IC746PRO vs. IC756PROII — A Contester`s Comparison

IC746PRO vs. IC756PROII — A Contester`s Comparison
IC746PRO vs. IC756PROII
— A Contester’s Comparison
This is a companion article to the one
I wrote for the May/June 2002 issue of
NCJ entitled A Contester’s View of the
IC-756PROII. Since that article was written, I have put considerable mileage on
a pair of ’756PROII’s, and ICOM has introduced the IC-746PRO.
What I have provided in this article is
a qualitative evaluation of my overall
experience with the ’756PROII and a
comparison of the ’756PROII to the
’746PRO. I do not generally operate
data, VHF, RTTY, AM or FM, so I have
not included any evaluation of these
modes.
QST published detailed product reviews by Rick Lindquist, N1RL, of the
IC-756PROII and IC-746PRO in February and May 2002, respectively. Each of
these articles provided excellent technical reviews of the radios, including
performance characteristics, laboratory
measurements and comparisons to previous versions of each model. The May
2002 article also provided a “side by
side” comparison of the two radios. A
detailed study of the ’746PRO receiver’s
performance numbers described in that
article will lead you to conclude that the
receiver is on balance with that of the
’756PROII — a conclusion that I can
second after doing on the air comparisons of both radios. I recommend a review of these two articles, which are
available to members on the ARRL Web
site.
My two IC-756PROIIs have been subjected to heavy use in contests, routine
daily operation and three tr ips to
Dominica (J7) where multiple operators
used them. With the exception of one
failure caused by lighting and another
from operation with a faulty amp, these
’756PROII’s have performed flawlessly.
A new IC-746PRO used in the August
NAQP SSB contest and during two
weeks of daily operation (rag chewing
and chasing DX) was the basis for comparing the performance of the ’746PRO
to that of the ’756PROII. I found the sensitivity and selectivity of the ’746PRO’s
receiver, as well as its dynamic range
— the ability to copy a weak signal in
the midst of adjacent strong QRM — to
be excellent. On the transmit side, I
found the ’746PRO to be equal to the
’756PROII. I have not had a chance to
use a ’746PRO in a CW contest, but I
have no doubt that its basic performance
would score on a par with my
’756PROIIs.
24 November/December 2003 NCJ
George I. Wagner K5KG
k5kg@arrl.net
Similar Features of the Two Radios
Many features of the ’746PRO and the
’756PROII are identical and I have nothing further to add about their functionality. These features include: MIC,
PHONES, SPEAKER, NUMBER KEYPAD, RIT & ?TX, TWIN PBT, NB,
MEMORIES and XFC.
Other apparently similar features of
both radios are important to discuss,
however. These are features of the radios that I feel are especially important
to understand, either because I have
learned something about them through
experience, or because they are subtle
and I believe need to be highlighted.
The author standing over the
’746PRO and ’756PROII
Close-up of ’746PRO and ’756PROII
Basic Radio Functions
When it comes to the basic receive
and transmit capabilities of the two radios, they are essentially equal in terms
of functionality and performance. Both
have 100 W output transmitters. They
both use the same DSP engine. Both
cover 160 through 6 meters, although a
big differentiator is that the ’746PRO
also includes 2 meters (with the full 100
W output on 2 meters!). Both offer general coverage receivers covering 30 kHz
through 60 MHz. The ’746PRO also has
additional receiver coverage from 108
MHz to 174 MHz. There is approximately
a $1,000 difference in the street price
of the two radios, with the ’756PROII being the more expensive.
DSP Functionality
DSP filter shape and filter bandwidth
controls on both radios appear similar.
On both the ’746PRO and the
’756PROII, the DSP filter shape can be
set to either soft or sharp and filter bandwidth (BANDWIDTH) is adjustable from
50 Hz to 3.6 kHz. On the ’746PRO, adjusting both filter shape and bandwidth
is easily done with a one second push
of the FILTER button which brings up
the filter adjustment display. Accessing
the same function on the ’756PROII is
more difficult. On the ’756PROII, a one
second push of the FILTER button only
brings up a filter bandwidth adjustment
display (no shape adjustment). Changing filter shape requires four pushes of
the EXIT/SET button to get to the DSP
filter set display. I definitely liked the
ability on the ’746PRO to set BANDWIDTH and SHAPE from the same display.
DSP noise reduction (NR) is an outstanding feature of both radios. The level
of NR is fully adjustable with the front
panel control. At times, during marginal
band conditions — weak signals buried
in QRN — I found that introducing NR,
just to the level where it begins to take
effect, provides the best results for pulling weak signals out of the noise. I found
no difference in NR functionality between the ’746PRO and the ’756PROII.
