Icom 756 Pro 3 Serial Numbers
ICOM 756 and 756PRO W8WWV - ICOM 756 and 756PRO (and PRO II) Greg Ordy Last Update: Wednesday, February 26, 2003 05:59 PM I decided to replace my ICOM 756 with a 756PRO. This gave me an opportunity to compare both radios side-by-side. This page contains my observations.
Additional 756PRO information can be found on the pages maintained by,,, the ICOM reflector (mailing list) at, the and of course, the site. If you have any of your own observations, please email me, and I will add them to the list if appropriate. ICOM introduced the PRO II radio in the second half of 2001. As of this writing, the radio is still quite new, and comments and observations are just starting to emerge. A few of my observations are contained at the.
The ICOM PRO II is an update of the PRO. It completely replaces the PRO, and ICOM has discontinued manufacturing of the PRO, building only the PRO II instead. In my opinion, it a evolutionary update, not a revolutionary jump forward. At this point in time, the radio is starting to be used by amateurs. Detailed use information is just becoming.
Because I am comparing two radios here, it may appear as if one is good and one is bad. I really do not want to give the impression that either radio is bad. In fact, given the cost difference between the two radios, I think that both are well worth their respective prices.
For me, I decided that the upgrade cost made sense because of the equivalent cost of the filters necessary to turn a 756 into a PRO. Of course this is not even possible because the 756 has a single filter slot at each IF frequency. But if there were more slots, it seems as if I would need to add 6 or so filters to be able to get the SSB and CW selectivity choices I would like. At $100 to $200 (USD) per filter, the cost difference between the radios evaporates. On top of that, there is the color display and a number of other enhancements. So, for me, spending the extra money made sense. • • • • • • • • • • • • • • • • • • • • • • • I think we have all learned that S meters are, at best, relative signal strength indicators.
S Units are not a standard. S meters are not calibrated against an absolute signal strength reference. Still, they are all we have to measure signals, and they are often quoted. With two radios it's very easy to compare how each reports signal strength. On both radios, the difference between S8 and S9 appears to be 6 dB, a typical value. Above S9, the meter readings are fairly accurate, which is to say that meter markings track real relative decibel changes.
Below S8, both meters becomes increasingly more sensitive. The difference between S1 and S2 may be as little as one decibel or two. I also found what I call a tracking difference between the two radios. The mismatch was the greatest on 20 meters, where the 756 read the same signal as 8 dB stronger on its meter. The difference was about 5 dB on 40 and 15 meters, again the 756 reported a higher value. On the other bands, the two radios basically tracked.
Their S meters indicated the same strength for the same test signal. The S meter on the PRO is also what I would call sluggish. The S meter on the 756 seems to follow syllables in words, and the dits and dahs of CW. The meter on the PRO moves more slowly, regardless of AGC speed.
Finally, there appears to be no adjustment on either radio for S meter calibration. The meter itself, which reports several different qualities, is driven from a microprocessor.
The meter readings are not the result of analog signals changing, they are the result of a numeric computation. What you see is what you get. Since I made my first comparisons, I have made a closer look at the S Meter. That information is on, and if you have a 756PRO, you might want to check out my software. • I have written about ICOM radios and microphones on another.
With the 756, I found it difficult to drive the transmitter to full output with a dynamic microphone element. I had to use an electret condenser element (or a dynamic element with a pre-amp). Black up shabazz palaces rar. The PRO appears to have more available microphone input gain, and I can drive it fully with both dynamic and electret condenser elements.
• Page 12 of the PRO Instruction Manual depicts the back panel of the radio. The PRO, and not the 756, has an additional jack, the Transverter Jack. This jack has been added directly next to the Receive Antenna Connector.
Both are phono (RCA) jacks. The documentation for the PRO incorrectly reverses the two jacks, Transverter and Receive Antenna. This mistake is repeated every time that either jack is shown in the manual. The labeling on the back panel of the radio is correct.
