Reviewand commentary on the ICOM IC-756 transceiver
(Revised & updated version, April 14, 1999)
Serial# 03795 , FL-222, FL-223 installed
Reviewed by Matt Erickson KK5DR
First of all, let me say that this review will NOT, be like the ones seen in most ham magazines, mainly because I have no advertisers to protect. So, no punches will be"pulled".
Iím writing it from an average users point of view, not an engineer, or a RF lab tech, with use of allot of high tech test equipment. I am the typical, average ham that likes high quality gear.I like abit of practical application testing, and a little humor too.
My background, as a reliable reviewer; I have personally owned about 55 HF rigs, of all makes & models, many are good, some not so good. In the Icom brand I have had the IC-720A, 730, 735, 751A, & 765.I also took 4 yrs of electronic school. I feel this qualifies me to make the statements I will make in this review. Please keep in mind that my statements are my own, based on my own thoughts & opinions, here for your consideration and judgment. I will not bother with the lab test results, which have already been published in QST.
AT FIRST GLANCE;
The IC-756, is a handsome looking rig, with a nice finish. The"stamped" in ICOM logo on the top cover, is a nice change, but must have been abit of an expense to tool up for. The paint finish is a rough "fingerprint proof", flat black. It appears to be a "powder coat", baked-on type, very tuff !
Very few protrusions are found on the rear of the rig. The entire back end of the unit is a large heat sink of bare cast aluminum.
The bottom side is also the same finish as the top side. It has a"drop lip", in the front, and flip down legs to tilt the rig up at and angle. This unit did NOT have any rubber on the feet, so, the rig will slip easily on a smooth table top. A nice set of "grippy" rubber feet would really help keep this rig in place when I plug in or out the headphones, or paddle keyer.
The"Bizniz end", front panel;
If you have seen pictures of an IC-781, or seen one in person, youíll see where the inspiration for the front end of the 756 was born, itís very similar, A smaller version of the BIG 781. With allot of influence from itís big brother the IC-775. Imagine if a 781 & a 775 mated, the 756 is the likely offspring.
I wonít go into great detail about the front controls, like the "BIG Magazine reviewers". Most are self explanatory, and common to all ham rigs now days. The VFO knob has a good "feel" to it, personally I like a little more weighted "flywheel"effect on a VFO knob. But, generally the 756ís is good, and has a easy to adjust, front panel "drag" setting.
The meter, is very good, and has good accuracy. The back lighting of the meter and LED indicators, are adjustable via a menu setting. The tuning rate is also controlled by what is now widely know and used as
"fuzzy logic", meaning that the tuning of the VFO knob, increases or decreases the tuning rate with the speed of the spin, applied to it. Itís a standard feature on almost all late model rigs.
KEYER plug on the front of a rig ! WOW!, but itís not a new concept, thatís the way rigs were back from the beginning of amateur radio up till about the 50-60ís. Itís about time the modern manufacturers got back to it.
High contrast, hi res. LCD, back lit, and"LOADED" with info. A feature I liked right away, is the fact that you can see in one look, all the frequency info you need, VFO, memories, sub recv. All in a single glance!
The Spectrum Scope, is highly useful, and has a wide enough span, to see if a band is active at a quick look. The lowest span, could have been lower, to allow for a more critical analyzation of signals . The vertical gain & sweep should have been calibrated with S-meter readings, but itís not, this would have been even more useful. A variable refresh rate on the sweep would have been a nice feature too.
The key pad is a little "tight", for those if us with big American fingers. Itís a pretty standard layout , and functions.
A look inside the box
The chassis is 1/8 inch thick cast aluminum, with cast partions between the various compartments. Nearly the entire chassis is a integrated heatsink. Besides the metal shielding provided by outer covers, there is a shield plate on the inside of the top and bottom too. A nice touch !
The circuit boards are nearly 100% SMT, or Surface Mount Technology. They are very very high quality construction, and the soldering is of the highest quality also.
