I looked at both the 590 and the 7410 to replace a FT1KMP that was filtered up with IRC roofing done as well. I ended up with the 590 cause the test results seemed better on three reviews done, well two, the ARRL and the RadCom review plus Sherwood's tests but all these tests were don on CW, most of my Op is done on SSB were the differences might not be as great. I didn't go with the 950 cause its review compares more to the 746Pro I had and not in the same league.
I only wish I would have been able to use the Icom cause the DSP might have had better shape factors in the 7410, they have been doing DSP I believe longer than anyone out there but the numbers only tell par of the story. I find the 590 more than ample on SSB, the front end doesn't seem to get crushed as much as the FT1KMP, it seems to hold its own on a crowded band plus it has a great pre amp like the Icom's always have had when you need it but I find I really never use the pre amp cause the standard sensitivity is more than enough. The DSP filtering is very good but I feel the Icoms nail it when it comes to the amount of adjustments you can make over the Kenwood but Kenwood if there smart might fix that with firmware some day soon I hope.
On SSB you can bring the selectivity down around 1200Hz with good copy on voice signals, on CW its outstanding and hold a close second to K3. Its a very easy radio to learn, almost zero learning curve but the Icom is also that way.
The computer software is free were Icom wants $100 for that option along with charging you extra for the roofing filters as well which the tightest roof is 3Kc were the 590 has 2.7Kc and 500Hz as stock on the bands were you need them the most (160,80,40,20&15) but even the up convergence design used on 10 is more than FB for that band. For the current price of just over $1.5K and some dealer is giving a 25amp switching supply with the radio its hard to justify the 7410's over $2K price. I think if I only wanted Icom in my shack I would get the latest serial number used ProIII and install the IRC roofing filter in that rig, that way I'd have the band scope plus a decent RX for SSB when the bands get busy, I feel Icom missed the boat on the 7410, they could have had mid market leader if the RX was designed better but Kenwood spanked more than a few companies with the 590. The 590 is not perfect but its dam good, there is some room for subtle improvements that could be done in the firmware but that's if Kenwood wants to invest more time in firmware R&D but with there TS990 coming out that might happen. They also should look at bringing another HF rig to that around $3K market as well, kinda a rig that would ruffle Yaesu's feathers with the FTDX3K that should be out soon but who knows. What I find strange is Icom's 7800/7700/7600 doesn't test as well as the 590 in some very important area's and the 7410 tests as well as there top radio does, they need to get into the lab and start to look at there competition again.
I didn't mention the TenTec but I feel its a very simple radio and way overpriced but does good in the testing. The K3 is also a fine rig but you gotta love that Heathkit look and constant firmware improvement's plus the sound of the RX on receive, I dint care for the RX audio on SSB but that's my taste and on CW they do seem to be the King along with the FTDX5K's Logged.
The 7410 is better than the proIII, but neither is as good as the FT-950 and the TS-590. I would place a 950 well below a 590 or 7410. Fortunately, I posted a link that does not support what you said. What ever 'thunder' the 950 has was lost when 590 shipped and the 7410 is basically a improved pro leaving 950 bringing up rear I gave the poster a link that he could determine that for himself. You are giving him hot air.
If you have any stats that support your findings, then stop babbling and post them. I posted the Sherwood Engineering stats. The last time you were babbling, the FT-950 was not listed with the tested radios. Since then, it was tested and posted and much to your chagrin, it tested far better than the detractors would have liked. The 7410 is better than the proIII, but neither is as good as the FT-950 and the TS-590.
I would place a 950 well below a 590 or 7410. Fortunately, I posted a link that does not support what you said.
What ever 'thunder' the 950 has was lost when 590 shipped and the 7410 is basically a improved pro leaving 950 bringing up rear I gave the poster a link that he could determine that for himself. You are giving him hot air. If you have any stats that support your findings, then stop babbling and post them. I posted the Sherwood Engineering stats. The last time you were babbling, the FT-950 was not listed with the tested radios. Since then, it was tested and posted and much to your chagrin, it tested far better than the detractors would have liked. I am not babbling.
Electric guitar history. The 590 redefined its 'class' and is the one to match or beat in that class and the 950 is not one of them that is even its equal. Wishing does not change that. Even 590 will likely be outclassed in a few years as DSP is still maturing. Many assume that the mere presence of DSP assures excellent performance but this is not true.