Frequency Tuning
Both radios are very flexible in selecting rates of tuning. Frequency is displayed to the nearest 10 Hz as the default. A one second push of the TS button turns on an additional digit, thereby
providing frequency resolution to one
Hz. On CW, pushing the 1/4ON button
provides band spread to an amazing
125 Hz per dial revolution on the
’756PROII (150 Hz on the ’746PRO)! A
momentary push of TS turns on quick
tuning. This function allows the operating frequency to be changed in selectable steps from 100 Hz to 25 kHz for
“quick tuning” from one end of a band
to the other. Activating Main Dial Auto
TS will cause quick tune to kick in automatically when rapidly turning the
main dial.
Memo Pads
Both radios have a memo pad function which stores frequency and operating mode for easy recall. A push of
the MP-W button stores the current frequency and operation mode. Change
frequency or operating mode and push
MP-W again, and the new frequency
and operating mode will be stored – and
so on, up to five or ten (user selectable)
levels of storage. A push of MP-R recalls the stored frequencies and operating modes, last in first out (LIFO). This
feature is especially useful when chasing DX or searching and pouncing in a
contest, and is somewhat analogous to
the search and pounce memory function in WriteLog.
Split Operation
The ’746PRO and the ’756PROII have
similar split frequency features, including “quick split”. With quick split activated
(in the SET menu), a one second push
of the SPLIT button sets the frequency
of VFO B to that of VFO A. F-INP is then
used to input a kHz split (e.g., 1 kHz or
2 kHz) on the number keypad. When
SPLIT is pushed again, VFO B is then
changed to the split transmit frequency.
CW Operating
Semi break-in works equally well on
both radios. Full break-in, however,
sounds slightly “choppy” at higher CW
speeds; this is tr ue with both the
’746PRO and the ’756PROII. The only
way I have discovered to cure this problem is to use an external Logikey keyer
(www.idiompress.com). The Logikey
keyer has built in adjustable “keying
compensation” that increases keying ontime and decreases keying off-time by
a few milliseconds to correct the full
break-in distortion. Setting the keying
compensation anywhere from 6 to 10
milliseconds cures the problem and produces beautiful sounding, high speed
CW using full break-in.
In both the ’746PRO and the
’756PROII, a keyer rise time adjustment
sets the time it takes for output power to
raise to the set transmit power level. It
is adjustable from 2 to 8 milliseconds. I
received complaints of key clicks during
my early days with the 756PROII, and
discovered that a rise time of 2ms was
causing the problem. I adjusted rise time
to 6ms and received no further complaints. Like the ’756PROII, the ’746PRO
also produces key clicks when rise time
is too short. Setting the ’746Pro’s rise
time to 6 or 8ms will reduce the clicks to
a tolerable level.
John Seney, WD1V, did an excellent
analysis of ’756PROII rise times using
a digital oscilloscope to view the keyed
waveforms at various settings of rise
time. This analysis is available at
www.qsl.net/wd1v/756cw.html. John
explains that “too fast a rise time can
cause key clicks that are essentially
analog distortions of the CW waveform
that contain out of band products that
produce noise (clicks). If the keying circuit lets the transmitter go from zero
power to full power too rapidly the
transmitter’s output becomes distorted.”
Both the ’746PRO and the ’756PROII
have four memories for storing CW messages to be transmitted. A push of one
of the four MEMORY KEYER buttons
(M1 through M4) transmits the respective CW message. A momentary push
of the same memory button or a tap of
the paddle stops the message from being sent. Messages are transmitted at a
speed controlled by the internal keyer’s
KEY SPEED adjustment on the front
panel.
When sending stored CW messages
on the ’746PRO, Menu M1-KEY-SND
displays scrolling characters of the CW
message as it is being sent — a clever
feature that is useful for code practice.
There is a repeat timer on both radios
that allows you to automatically repeat
any of the four CW messages at intervals from 1 to 60 seconds. Holding the
MEMORY KEYER button (M1 – M4 )
for one second activates the repeat
timer.
A CW paddle connected to the ELECKEY jack on the front panel of the radio
keys the internal keyer. The KEY jack
on the rear panel bypasses the internal
keyer and must be used with an outboard keyer or for computer generated
keying. In my case, I use both a Logikey
K-3 keyer and computer generated keying, so I use a stereo Y connector for
paralleling the two 1/4 inch plugs into
the rear KEY jack.
Voice Operation
Since different microphones have different audio characteristics, it is a good
idea to do some on-the-air testing with
a friend to determine the TX bandwidth,
TX treble and TX bass that sounds best
for your set up. The monitor function will
also allow you to listen to your TX audio
while you make the adjustments. There
are also RX treble and RX bass adjustments that should be set to your preferences.
Accessories and Connections
The I-MATE is an accessory for the
’746PRO and the ’756PROII, developed
and sold by The BetterRF Company
(www.betterRF.com). Its purpose is to
provide the external keypad function to
trigger the sending of voice and CW
messages. Using the I-MATE with the
’756PROII allows the spectrum scope to
be visible while having access to the
memory send function. The I-MATE
works equally well with both radios.