• The PRO has a transverter I/O jack, the 756 does not. The transverter function is activated by placing a 2 to 13.8 VDC signal to pin 6 of the ACC2 jack. When this is done, the radio receives through the transverter jack, and transmits a -20 dBm signal on the same jack. • This observation applies to both radios.
The front panel has a NB (noise blanker) button, which activates the noise blanker function. There are no additional adjustments. Many people report that the noise blanker does nothing and is a useless control. My observation is that the control is effective if you consider it to be an ignition noise blanker. From time to time, I have ignition (spark plug) noise near the house. This is usually due to a chain saw or air compressor.
The noise blanker is very effective in removing this type of noise. For general atmospheric noise, however, the control does do very little. I suspect that ICOM believes that the NR (noise reduction) control should be used to deal with that class of noise. • The spectrum analyzer on the PRO is much more sensitive than the one on the 756. Signals really jump out on the PRO, whereas the scope can be nearly a flat line on the 756, especially on the upper bands when the band is quiet. At first, the difference was so great that I thought that there must be a change in the fundamental computation of the scope data, in addition to an increase in scope gain. But after trying to carefully watch both scopes at once while changing the scope attenuator on the PRO, I am of the opinion that both scopes are the same, except that the PRO scope has about 15 dB more gain.
The PRO scope does have several scope attenuation settings which can be used if desired. Both scopes are influenced by the pre-amp setting. The scope is after the pre-amp, so increasing the pre-amp gain will increase the scope gain. I found myself often increasing the pre-amp gain on the 756 just to make the scope more responsive. With the added gain in the PRO, I only use the pre-amp to improve the audio, not the scope. The PRO also has a two-color mode that uses a muted second color to indicate the maximum signal at each frequency (while the first color follows the signal). When you turn the VFO, the display starts to recompute the maximum signals.
While this is the factory default setting, I find it to be annoying, and I turned it off as soon as I figured out how to do it. I suspect that this was done to give some sex-appeal to the color display. I don't find it useful, however. • Much has been written and spoken about the so-called audio distortion on the PRO.
Here's my opinion. Using the small built-in speaker is not a good way to listen to the radio. An external speaker, or better yet, an external amplifier and speaker connected to the audio out (not the speaker out) is much better. I have all three.
The internal speaker, an external speaker, and I feed the audio out into my computer sound blaster card where I can route it to some good quality multimedia speakers. As the speaker gets better, the PRO audio quality also gets better. That's hardly shocking. The same can be said for the 756.
Still, there is what I would call a brittle quality to the PRO sound. At the extreme, it's harsh. As best as I can guess, it's due to the digital IF. In some sense, it's a signature of such a large amount of digital processing. In fact, I think that the 756 has a more pleasing sound than the PRO. I would much rather listen to a fat and rich AM broadcast station on the 756 than on the PRO. The PRO filters are claimed to be very sharp (shape factor), and this will color the audio as well, especially when there are a number signals surrounding the desired signal.
I would not be surprised if this phenomena was similar to what happened when CDs were introduced in the early 1980's. At first they sounded crisp, brittle, and sterile compared to analog medium, which was warm, lush and full. I find the CW sound to be the most interesting, especially with using a narrow filter setting. On the 756 (350 Hz filter, 9MHz IF), it sounds like you are listening to a narrow wedge of spectrum. Narrow but natural. When a signal appears, you can hear the character of the transmitter quite clearly. On the PRO, with the same filter width, it's as if you are listening to a computer reenactment of the spectrum.
Of course that's what it is. Narrow but artificial. When a signal appears, it's more of a synthesized replica sound as opposed to the underlying transmitter sound. On several occasions I have looked for weak CW signals and tuned both radios to the same frequency. It seems as if both radios have similar sensitivity. If you can hear it on one radio, you can hear it on the other.