It is the quality of the design and hardware used that determines its true potential. No software or firmware will overcome design limitations. The 7410 is better than the proIII, but neither is as good as the FT-950 and the TS-590. I would place a 950 well below a 590 or 7410. Fortunately, I posted a link that does not support what you said. What ever 'thunder' the 950 has was lost when 590 shipped and the 7410 is basically a improved pro leaving 950 bringing up rear I gave the poster a link that he could determine that for himself. You are giving him hot air.
If you have any stats that support your findings, then stop babbling and post them. I posted the Sherwood Engineering stats. The last time you were babbling, the FT-950 was not listed with the tested radios. Since then, it was tested and posted and much to your chagrin, it tested far better than the detractors would have liked. I am not babbling.
The 590 redefined its 'class' and is the one to match or beat in that class and the 950 is not one of them that is even its equal. Wishing does not change that. Even 590 will likely be outclassed in a few years as DSP is still maturing. Many assume that the mere presence of DSP assures excellent performance but this is not true. It is the quality of the design and hardware used that determines its true potential. No software or firmware will overcome design limitations. Still waiting for the stats Logged.
Brand new in box Icom IC756 Pro III. Basically unboxed, inspected, and then placed back in the box and in the closet. Serial number is: 3204610. The item “Icom IC 756 PROIII Radio Transceiver NIB New in box late serial number” is in sale since Thursday, April 28, 2016. This item is in the category “Consumer Electronics Radio Communication Ham, Amateur Radio Ham Radio Transceivers”. The seller is “drweir1″ and is located in Pittsburg, California. This item can be shipped to United States.
![Icom 756 Pro Iii Serial Numbers Icom 756 Pro Iii Serial Numbers](/uploads/1/2/3/7/123757615/537999206.jpg)
Brand: Icom. Model: IC 756PROIII.
Supported Modes: AM.
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.
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). 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.
Icom 756 Pro Iii Serial Numbers
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. 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. This is helpful for taking the edge of noise bursts while ragchewing. I certainly don't see how this control could be useful in weak-signal work. I looked for a number of what I would call weak signals. These included CW signals on an otherwise dead upper band (no background noise at all), and weak SSB signals in the 75 meter DX window (little background noise). In all cases, the radios had very similar sensitivities.
If I had to pick the more sensitive radio, however, it would be the 756. Please note that I conducted my tests with both pre-amps off. Since the pre-amps appear to add the same amount of gain, I do not believe that the pre-amps would change my comparison. Given the brittle sound of the PRO DSP, and coupled with the slight edge in sensitivity going to the 756, and assuming the same filter bandwidth in both radios, I would prefer the 756 (receiver) over the PRO. It's close, but the warm and lush analog 756 is very appealing. The IF DSP needs to offer just a little more to truly pull ahead of the established analog technology.
The conflict is that the 756 has a single filter position available at each IF (9 MHz and 455 KHz). This means that it is impossible to get as many filter choices as I would like. As a compromise, I would put the 350 Hz filter at the 9 MHz IF, and a 250 Hz filter at the 455 KHz slot. The default SSB filters would be used. In my opinion, this would give the 756 SSB, wide CW, narrow CW, and RTTY filtering. It would be a very appealing configuration. The primary appeal of the PRO is the large number of filter width choices.
I believe the number is over 40. Given the number of free filter slots in the 756 (see the comments), the PRO has substantially more filter choices. The way that the radio is set up, it is convenient to think of three filter settings per mode. Each of these settings can be changed, but I found myself picking my three favorite settings and then not changing them that much. On SSB, my most common filter settings are 2.8, 2.4, and 1.8 KHz. These values are close to the factory defaults.
I find myself lowering the center frequency, however, in order to better match the typical male voice, and to reduce the high end hiss. The filter selection does make quite a bit of difference. Normally, I'll use a 2.4 KHz filter for DXing, and 2.8 KHz for ragchewing. When the local signals are good, it's nice to be able to crank up the bandwidth and get a fatter sound, approaching AM or FM.
The real value of the filters comes in when an interfering signal enters the passband. On many occasions I have had hash and garbage really eat into the desired signal. By going to 1.8 KHz, the interference is clipped off. Coupled with the manual notch to remove carrier tones, it's a powerful combination. One can go below 1.8 KHz when necessary. I do find myself reaching for the filter adjustments and it's great to be able to adjust center frequency and width. Very flexible and powerful.