However, since the ’746PRO does not
have a recorder for storing voice messages to be transmitted, the I-MATE will
only trigger CW messages with that radio. The repeat timer works well with the
I-MATE. Holding down any one of the IMATE’s MEMORIES buttons for one
second activates the repeat timer for that
NCJ November/December 2003 25
message.
I use WriteLog for contests and my
everyday logging. Since WriteLog does
not have a “Rig Type” selection for either the IC-756PROII or IC-746PRO, I
used Rig Type “ICOM-756PRO” on
WriteLog’s setup menu to control both
radios. In each radio, the CI-V Baud Rate
is set to 9600 and the CI-V Address to
“5Ch”.
The specifications for the SEND relay contacts are 16 V dc at 500ma. An
early version of the IC-756PROII manual
indicated 16 V dc at 2 A, but this was
wrong and was corrected in a later version of the manual. If you are going to
use the transceiver’s SEND jack for
keying a linear amplifier, be sure that the
amp does not exceed these specifications, else the radio’s internal reed relay may be damaged. If the amp’s keying relay requires a higher current than
500ma, or exceeds 16 V dc, you can use
pin 7 (+13.8 V dc) and pin 3 (TX Ground)
of either ACC(1) or ACC(2) to key an
external 12 V dc relay which, in turn, can
key an amplifier.
These are nominal 12 V dc radios, and
any good, electrically clean, 13.8 V dc
supply capable of delivering at least 23 A
should handle them just fine. The ICOM
PS-125 power supply is popular because
it is currently being offered at no additional
cost by some dealers with the purchase
of a new ’746PRO or ’756PROII. The
ICOM PS-125 is a physically compact unit
that powers either radio quite nicely. Note,
however, that it has a 16 inch 12 V dc
power cable that makes it necessary to
locate the power supply adjacent to the
radio. A slight amount of fan noise is
noticeable. Curiously, the fan cycles on
and off even with the 12 V dc cable unplugged from the radio. In my shack, I
power the radios with an Astron power
supply.
The label marking the various connections on the rear panel is quite small and
difficult to read. I used a Brother P-Touch
label maker to make labels for each rear
panel jack and connector. As I pointed
out in my previous article, I keep a flashlight handy!
Features That Differ Between the
Two Radios
Displays
Clearly a major difference between
the ’746PRO and the ’756PROII is the
LCD display. The basic display functions
(frequency readout, function switch
menus, memor y channels, set up
modes, etc.) are quite similar, but their
looks are totally different, with the primar y difference being color. The
’746PRO has a bright white screen with
crisp blue lettering that I find very pleasing to use. It displays all of the many
26 November/December 2003 NCJ
pieces of information I need as an operator conveniently and legibly. The color
display on the ’756PROII, however, is
magnificent — with the colors adding a
dimension that makes it exceptionally
easy to recognize the wealth of information that is displayed.
There is no comparison between the
spectrum scope on the ’756PROII and
the band scope on the ’746PRO. The
’756PROII’s spectrum scope provides
an active, real time display of the relative strengths of signals around a center frequency. The span can be set to +/
- 12.5 kHz, +/-25 kHz, +/-50 kHz and +/
-100 kHz. I have become so accustomed
to this spectrum display, especially during heavy contest conditions, that to do
without it at this point in my life is unthinkable. The scope is an invaluable tool
for “finding holes” and moving away from
offending QRM in a crowded band and
for finding signals on a “dead” band.
The ’746PRO’s band scope allows —
in a limited way — the ability to check
signal conditions around a center frequency. The scope indicates the relative
strength of signals and their locations
with respect to the center frequency. The
sweep width is adjustable in steps from
500 Hz to 25 kHz. Unlike the ’756PROII’s
spectrum scope, the signal display is not
active in real time. Each time you want
to see a profile of the signals above and
below the center frequency, you must
push the F1 button to activate a scan to
refresh the display. The scan lasts only
a moment but, during that time, the audio is muted. You can turn on an active
display of the signals by holding down
the F1 button for one second. You can
even tune up and down the band, “looking” for signals while the active scan is
underway. However, once again, the
audio is muted, thus making the “active”
scan virtually useless. My personal conclusion about the ’746PRO’s band scope
is that it is a very marginal feature on
the radio, one that certainly would not
be useful in a contest. Furthermore, I
find the loss of audio while scanning to
be unacceptable.