The construction is of a type that I have seen only in NASA space launch equipment. Itís highly reliable, and very efficient, generating minimal amounts of heat. ICOM, has raised the bar, on the level of design, and construction of HAM equipment. If I were to place a single word here to describe it, I would say; "EXQUISITE!". I am very impressed.
Noise Blanker (NB) First of all, I got to say that I found this function to be mostly "useless", not able to blank noise of any type. It had little or no effect on noise for which this function was designed to remove or decrease. Comparing it to the NB, on my YAESU FT-990, the 990 can blanker nearly any noise, even at extreme levels. Of course the 990, has a variable level NB setting, something that is missing from the 756. If I had designed the 756, I would have made a menu setting for both level and width for the NB. The most noticeable effect of the NB, is distortion it creates by being turned on. A disappointing look at the NB function.
This function works well, but can easily be over done. I was puzzled by why the control is taking up valuable front panel space. Compís are usually "set & forget" type settings, in my view. it should have been another "menu" setting, and limited to a max of 15db compression. This would prevent most of those distorted "DX" guys, from getting to wide. Any thing over 15db compression, is DISTORTION !
RF/SQL RF gain & Squelch
The default setting of both controls sharing opposite halves of the same knob, got abit confusing to me, so, I shut the SQL off. Would be a good candidate to place on the speech comp, control I moved to a menu in my "redesigned" , 756.
TWIN PBT Twin Pass Band Tuning
This control is a concentric inside/outside knobs, and operate both the 9mhz & 455khz IF Pass Band tuning, with a digital on screen indicator of the settings. It WORKS EXTREMELY WELL! I really like it ! With the 2.4khz & 2.8khz it works great ! I installed the FL-222 1.8khz (455khz IF) filter, and the FL-223 1.9khz (9mhz IF) filter. This allows numerous combinations of filters that can be used. Then I listened to 80 meters, during a tremendous storm of static and storm crashes. For several hours I "dug" signals out of the "muck", using the narrow filters, the wide filters were nearly unusable under these conditions. The narrow filters donít give a very good audio response, but they mean the difference between copy and no-copy in very rough conditions. A truly useful & powerful interference fighting tool.
Works like the auto notch on the AF, outboard type units, but itís faster, & distorts the signal much less. I did notice that the A.N. desenses abit on strong signals, mainly because the circuit is after the AGC stage. In this way, it allows the receiver to be desensed by the notched signal. If it had been done like the 775ís A.N. , it would have been far more effective, with little or no desensing. The Auto Notch does a nice job anyway, and performed as well as my TIMEWAVE DSP-599zx out board AF unit, in the auto notch function.
About 10db short of having adequate gain level. With the hand mic in use, I found I had to use nearly all the mic gain range to get enough drive for full output. When I used the SM-20 desk mic, which is amplified, I was able to lower the mic gain setting on the rig, to about half way up, for my style of operation. The mic plug has a pin providing 8 VDC @ 10ma MAX. ! This is to power the amp in the mic, but for many non-ICOM amplified mic will exceed the current limit. That will damage the regulator in this circuit. Suggestion to ICOM; raise the limit on this circuit to about 100ma. A resistor buffer will protect from a short circuit too.
The hand mic gives good clear audio, and received good audio reports on the air.
The SM-20 desk mic, has a low cut control, that cuts about 4db off the low freq end of the audio. I spent a few hours with a friend, on the air, setting up this mic, to sound like my natural voice, using the menu Bass & Treble settings, finally settling on +2db Bass, & +6db Treble, with the low cut, off, on the mic. No two voices are exactly alike, so everyone would have slightly different settings.
NR Noise Reduction
Works much like the AF outboard units, in the removal or reduction of random noise, with a bit of a difference. There is a level adjustment, that allows you to set the level of aggressiveness of the NR .
This allows less audio "echo", reverb distortion on the signal. I found that the NR, did very well, and out performed my TIMEWAVE DSP-599zx in the random noise removal area. A very good system .
Adjusts the frequency of the receive CW signal & the sidetone, independent of the actual TX offset freq. which on the 756, is 700hz, the same as most all other modern rigs. It works well, and is a smooth control.
