Icom IC-756 PRO III Page


Thanks to Ray Novak N9JA with Icom America for allowing me to evaluate the new Icom IC-756PROIII.  Ray is heavily involved in Icom’s award sponsorship for the NAQP RTTY contests held in February and July each year.  After several consecutive winning efforts in the NAQP RTTY event, Ray asked me what kind of radios I used.  When I told him “Kenwood”, he asked “What do we have to do to get you to run Icom radios?”.  I said “Just send them to me”.  And he did – two new PRO III’s which arrived on December 21, 2004.

I received the radios at my office.  Since it was the week of Christmas, it was slow enough to allow me to unpack one and connect it to the Cushcraft A3S tribander I have on a 50′ tower at work.  In a couple of hours, by going through the manual and testing the different functions of the radio, I felt comfortable with it right away.  Everything was quite well laid out, the manual was informative and operation of the radio was quite easy.  Since my office is located in an industrial park, there is a lot of noise.  The first thing I noticed was how well the noise blanker and noise reduction functions worked.

With the VU4 DXpedition underway, I was anxious to get the radios home and in a more quiet environment to try to work them on CW.  I had already made a questionable SSB QSO and a good PSK31 contact, but a solid SSB and CW contact still eluded me.  When I got home, I disconnected all the cables going to my IC-775DSP and replaced it with one of the PRO III’s in a matter of minutes.  All the cables were interchangeable.  I had to route DC power to the PRO III since the ‘775 has it’s own internal power supply.  I then set the ALC on the IC-PW1 amplifier and I was ready to go just after 0001Z on the 22nd.  At 0217Z, I made my first contact with the radio.  It was a good contact with VU4RBI on 14191 KHz!  In the following days, I listened for the VU4 stations on CW for many hours without making a contact before the earthquake and tsunami hit Andaman and Nicobar.

Not being much of an experienced SSB operator, it was hard to tell the advantages of using the PRO III on that mode, but I can tell you it was the first time I actually heard VU4RBI clearly in over two weeks of listening to her.  I have to think the radio had something to do with it.

Finally on Christmas eve, I replaced my remaining TS-870 with the 2nd PRO III.  The PRO III is slightly wider than the TS-870.  It did not quite fit in the slot under the shelf of the operating desk so I had to remove the handle.  The PRO III’s were now side-by-side and they looked really cool so I took the picture shown above.

In the following days leading up to the ARRL RTTY Roundup, I spent a lot of time with the radios.  I was beginning to like them – a lot.  The spectrum display was nice but it didn’t seem much of an advantage in everyday DX work, but I was imagining how they would come in handy in a RTTY contest.  Since RTTY signals are basically solid carriers, I was thinking the spectrum analyzer would help tremendously on bands with low activity, like 10 meters might be in the contest.  I always start the Roundup on 10 and 15 meters.  With the spectrum analyzer, I would be able to spot new signals on the band – or at least I think I would.

The ARRL Roundup would be the perfect event to truly test these radios in an SO2R environment on RTTY.  I’m glad I was able to receive the radios early enough to get familiar with them before the Roundup.  The Roundup is a special contest for me.  It’s my favorite and the one I put the most effort into.

On the weekend before the contest, the PRO III proved invaluable in a way I could never have imagined.  While setting up the 2nd radio, I just happened to be looking at the spectrum display on Radio A on 15 meters when I turned on a DXP38 connected to Radio B and saw this area of noise immediately move on the display.  This caught my eye and curiosity.  There was this “blob” of noise on the high side of the 15 meter RTTY band.  When I turned anything on that was connected to the power supply feeding Radio B, the “blob” of noise would shift to the low side of the 15 meter RTTY band.  I immediately knew what was happening.  The power supply feeding the B radio was causing noise!  When I unplugged the supply (it’s always left on), I noticed the noise on 15 meters went completely away.  I checked the other bands and the most significant change was 17 meters.  I had always had such a high level of noise across 17 meters.  It was now completely gone.  This was a major improvement to my station.  I never suspected that power supply was generating noise.

The 2005 ARRL RTTY Roundup

The Roundup would be the first real test for the PRO III’s.  I was a little nervous about going into a major contest with new radios.  But I learned enough beforehand that during the contest I had absolutely no problems with them.

Now that the contest is over, I can say the PRO III is probably the best RTTY contest radio I’ve ever used to date.  I say “probably” because I only have 24 hours of contesting under my belt with them.  I still like my Kenwood TS-870’s and feel they are great RTTY contesting radios, but the PRO III gave me some things that give it an edge over the ‘870.