I no longer accept adjacent channel interference, I try to get rid of it. It can usually be done.
On CW, my most common filter settings are 1.2 KHz, 350 Hz, and 100 Hz. I think I use the 350 Hz setting since that's the filter width I have in the 756, and I have wanted to duplicate that in the PRO (for comparison tests). I thought at first that I would always use a very narrow filter.
But in practice, I like to start off wide, and go narrower as needed. In some sense, the wider CW filters are used for spotting, that is finding activity. Here's where the more sensitive spectrum scope on the PRO is very nice.
When using a narrow filter (100 Hz, for example), it is easy to simply miss signals. The scope will show me that a signal is there, and I rock the VFO back and forth in order to find it. When you get very narrow, tuning can be critical.
That may be the time to turn on the RIT, in order to make sure that the transmit frequency does not change. On SSB transmit, there are three selectable widths. It's hard to understand why one would leave the wide setting. I should explain that I have never been a fan of the classic narrow bandwidth contest audio - it's no fun to listen to for any length of time.
I do admit that it does have its moments. I have had the following scenario happen more than once. I will be one of many stations calling some rare DX. After perhaps a dozen calls, I will finally realize that under the existing conditions, my signal strength is nothing special, I am one of many. I'll then (hopefully) remember to narrow my transmit audio bandwidth.
In many cases, I've made the contact on the next call or two. I can only believe that the additional punch made the difference.
I wish that these radios had a carrier offset adjustment for SSB transmit, like on some Yaesu radios. After over 30 years on HF, I finally tried 6 meters in the summer of 2000, with the sunspot cycle near its peak. It was quite a bit of fun. Both radios support 6 meter operation.
What I wanted to share on this page was the high value of the spectrum scope on this band. When an opening occurs, the scope makes it very easy to find the activity. This is especially true on SSB, where stations tend to gather at 5 KHz spacing on and above 50.125 MHz. It's easy to keep track of all of the activity on the band.
Apparently the phrase Twin Passband Tuning has been an ICOM signature on a number of radios. It is the ability to exploit IF shift at two different IF frequencies from one set of concentric tuning knobs. The effect it creates is the ability to both modify (in width) and shift the effective passband. The 756 even presented a little picture of the virtual passband, which changed as you adjusted the knobs.
ICOM has retained the Twin Passband Tuning terminology on the PRO, and I don't think it makes much sense. First of all, the phrase is technically incorrect since one is no longer shifting twin passbands. All of the adjustments are within one IF within the DSP. Of course this is actually a simplification of the way to think about filters, since now we have what we always wanted, which is to talk about the filter in terms of filter bandwidth and filter center frequency. In my opinion, the PRO knobs should have been labeled Bandwidth and Center, as opposed to Twin PBT. I think they didn't want to scare people away who might think that their big feature was removed.
It isn't removed - it's better, but they used the old language. This is just a small user-interface issue. If you go into the filter adjustment mode on the PRO, you have a complete picture showing the filter width, starting frequency, center frequency, and top frequency. The 756 has a feature called APF, Audio Peak Filter. It really is nothing more than an audio filter used with CW. It has 3 selectable bandwidths, 80, 160, and 320 Hz. The center frequency is also adjustable to match your favorite CW pitch.
This feature is not on the PRO, and it does not need it, since one can create an IF filter which is as narrow as 50 Hz. An IF filter should always be better than an audio filter. The 756 lets you select one of three (slow, mid, fast) AGC time constants on non-FM modes. The PRO gives you the same three selections, but the underlying time constants can be user specified in a configuration table. It seems like there is more to adjust here than one would ever need. Much has been written and said about the so-called intermod problem on the PRO. Part of the problem is identifying exactly what it sounds like.
Here is a message from the by Sean, K3XT, that is a good description of how to hear the problem for yourself (or at least one version of it) (reprinted with permission). I was on 40m this morning and ran across K8JW saying how he returned his Pro because of unacceptable DSP intermod problems in crowed bands. He said he contacted Icom and they refused to acknowledge the problem. He told me how to hear these intermod products. I tried the below procedure and sure enough you can hear them.
Note, this is intermod products not an audio distortion issue.SSB- Select SSB filter of choice. Tune VFO to a quiet area of a band that has S8 or stronger signals on either side (+- 10 KHz) of your VFO frequency.