APF Audio Peak Filter
Work exactly like manual notch filter, only in reverse. This control aligns precisely in the same position as the CW Pitch control.
I ran into a bizarre glitch in this area. A short time after I got the rig on the air. I found that the CW sidetone would not change in frequency as it should when the CW pitch control is moved. Then a few days later I checked into the ICOM Net on 20 mtrs, to query the net about this problem I had on my 756. Other stations reported that their rigs operated properly. I checked my rig again, and the trouble had "cleared" itself, and the rig was operating as the others on the net were. We could only sermise that, do to the RAM / ROM operating areas, and the way these areas are cleared and reloaded with a "fresh" program each time the rig is powered up. The problem had existed on the RAM area, while the rig was operating. and a "new" program was loaded from ROM, the next time the rig was turned on. The "glitch" was cleared and the rig operated as it normally should. A "SELF REPAIRING" rig, EXCELLENT !!
CW TX Brk-in
These are "on-screen" controls. I like them, separate from the normal VOX controls. This is a nice way to do CW controls.
CW TX on the air
The 756, has a nice clean CW note, very pure. During full brk-in operation, I could detect only the very slightest "chopping", of the CW notes during sending. There is also abit of AGC "pumping", meaning that between CW notes, the receiver fails to recover fully. Falling short of full receive gain level, by a few db, to nearly 6db. Comparing it to my FT-990, at full brk-in, the 990 does it much better, coming close to the "legendary" TEN-TEC full brk-in performance.
Weighting is good for me at the "default" setting of 1:3 .
CW Memory Keyer
This is a great feature, very usable for Field Day, or Contests, if your into that type of thing. The memory keyer banks are programmable through a menu, by panel keys, no CW key needed. It would have been really cool if a 10 minute ID function of the memory keyer had been added.
What you hear on it, is what is going out on the air. Very accurate sound. I listened on an outboard receiver, and it sounds exactly the same as the onboard Moni. All rigs should have a feature like this.
Clock on screen
A nice feature, I set it to UTC, with WWV. I checked it 2 weeks later, and the clock was only off by 1 second. The clock feature would be really cool if it had a 10 minute ID function . Triggered by a front panel button, to enable it, then disabled by toggling the same button off.
Good for "zero beating" the rig, makes it real easy. I set the rig on WWV a few hours after first powering up. The Cal marker showed me that the rig had an over all freq. error of about 15-20hz at 30 mhz. I was able to "tighten" this up to about 5-10hz. The rig has a great deal of freq. stability, at normal room temperature. The TCXO option is only needed if the rig is to be used in "EXTREME" environmental conditions, such as Arctic expeditions, or desert use. Under normal conditions, the addition of the TCXO unit to the rig, would be a unnecessary extravagance.
!/4 turn Tuning
Here is a feature that the digital operator is going to love. When you are in RTTY mode, the 1/4 turn option is on the screen. When activated it slows to tuning rate to only a few hundred HZ per turn of the VFO knob. In addition one can turn on the 1HZ digit by pressing and holding the TS button, with the 1/4 turn on also, tuning is EXTREMELY slow, and precise. A useful feature.
I like using Solid State rigs on 10mtr AM, itís a challenge to make them sound good. The 756 was pretty easy to get to sound good. The 756 is abit enigmatic when it comes to the proper carrier level for AM.
With a little work, I found that for some strange reason, the 756 does not forward modulate, unless the carrier is between 20-25 watts. To little, or to much, and it reverse modulates.
On the air Audio reports were good to excellent. The audio is abit punchy to some. I believe this is due to the nature of the TX audio on AM. Itís digitally derived, mathematically perfect. Not quite as smooth as old tube AM equipment, but very clear. On RX, the 15khz & 9khz cascaded filters are super nice to listen to on AM. In noisy conditions, narrow filters are needed. Broadcast listening on the 756 is a pleasure, just turn back the RF gain, put on about 12-18db attenuation, and kick back to some really nice sounding broadcast AM audio.