IF Filtering

The first thing I noticed about the PRO III was the different available IF filter settings.  There is the “regular” filter which can be used in the RTTY mode and then there is the “RTTY” filter.  And they are definitely different.  Without knowing any details of how the filters are set inside the radio (and the operating manual doesn’t give any details), I can tell you the “RTTY” filter is simply wonderful and works much better than the standard filter in a couple of ways.  The standard filter does not appear to be true in bandwidth as compared to the “RTTY” filter.  When looking at the FFT display in the MMTTY RTTY Control Panel set at 500 hz, you can plainly see the difference between the two filters.


Figure A shows the MMTTY audio FFT display with the standard 250 Hz IF filter active in the PRO III.  Figure B shows the same display with the 250 Hz IF RTTY filter turned on.  For these examples I had the receiver audio turned up higher than normal and was looking at noise.

The point I’m trying to make is that the RTTY filter is much sharper than the standard filter and works extremely well.  But the RTTY filter showed another property which surprised me.  When transmitting in the 80 meter RTTY sub-band, I can hear “hash” interference on 40 meters on the other radio due to my antennas being only a few feet apart (and using Dunestar 600 band filters on each radio).  Although this interference is very low, it’s enough to to prevent copying weak signals on 40.  With the “RTTY” filter activated and set to 250 Hz, this hash is greatly reduced by several db as shown on the radio’s spectrum scope and heard in the headphones.  So this radio has a great RTTY filter.  And it’s nice to be able to turn this filter on and off with a simple push of a button and to be able to change the bandwidth on the fly.

Some people don’t like a 250 Hz filter and say it’s too narrow.  I disagree.  I tried the 300 and 350 Hz bandwidth settings of the RTTY filter and found the 250 Hz filter worked the best for contesting.

Spectrum Scope

One word describes the spectrum display on the PRO III – awesome!    Icom calls it the spectrum scope.  I call it a big advantage in contesting and many PRO users already know this.  When I first got the radios I turned off the scope because I didn’t like it (noticed it is turned off in the picture at the top of this page).  I couldn’t think of any uses for it.  But I ran it for the Roundup most of the time.  I have to tell you that it can be distracting.  I want to be concentrating on what’s on my two computer screens and not the screens on my radio.  But when I realized the value of the spectrum scope, I was hooked.

The first thing I realized was that I could check a band for signals nearly instantly without tuning across the band.  I did this in the Roundup on 10 meters several times.  If I went to 10 meters and didn’t see any signals on the scope, I simply went back to the band I was on.  I didn’t have to waste time tuning up and down the band looking for signals.

The second advantage I found with the scope was that I could keep an eye on either side of my run frequency to see if anyone was crowding me.  When I contest, I don’t want to hear adjacent stations and that is why I like to use the 250 hz filter.  If I hear another station and they are not calling me, they are too close.  And sometimes, a strong station can park right next to you, just outside the filter’s passband and you never know it.  The disadvantage to this is that not everyone runs 250 hz filters.  So if someone who is not using tight filters cannot copy me because someone else is too close, then I need to move and find a clearer spot so stations can copy me.  It was too cool to look at all these signals crowded across 20 meters and seeing this nice little open space where I was CQ’ing.

This brings up a couple of other advantages to using the scope.  With the scope, you can find clear run frequencies faster.  And while S&P, you can see the signal you are tuning upon before you hear it.  Have you ever tuned slowly across the band looking for signals while S&P?  You can tune much faster with the scope.  After the Roundup, I received an E-mail from Jerry W4UK explaining another way to use the scope while S&P.  Jerry noted “Let signals collect on the spectrum scope for a few seconds (with TX MARKER on and SET-MAX_HOLD on), then press HOLD. You can then tune straight to the active spots within the span (I use +/-12.5kHz) and not waste time listening for signals where no one is calling.”  I plan on using this technique in the next RTTY contest.

I found one more advantage to the scope that needs more practice.  When operating on low activity bands, such as 10 meters, you can see new signals popping up on the band.  You can’t do this on a crowded band because there are too many signals to keep track of.

The Spectrum Scope is a viable and important tool in RTTY contesting.  It’s simply awesome!

IF Shift

In communicating with Phil GU0SUP before the contest, he mentioned he used the Passband Tuning (PBT) when trying to copy a one station when there was another station causing interference above or below the passband and part their signal is entering the passband on either side.  This is actually IF Shift.  IF Shift is done in RTTY mode on the PRO series using the inner knob of the Twin Passband Tuning adjustment.  I’m glad Phil gave me this tip because it worked very well on a couple of occasions when a nearby station was intruding into the filter passband.  I was able to shift the IF high or low to eliminate  the part of the interfering signal that was preventing me from printing the desired station.  It works great and it’s a feature not found in the Kenwood TS-870.

Manual Notch Filter

When I went from an Icom IC-751A to the Kenwood TS-870 several years ago, the one thing I missed the most about the Icom was the manual notch filter.  The TS-870 does not have a manual notch filter.  The manual notch filter is another way to eliminate presence of a signal inside the receive passband.  The PRO III has an excellent manual notch filter.  Unfortunately, it appears it doesn’t work in the RTTY mode.