Set your band scope to +- 12.5Khz to see these signals transmitting. Put on your headphones (in my case Heil pro set that have a good bass response). Turn the audio (AF) knob full counter clockwise (off) then turn it clockwise till you hear a faint pop (7:30 position)(DSP audio has just kicked in). You can hear a faint low tone rumble of the various mixing products of the adjacent signals. You can see the signals on your scope corresponding to the intermod you hear.
These intermod products are very faint and is a non issue because as you turn the volume to a normal audio level (9 o'clock) the noise and/or signal quickly masks these intermod products. The intermod products do not get louder as you up the volume control.
It is a different story on CW.CW- Select CW filter #2 (500Hz). Tune VFO to a quiet area of a band that has S8 or stronger signals on either side (+- 10 KHz)(actually, one signal will do) of your VFO frequency.
Set your band scope to +- 12.5Khz to see these signals transmitting. Put on your headphones.
Turn the audio (AF) knob and set your volume to a comfortable level, in my case it is 9 o'clock. At this point you will hear what sounds like key clicks that are very low in frequency.
You will hear these intermod products even at normal volume levels. Even if you tune the VFO to a CW signal, you can hear these low level intermod products between the pauses of the CW characters of the station you are listening to. I can not hear any of these intermod products with my SP-21 external speaker, only with my headphones. Serial number for my Pro is 1698. Sean - K3XT I can hear these artifacts on my PRO as well. I don't think that the word intermod technically applies because intermod or cross modulation requires two signals.
These artifacts can be heard with a single signal. That's really not important, since the sounds are real. They are weak, but they are there. In my opinion, these sounds are part of the overall brittle sound that I hear from the PRO. Normal SSB and CW signals are surrounded by little clicks and pops and thumps.
I believe that they are artifacts of the IF DSP stage. Again, a signature of the technology at this point in its evolution. These sounds are not found on analog radios, at least the ones that I have used, including the 756. I also find that these sounds do not interfere with copying the desired signal.
They are a distraction at best. Since this page is about comparing the 756 to the PRO, I thought I would conduct a CW keying test. I set up my 756 to transmit into a dummy load on 28.100 MHz. I tuned the PRO to the same frequency. By adjusting the transmit power level, and the receiver attenuator, I was able to create signals at three levels, S9, S9+20 dB, and S9+50 dB. I transmitted a string of dits and tuned the PRO above and below the center frequency noting when the CW signal was no longer detectable in a pair of headphones. I then reversed the setup, and transmitted on the PRO, and received on the 756.
Here's what I found. The detectable bandwidth is listed in the table. Both radios had a 350 Hz CW filter setting. S9 S9+20 dB S9+50 dB 756 ± 2.25 KHz ± 8 KHz ± 25 KHz 756PRO ± 8.5 KHz ± 10 KHz ± 13 KHz For very strong signals, the 756 is twice as wide as the PRO.
An average S9 signal, however, can be heard ± 8.5 KHz on the PRO (only ± 2.25 KHz on the 756). The artifact that is heard is very weak. It does not affect the receiver gain, and it does not obscure real signals.
The IF DSP on the PRO makes it a new radio and new experience. For me, I can live with the artifacts in order to get so many filter positions. The artifact sounds are unexpected, but I do not find that they interfere with copying the desired signal, even when it is a weak CW DX signal with many callers only a few KHz away. Both radios feature adjustable bass and treble settings on the transmit audio. The 756 allows adjustment from -12 dB to +12 dB in steps of 2 dB. The PRO settings go from -5 dB to +5 dB in steps of 1 dB. On the air testing suggests that PRO range is indeed limited, and does not provide significant changes.
The PRO features three different transmit audio bandwidths (on SSB). The bandwidths are fixed, and are called narrow (2.0 KHz), middle (2.6 KHz), and wide (2.9 KHz).
The width does indeed change, and is clearly detectable both by another station, and in the audio monitor. Note that the transmit audio bandwidth is independent of the receive audio bandwidth. NOTE: In January of 2002, I learned that some amateurs had discovered that models of the 756 past a certain serial number were built with a normal/wide transmit audio bandwidth switch. The serial number of the change appears to be around 3,000. The switch is totally undocumented, and is located within the radio.