There is nice "texture" to the RX audio, smooth sound. On SSB the 756 is totally digital, in detection of signal, shaping & processing too. I find the 756 to be a pleasure to listen to, with little or no listener fatigue. But I did have to run at least 6db of attenuation, and slightly less than full RF gain. This receiver is "HOT", one of the hottest Iíve ever encountered, so itís required to run the receiver at less than full strength , to keep from over powering it with noise and strong signals. This is only true on the HF bands, on 6 meters the receiver is "HOT", by design, to pull in those weak signals found there. Six meters is probably the only band that the receiver can be run full out at max. sensitivity.
On ten meter FM, the 756 operates about the same as any other HF rig, with the exception of the scopes usefulness here is a plus. Use the scope to spot "elusive" repeater or simplex activity. The receiverís "super" sensitivity doesnít hurt either.
The 756 has a very active SWR protection system. I found that at a SWR of about 1.5 :1, the power output is reduced to 50-70 watts. By activating the internal tuner, the output returns to 100 watts, full power.
At a SWR of 2 : 1, the auto tuner automatically activates, if the setting on the menu is on.
By far, the fastest in the west, as in "lightening" fast. Works on receive and 6 meters too.
Very quiet. It runs every time you transmit, and for a few seconds after TX also. The chassis being a HUGE integrated heat sink, a large noise fan is not needed in the 756. This is one cool running rig !
Optional filter slots
Two is not enough, four would be a good number. Two in each IF would really enhance the rigs capabilities.
Using a non-ICOM amp, usually requires a ALC feedback line, to limit the drive of the amp. When I used the FT-990, with my ALPHA 76A, the ALC level would indicate on the meter, but that was all it would do. There was no reduction in drive, so I was forced to use the RF power output control on the rig, to control the drive level. With the 756 hooked up to the same amp, the ALC works great, output is limited to the level I have preset on the amp. I can run the power level control on the rig, at full out, and the rig drive level is nicely controlled and limited by the feedback voltage sent back to the rig from the amp. ICOMís ALC system works like an ALC system should.
RX Phase noise
Here are a few words on phase noise, on the 756 receive. There is a very small amount, but it can only be heard when in the presents of a strong signal, within 10khz of your freq. Mostly, phase noise can only be heard coming from a signal with strong phase noise components transmitted in it. This is usually the case of "older" PLL type rigs, that have a less pure synthesizer signal.
You really have to listen close to even detect the small amount of phase noise that rarely surfaces. When your more than 10khz away from any "dirty" signal, no noise is heard at all.
All PLL rigs have some phase noise, even my FT-1000D had some. The 756 noise, is livable and manageable. As Direct Digital Synthesis gets better and more pure signals, phase noise is going to become less and less of a problem. Unlike the early PLL rigs, that were "LOADED", with phase noise. As "dirty" older PLL rigs are gradually retired, and DDS rigs are improved, phase noise will go the way of "spark gap".
Hints and Kinks
The 756 has abit of a "light-weight" amp keying relay. Rated at only 16VDC @ 2 A. It is subject to damage if operated at higher levels. The damage being contact "fusing", due to high currents and or keying back-pulse transients. Back-pulse transients are a result of the collapse of the T/R relay magnetic coil field, sending a inverse current back down the keying line, jumping the contact gap, arcing and fusing is closed.
My ALPHA 76A , keys with 24VDC @ 160ma, which is not that much compared to other amps. So, I designed and built a "damper" circuit, to use in-line with the 756. The damper consists of a 1ohm 5 watt resistor in series with the keying line, also a pair of silicon diodes in front and back of the resistor. The diodes are placed anode to the key line, cathode to ground. These diodes cancel out any back-pulse that might come down the line, shunting it to ground. Two diodes can handle up to a 4A pulse, and the likelihood of both diodes failing, is very remote. The resistor handles the current in-rush, when the line is keyed. It also ballasts the line to a limited current level, for a given voltage. In addition there are two disc caps. from the line to ground, .01 & .001mf, for RF by-pass purposes. All placed in a metal box with the proper connectors mounted on it.