The many menu selections on both
the ’746PRO and the ’756PROII will lead
you into the inner depths of the radios,
not unlike exploring an Egyptian tomb. I
am constantly amazed at the functionality that brilliant engineers design into
modern day radios and these ICOM
models are an embodiment of that talent. Virtually anything an operator would
wish to set, adjust, manipulate, influence, control, regulate, alter, fiddle with,
bend, amend or modify can be found
somewhere in a menu! The trick is knowing how and where to set, adjust, manipulate, etc., etc…you get the point. It
is difficult to say if the menu layout in
the ’756PROII is superior to that of the
’746PRO. They are both complex, and
each requires a thorough study of their
manuals to get a complete understanding. I do, however, personally prefer the
menus of the ’756PROII since many
selections are presented in a convenient
table on the color LCD screen. I will
make one last point about the many features buried in the menus. That is, in
researching this article, I have discovered features in the ’756PROII that I had
no idea were there, and I have been
actively using this radio for two years!
The ’756PROII has a dual watch feature and an audio balance (BAL) control that allows for monitoring of VFO B
while listening on VFO A. The ’746PRO
does not have dual watch capability.
The ’756PROII has four memories for
storing voice messages to be transmitted. A push of one of the four MEMORY
KEYER buttons (T1 through T4 ) transmits the respective voice message. A
momentary push of the same memory
button stops the message. As discussed
above, the I-MATE can be used to trigger the sending of the voice memories
in the ’756PROII. Note - the repeat timer
only functions on CW and, therefore,
does not work with the voice memory
keyer on the ’756PROII.
Antenna Options
Both the ’746PRO and the ’756PROII
have two antenna ports for HF thorough
6 meters. Antenna Switch selection can
be set to OFF, MANUAL or AUTO in
the SET Menu. In the OFF position,
antenna port 1 is “locked in” on each
band, and cannot be changed from band
to band. In the MANUAL position, selection of antenna port 1 or 2 must be
done manually when switching from one
band to another. In the AUTO position,
selection of antenna port 1 or 2, as preset by the operator, is done automatically on each band.
The ’746PRO has a separate antenna
port for 2 meters.
The ’756PROII has a rear panel RCA
jack for connecting a separate receiving antenna. A one second push of the
ANT button selects the receiving antenna and 1/R or 2/R is displayed as the
antenna. A separate receiving antenna
port is not available on the ’746PRO, a
severe limitation for serious contesters
and low band DX’ers.
As protection from external RF voltages, I use an ICE Model 196 RF Limiter/Arrestor at the input to the
’756PROII from my receiving antenna.
Dimensions
The ’756PROII is some 34 cubic
inches larger in volume and 1 pound 6
ounces heavier than the ’746PRO, which
is a consideration when packing for a
DXpedition. The ’756PROII is approxi-
mately 2 inches wider, 1¼ inch less deep
and of equal height to the ’746PRO.
Conclusion
The ’746PRO and the ’756PROII are
both excellent radios and alike in many
ways. The 756PROII has numerous features beyond those of the ’746PRO. The
more significant ones, in my opinion,
include: LCD color display, real time
band scope, multi-level attenuator, analog meter, clock, dual watch, TX voice
memories, digital voice recorder and
separate RX antenna port. On the other
hand, the ’746PRO has a 100 W, 2-meter
capability that makes it an attractive “all
in one” package.
In choosing one radio over the other
it really comes down to how the operator values the extra features on the
’756PROII relative to the $1,000 difference in their cost AND his or her operating preferences.
For the casual operator who occasionally works a contest, likes to chase DX
and spends much of his or her time rag
chewing, the ’746PRO offers excellent
value as a full function HF, 6 and 2 meter
Additional differences are summarized below.
Feature
Analog meter
Clock & timer
Digital voice recorder
Voice message recorder for TX
CW message recorder for TX
Attenuator (ATT)
Preamp/ATT
Preamp 1
Preamp 2
Preamp – 2 meters
Tx filter width – NAR
Tx filter width – MID
Tx filter width – WIDE
ACC(2) on rear panel
Data Socket on rear panel
IC-756PROII
Yes – multi function
Yes
8 memory channels 15 sec. Ea
4 each for TX and RX,
4 memory channels, 90 sec. total
4 memory channels,
55 char. max each
6, 12 or 18 db
Yes, separate buttons
10db for all HF bands
16db for 24 MHz and up
N/A
2.0 kHz
2.6 kHz
2.9kHz
Pin 6 activates on XVERT I/O
None
IC-746PRO
None
None
None
None
4 memory channels
50 char. max each
20 db
Yes single button
1.8 to 21 MHz*
24 to 50 MHz*
108 to 174 MHz
2.2 kHz
2.4 kHz
2.8 kHz
Pin 6 to gnd on 2m TX
TNC jack
*Gain unspecified
radio that can be bought new for under
$1400. Price, weight and volume also
make the ’746PRO a serious contender
as a DXpedition radio. For the active
contester and serious DX’er, however,
the bottom line is that the LCD color display, real time band scope, multi-level
attenuator, dual watch and separate RX
antenna port most likely justify the additional cost of the IC-756PROII.
NCJ November/December 2003 27
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