
responsibility for lawful uses conforming to FCC Part 15 Rules. Operation is
subject to the following two conditions:
[1] This device may not cause harmful interference, and
[2] this device must accept any interference received, including interference
that may cause undesired operation.
Final comment
A well-informed person will see today's FCC Rules to be evolving and
progressively less-restrictive. Even though today's technology is far more
complex than what was possible at the time of the Communications Act of
1934, the FCC rules are becoming more relaxed, giving radio experimenters
more and more opportunities to explore many frequency bands, using many
communications modes, with no need for a formal license of any kind. A
thorough study of Part 15 of the FCC Rules, which is completely beyond the
purpose of this kit manual, will show you many legal uses of radio
transmitting devices which do not require licensing, either amateur or
To provide more personal and club radio-learning opportunities, and to cut
down on administrative costs, today's FCC permits far more non-licensed
activity than at any time in previous history. On the other hand, today's FCC
enforcement actions get bigger fines and real prison terms for scofflaws!
From CB (now 3 bands of it, for varying applications) to easy entry-level
Amateur Radio with long-term licensing, to numerous unlicensed Part 15
operations, the FCC is beginning to look out for the interest and good plans
and intentions of private citizens and school-community groups as never
before in radio communications history. Learn the rules...observe them...and
have fun in radio!
If you enjoyed this Ramsey kit, there're plenty more to choose from in our
catalog - write or call today!
The Ramsey Kit Warranty
Please read carefully BEFORE calling or writing in about your kit. Most
problems can be solved without contacting the factory.
Notice that this is not a "fine print" warranty. We want you to understand your rights and ours too! All
Ramsey kits will work if assembled properly. The very fact that your kit includes this new manual is
your assurance that a team of knowledgeable people have field-tested several "copies" of this kit
straight from the Ramsey Inventory. If you need help, please read through your manual carefully, all
information required to properly build and test your kit is contained within the pages!
1. DEFECTIVE PARTS: It's always easy to blame a part for a problem in your kit, however, customer
satisfaction is our goal, so in the event that you do have a problem, take note of the following. Before
you conclude that a part may be bad, thoroughly check your work. Today's semiconductors and
passive components have reached incredibly high reliability levels, and its sad to say that our human
construction skills have not! But on rare occasions a sour component can slip through. All our kit parts
carry the Ramsey Electronics Warranty that they are free from defects for a full ninety (90) days from
the date of purchase. Defective parts will be replaced promptly at our expense. If you suspect any part
to be defective, please mail it to our factory for testing and replacement. Please send only the
defective part(s), not the entire kit. The part(s) MUST be returned to us in suitable condition for testing.
Please be aware that testing can usually determine if the part was truly defective or damaged by
assembly or usage. Don't be afraid of telling us that you 'blew-it', we're all human and in most cases,
replacement parts are very reasonably priced.
2. MISSING PARTS: Before assuming a part value is incorrect, check the parts listing carefully to see
if it is a critical value such as a specific coil or IC, or whether a RANGE of values is suitable (such as
"100 to 500 uF"). Often times, common sense will solve a mysterious missing part problem. If you're
missing five 10K ohm resistors and received five extra 1K resistors, you can pretty much be assured
that the '1K ohm' resistors are actually the 'missing' 10 K parts ("Hum-m-m, I guess the 'red' band
really does look orange!") Ramsey Electronics project kits are packed with pride in the USA. If you
believe we packed an incorrect part or omitted a part clearly indicated in your assembly manual as
supplied with the basic kit by Ramsey, please write or call us with information on the part you need and
proof of kit purchase.
To qualify for Ramsey Electronics factory repair, kits MUST:
1. NOT be assembled with acid core solder or flux.
2. NOT be modified in any manner.
3. BE returned in fully-assembled form, not partially assembled.
4. BE accompanied by the proper repair fee. No repair will be undertaken until we have received the
MINIMUM repair fee (1/2 hour labor) of $18.00, or authorization to charge it to your credit card
5. INCLUDE a description of the problem and legible return address. DO NOT send a separate letter;
include all correspondence with the unit. Please do not include your own hardware such as
nonRamsey cabinets, knobs, cables, external battery packs and the like. Ramsey Electronics, Inc.,
reserves the right to refuse repair on ANY item in which we find excessive problems or damage due
to construction methods. To assist customers in such situations, Ramsey Electronics, Inc., reserves
the right to solve their needs on a case-by-case basis.
The repair is $36.00 per hour, regardless of the cost of the kit. Please understand that our technicians
are not volunteers and that set-up, testing, diagnosis, repair and repacking and paperwork can take
nearly an hour of paid employee time on even a simple kit. Of course, if we find that a part was
defective in manufacture, there will be no charge to repair your kit (But please realize that our
technicians know the difference between a defective part and parts burned out or damaged through
improper use or assembly).
4. REFUNDS: You are given ten (10) days to examine our products. If you are not satisfied, you may
return your unassembled kit with all the parts and instructions and proof of purchase to the factory for a
full refund. The return package should be packed securely. Insurance is recommended. Please do not
cause needless delays, read all information carefully.
Quick Reference Page Guide
Introduction ...................................... 4
Circuit description ............................ 5
Schematic diagram .......................... 5
Parts list ........................................... 6
Parts layout board ............................ 7
Assembly instructions ...................... 8
Adjusting your FM10A...................... 14
Troubleshooting guide ..................... 18
Appendix A: FCC rules and info....... 19
Appendix B: Field strength ............... 22
Warranty .......................................... 27
• Soldering Iron (Radio Shack #RS64-2072)
• Thin Rosin Core Solder (RS64-025)
• Needle Nose Pliers (RS64-1844)
• Small Diagonal Cutters (RS64-1845)
• <OR> Complete Soldering Tool Set
• Soldering Iron Holder/Cleaner (RS64-2078)
• Holder for PC Board/Parts (RS64-2094)
• Desoldering Braid (RS-2090)
Manual Price Only: $5.00
Ramsey Publication No. MFM10A
Assembly and Instruction manual for:
793 Canning Parkway
Victor, New York 14564
(716) 924-4560
(716) 924-4555
Beginner .............. 3.5 hrs
Intermediate ........ 2 hrs
Advanced ............. 1.5 hrs
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