Twin Peak Filter (click this link for more TPF information)

The PRO series includes a Twin Peak Filter (TPF) only for RTTY use.  The TPF is a special filter that passes two frequencies – 2125 Hz mark and 2295 Hz space.  It’s based on 170 hz shift.  It’s a very sharp filter centered on two frequencies – mark and space.  The concept is a great one.  (The following are my first original thoughts on the TPF in italics, but I have changed my tune and have had added additional comments after the italics.)  But there are three things that bother me in using the TPF in RTTY contesting.  First, not all stations are using 170 hz shift.  So if a station calls using a shift other than 170 Hz, then copy will be affected.  This is particularly true for stations using 200 Hz shift.  The second thing I found that I didn’t like about using the TPF was the high noise level I had to listen to when TPF was enabled but there was no signal present.  The noise is much higher than normal and this is mentioned in the operating manual.  I found the noise too high to be tolerable.  And found no way to turn it down without actually turning down the level to the headphones to a point where I could barely hear when a signal was present.

The third thing that I found, and although it isn’t a “dislike” but rather an early observance on my part, is that I did not see any improvement of copy of most signals when the TPF was enabled.  I was using the MMTTY decoder, which is pretty good anyway.  I did not try the TPF on extremely weak signals.  So I will need to look at this closer and report back.

It needs to be mentioned that there are three available mark tones that can be used in the RTTY mode – 1275 Hz, 1615 Hz and 2125 Hz.  However, the TPF appears to only works with 2125 Hz mark and 2275 space tones.

Update 2/15/05

After I posted my original comments about the high noise generated by the TPF, I received E-mail from Hisami 7L4IOU who suggested the TPF actually worked quite well when the RF gain of the radio was turned back until a reading of S-9 was shown on the S-meter.  I experiment with this in the 2005 XE RTTY contest and found it to be correct.  Not only did it work, it worked so well I used the TPF on both radios for the last 4 hours of the contest.  During the next weekend’s WPX RTTY contest, I used the TPF 100% of the contest on both radios.

During 2005 WPX RTTY, I tried operating with the TPF turned off on two occasions but quickly went back to having it turned on.  I’m not sure how to describe what happens when the TPF is enabled and the receive RF gain is backed off.  It’s like you are operating on a very quiet band and you are the only one on the band.  It’s very strange and nice.  You hear nothing but the station coming back to you.  This is no noise and no interference (unless someone comes inside the 250 hz bandpass).  Unless someone invades your frequency, the only way you know there are other signals on the band is by looking at the spectrum scope.

Depending upon band conditions and which band you are operating, the RF gain does have to be “tweaked” occasionally for optimum decoding.  What I normally do is watch the FFT display in MMTTY with no signal present and adjust the RF gain until there is just a slight presence of the noise floor in the display.  This means the S-meter reading can be anywhere from S-9 to 20 db over S-9, but I found most of the time the reading was nearly 10 db over S-9.  When a signal is present, there is a tremendous jump in the FFT display and the signal is perfect nearly all the time.  I also found that despite the tightness of the filter, signals with a 200 hz shift did not pose a real problem.

Another observation about using the TPF with the RF gain turned down startled me.  I found that the HAL DXP-38 copied better than MMTTY much more than it normally does.  And several times the copy, even with errors, were identical.  It was a strange observation.  It reinforced my set-up to use the DXP-38 with MMTTY in a “cloned” Rttyrite window.

RTTY Decoder

I did not use the RTTY Decoder during the Roundup because I already use two decoders with WriteLog.  I use MMTTY as my main RTTY decoder and I use a HAL DXP-38 in a “cloned” Rttyrite window for receive-only.  However, if I did not have the ability to use two decoders, I think the RTTY Decoder on the PRO III display would be a good tool when print is missed in the main RTTY decoder on my computer’s screen.  The problem I see with the RTTY Decoder on the PRO III is that the print is too small for my liking and I have found no way to make it larger.

I did use the RTTY Decoder while tuning for the VU4 DXpedition.  When I had my PSK31 program running (I use HamScope) and wanted to do a quick check of RTTY signals, I used the RTTY Decoder in the radio instead of changing programs on my PC (closing HamScope and opening MMTTY).

In comparing the RTTY Decoder in the PRO III to MMTTY, I found them to be very close in copy and could not tell that one was any better than the other.  This speaks well for the RTTY Decoder in the PRO III.  To say it’s at least equal to MMTTY it a very good thing.  But I think I need more testing of this.

Final Note

I sent one of the PRO III’s back to Icom and purchased the other one.  I just didn’t have enough money to buy them both.  I’ve been using my PRO III (as of 2014) for ten years now and it’s still a joy to operate.  You just can’t go wrong with this radio.  I love mine!