After a month of using the amp and rig with my "damper" in-line, there is no problems with the rigís keying relay. WARNING ! I would not depend on this circuit with amps that key with 110VDC, ie. SB-220/200 .
I would say the safe limit for my "damper ", is about 28VDC @ 1A.
I did look into a "improvement " inside the rig, to the amp keying relay. If a person needed to, he could replace the existing relay, with a solid state relay from RADIO SHACK, that can handle 200VDC @ 4A.
There is plenty of room in the area of the existing relay. The RS relay activates with only a few volts and very low current. A added benefit is that the relay is silent, & virtually instantaneous. I might be tempted to do this modification, once my 756 is out of warranty.
It has been said that ICOM HF rigs have a noise audio amp chip, making it "hiss", noticeable. The 756 is no exception. It is not as bad as some of itís older brothers, but it still has the same defect. I have a simple fix for it. The problem is that the audio amp hiss is a product of the drive level, the lower the volume, the less the hiss, but the level required to remove the hiss, is to low for most people to hear signals at.
By placing a outboard audio DSP unit in-line, the volume on the rig can be reduced to get rid of the hiss. Then using the audio amp in the DSP unit, the volume can be brought back up to a level that can be heard, minus the hiss. I use a TIMEWAVE DSP-599zx, and it works great to this end. The DSP unit also has other benefits as well. One can "tailor" the audio more than with the rigís controls alone.
Of Rumor & Myth
There has been some discussion and conjecture about a "updated", 756 PRO, that might be produced in the near future. ICOM is denying this rumor, and no "industry insiders", are able to subtanciate it. This may be a "trial balloon" sent out by ICOM themselves, to "test the waters" and find out if the market will support the production of such a rig. The 756 is a very popular rig and the market might support a 756PRO. This story is not over, wait and see what the outcome will be.
A Hidden Menu ?
It has been published on the internet, that there is a hidden menu on the 756. The procedure that was posted is as follows; Cut D16, power up the rig with the A=B buttons pressed. This is likely false ! There is NO A=B buttons on the 756 ! Secondly, a hidden menu is a "software" function, WHY cut a diode ?? This smacks of "disinformation". Donít do it, or try it ! It may damage the rig, and if it doesnít , it surely will not do anything .
The ICOM 756 is a very good rig, a significant improvement over "older", analog rigs. If your serious about your SSB and want a rig that can really "dig" in the dirt and pull out the weak signals under nasty conditions, then itís for you.
However, if your a serious CW op., then you might not like it as much, as some of the other rigs that are designed with CW as the primary concern. If your a casual CW op., like myself, youíll say that the 756 is as good as it needs to be for your use in that mode.
SSB is the primary design concern that ICOM put into the rig, and it does it very well indeed.
In the end, Iím pleased with my purchase of the 756, and I think it will have a place in my shack for many years.
Addendum April 1999
After using the rig a while, I did finally find a noise type that the NB, could remove, itís a slow pulse type, like ignition/sparkplug noise. The frequency range of the NB, is very narrow, and is active only at higher amplitude levels.
After disscusion with the other 756 users on the ICOM net, it was the conclusion of the group, that the 756 NB, should have had a level and width adjustment on the menu, but again we run afoul of the design budget limits. With these features added, it may have cost some other more useful item.
The LCD display may have vertical lines that sweep across the screen from time to time, this is a normal occurance, usually happening when the rig is cold, or the air in the shack is very cold. After the rig is warmed up for a hour, this should dissappear.
The display may not light up when the power is turned on, but it will come on in a few seconds after the rig is powered-up. This problem does not happen often, and is normal, but if the screen does not light up with-in a minute of two, it is more serious trouble then.
An article in APRIL 1999 QST, stated that the display could be made to change colors with a computer control program change, is total fiction. The display can not be changed from the monochrome that it is made to display. APRIL FOOLS !
Is the 756 for you ?
If you wish to find out more about the rig, from those who use it, tune into the ICOM users Net, on 14.317mhz, at 1700 Z Sunday, and ask them. There are lots of these rigs on the net, including mine.
Best of 73 CUL