The difference I found was that I could hear the dits and dahs more clearly on the PRO than on the 756. Especially with higher speed CW, very weak signals blur together on the 756. Even if you can hear the signal, you can't copy the text. With the PRO, it is often possible to hear and understand the CW. The edges of the dits and dahs are sharper and cleaner.
In summary, and when comparing just these two radios, I find the 756 to be warmer and smoother, whereas the PRO is colder and more brittle. It does seem, however, that the signals from the PRO are somewhat more intelligible and understandable. It's communication, not HI-FI. • Both radios feature an auto notch which is in the audio chain, after the AGC. While they effectively remove carrier tones from the audio signal, the impact of the (usually loud) carrier on the receiver front-end is unchanged, meaning that the receiver gain is reduced. This often makes the desired signal undetectable. This is no more than the common AF DSP notch.
The PRO, however, has an additional manual notch which is implemented at the IF DSP level, and is before or at least within the AGC loop. Of all of the features on this radio, this is the one feature that I would call amazing. The notch is quite narrow, and one must adjust the knob carefully. But, when you hit the frequency, the tone goes away, and the S meter drops as gain is restored to the front-end. The desired signal again appears. • It is possible on the PRO to read the S meter value from the computer (serial) interface. This is not possible on the 756.
My software works with the PRO. • Both radios feature what ICOM calls triple band stacking registers. What that means is that the radio memorizes three different frequency/mode combinations for each band. You cycle through the choices by pressing the same band button multiple times. This lets you store, for example, a favorite CW frequency, digital frequency, and SSB frequency. Just keep pressing the same button until you get to the one you want. One of the bands is the so-called General Coverage band.
I would like to program my favorite local AM broadcast station, 10 MHz WWV, and 15 MHz WWV. For some reason, neither radio will allow me to get those three frequencies on the general band registers. I think this all comes down to the definition of the word band. We know what that means in the amateur case, but in the general case, it is conceptually the entire receiver range.
But as you turn the dial across the receiver range, in the general band, you do hear, from time to time, beeps, which normally signify band edges. They may correspond to the common shortwave broadcast bands, but I have not verified that. In any case, these beeps do appear to trap a register in a band. So, some frequency combinations do not appear possible. This is a very small point, and I doubt if this is a bug, as opposed to just the way that it works.
But, it is not documented, and doesn't make obvious sense (to me!). • The 756 has audio speech compression, whereas the PRO as RF compression. Only the PRO has a meter position that indicates the compression amount. The manual suggests between 10 and 20 dB of compression. I have found that much lower settings are effective without sounding like a typical compressor (jet engine in the shack). It should be remembered that I use a headset microphone that is very close to my mouth.
• The PRO has a built-in voice recorder. The 756 does not.
Note, however, the PRO voice recorder is not very useful. On both receive and transmit you can record up to 4 different segments, each up to 15 seconds long. The received segments can only be played on the speaker, and the transmit segments can only be transmitted and reviewed on the speaker. Two additional capabilities would have made the recorder a much more useful feature. First, the ability to play back received audio on the transmitter (let your friends hear how they sound at your place), and the ability to trigger the transmit messages from the computer interface (to be done so by logging software). 
Without these features, the voice recorder is basically a gimmick. The Yaesu FT-920 has about the same problems.
Another great variation would be to allow the voice recorder to record continuously, and be able to replay the last 15 seconds on command. I would really like this for capturing DX exchanges, where I would like to make sure that my call was copied correctly. Of course you never know that the DX is coming back to you until it's too late to hit the record button, so you really can't start recording on cue. It's much better to be continuously record, then stop recording after the important part of the exchange. • This is one control that does not impress me very much on either radio.
The function certainly seems nearly identical on both radios. It appears as if the intent of this control is to remove atmospheric (and other random) noise from a desired signal.
Icom 756 Pro 3 For Sale
As you increase the reduction value, the noise is indeed scrubbed away, but so is the readability of the signal, especially on SSB. The control changes the signal/noise sound, but to me, it never really improves it. I find the control most useful on low settings, around 9:00 o'clock.