The switch, S801, is on the bottom of the radio. I do not know where it is located. The swiched is marked N (normal) and W (wide). By default, it should be in the N position. If you move the switch to the other position, your transmit audio bandwidth will become wider. When the first rumors of the PRO broke, I was hoping that ICOM would add IF DSP to the 756, while keeping the existing 756 IFs and filter arrangement - perhaps with a few more filter slots. The PRO implements a different set of IFs, with the DSP at the last stage before conversion to audio.
The DSP is responsible for almost all of the receiver selectivity. In the end, DSP still does not seem completely up to the task, although it is getting very close. It's hard not to compare the 756 and the PRO against the Yaesu FT-1000MP, and the new Mark V. The Yaesu radios are known for their immunity against interference from strong signals near the desired frequency. Still, the DSP implementation in the Yaesu radios, in my opinion, is very primitive. What I would really like to see is a quad conversion receiver with a Yaesu front end, complete with extensive filter options at 2 IF stages.
The final IF stage would be the PRO implementation. For me, this would be an irresistible combination.
The early IF stages would establish the approximate desired bandwidth, and the final IF DSP would realize the exact desired bandwidth. The ultimate startup guide pdf. update, June 2002: The TenTec Orion appears to take this approach, and is a blend of the strengths of the Yaesu and ICOM radios, while attempting to fix all of the problems.
If it can perform up to expectations, it should be a very fine radio. 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 available. In visiting the excellent web site of, I discovered a link to an. The manual may also be downloaded from the This web site contained an on-line copy of the PRO II user's manual, which apparently was submitted to the FCC as part of the approval process.
I downloaded the manual, and compared it, page by page, to my PRO manual. While I make no claims that I discovered every difference, those that I did find are listed in the following paragraphs. By early 2003, ICOM made available many of its manuals on.
Click on Download. 1. In general, the time that you have to hold in a button to activate an alternate function has been reduced from 2 seconds to 1 second. This appears to apply across the board.
The front panel Bk-In Delay and Key Speed knobs have been swapped. The Speech button has been turned into the Rec/Play button for Audio Recorder Channel R4. The Lock button has been turned into the Lock/Speech button.
To activate the 'old' Speech function, press the button for 1 second. The Screen Menu Arrangement is changed. When completely backed out of all levels of menus, the 'soft' buttons are now labeled: Scope, Voice, Keyer, Memory, and Scan, as opposed to Scope, Voice, Memory, Scan, and Set. New Noise Blanker level set mode.
Adjust the value from 0 to 100 percent. New DSP Filter Shape set mode. Select Soft or Sharp for CW and SSB. New Preamp explanation section. DVR Explanation improved.
90 total seconds of XMIT audio capture possible. One-touch voice record and playback described.
Reference to IC-PW1, IC-4KL, IC-2KL/IC-AT500 in the original PRO manual replaced with just a reference to the IC-PW in the PRO2. Display Type. There are now 8 display types, as opposed to 4 in the PRO. DSP Filter Set Mode described. Soft/Sharp selections.
Quick Rit/ DTX Clear set mode described. SSB/CW Synchronous Tuning set mode described.
Claims to keep the signal tuned in, even when going from SSB to CW. The frequency may be automatically shifted. CW Normal Side Mode added. Selects the carrier point of CW mode from LSB and USB. External DVR (digital voice recorder) triggering interface schematic presented. Uses pin 3 from the front panel microphone connector.
By using up to 4 switches, and some resistors, you can trigger any of the recorder channels, or the CW memories (if in CW). CI-V radio address (default) is 64h on the PRO2 and 5Ch on the PRO. General frequency coverage now specified by country. 5 countries specified.
Comments I composed the following comments for the ICOM reflector No new controls or connectors were added to the case. I am talking about physical holes. It has already been discovered and reported on this reflector that you can use - on CW, with the existing PRO. As best as I can tell by experimentation, you cannot get at the CW or 'shaper' filter in SSB. I do not know if the 'soft' and 'sharp' filter shapes in the PRO2 are something new and different.
Cara mengaktifkan windows 7. If they are not, then there is no net improvement for CW, and the only change is that you can now listen to SSB with the 'sharp' CW filter shape. I wonder if that's useful?
I felt that the PRO digital voice recorder was nearly useless due to the user interface. The PRO2 is much better, what with the dedicated front panel button, and the ability to connect a simple external switch to trigger playback. That same switch works with the CW memory keyer too, which is a definite enhancement. Still, you cannot trigger the recorder from the computer interface, which would make it possible to run the radio completely from the computer keyboard, which is often very nice in contest situations. For me, the possible added value of the PRO2 comes down to the receiver changes. Until somebody can do a side-by-side comparison, it's all guessing. My only fear is that ICOM made changes that impact measurement numbers, but did not really improve the receiver.
Many folks really follow the numbers in the various popular reviews, and take them as an absolute ranking of the current crop of radios (usually to justify their purchase decision). A few dB will change certain rankings, but might not be audible. I hope that the changes do make a (useful) difference. Anybody directly comparing the PRO2 to a PRO should also see if the new 'soft/sharp' CW filter shapes are what already exists on the PRO.
My guess is that they are the same, meaning that all that has been added is the ability to listen to SSB with the 'sharp' filter shape. It remains to be seen if that is a good thing. Last update: Wednesday, February 26, 2003 05:59:55 PM.
Adam, VA7OJ/AB4OJ's IC-756Pro III User Review Adam, VA7OJ/AB4OJ's IC-756Pro III User Review Initial observations (July 2005) On June 30, I picked up my new IC-756Pro3 (S/N 32025XX) at a local dealer. That evening, I installed the Pro3 in my station. Preliminary findings are that it pulls weak, noisy signals out of the noise somewhat better than the Pro2. I was able to work a number of SSB stations on 40m which I would not have heard on the Pro2. The NR and NB appear to have been significantly improved. Overall, I would judge that the S/N ratio is better than on the Pro2, even in the presence of power-line noise. I find myself routinely operating with the preamp off; on the Pro2, I invariably had Preamp 1 on.
The next day, I was able to sustain the sked with my friend Matt KK5DR somewhat longer, as the Pro3 'hears' signals buried in the noise somewhat better than the Pro2 did. I am able (by using a combination of NR, NB, Twin PBT and Manual Notch) to squeeze intelligible copy out of the assorted 'garbage' on the band more effectively than on the Pro2. In addition, the Pro3's strong-signal behaviour appeared to be excellent. S9 + 60 dB signals 1 to 2 kHz above and below our channel edges did not produce any perceptible artefacts in the received audio. When switched in, Preamps 1 and 2 do not raise the audible noise level in the receiver as much as they did in the Pro2.
In the Pro3, the preamps have been designed for highly linear large-signal handling, consistent with a low noise figure. Preamp 1 has negative feedback to improve linearity without compromising NF. There has also been a significant gain redistribution. The first mixer has lower gain, with the result that the scope module in the Pro3 has its own to bring up the vertical sensitivity of the scope.
Notes on ALC The ALC is a little less sensitive; I need to set the Quadra ALC menu to 5 bars for 1kW output, vs. 4 bars for the Pro2.
As is the case for all other Icom HF transceivers, the rear-panel ALC jack is compatible with a negative-going ALC voltage in the range 0 to -4V. Should never be applied to the ALC jack. In August 2007, I performed an ALC overshoot test on my Pro3/Quadra station. Is the test report. There have been some improvements in operational convenience.
The mini-scope is great - you can now display 3 windows; frequency/mode etc., mini-scope and bar-graph meter, filter menu or any other lower window that used to suppress the scope on the Pro2. There are two clock displays - UTC and local - and a simple screen-saver which displays the owner's callsign moving about on a black background. By being able to leave the bar-graph meter on-screen along with the scope, I learned that compression peaks at 6 to 7 dB when it only shows 2 to 3 dB on the much slower moving-coil meter. Display quality I have the impression that the Pro3's TFT display is superior to that of the Pro2. The screen image is brighter and a little sharper, the contrast is much better and the colours are more saturated. As the ARRL, RSGB and others have already subjected the Pro3 to exhaustive test suites, I felt that any such effort on my part would be redundant (apart from the fact that my second signal generator is much too 'dirty' for meaningful RF 2-tone measurements!) To satisfy my own curiosity, though, I ran a few quick receiver tests: MDS, reciprocal mixing noise and filter shape factors. The test setup was as follows: HP8640B signal generator, calibrated against R&S URV4-03 RF power meter with 0 dB probe; Sinadder 3 configured as true RMS audio voltmeter connected to SPKR jack.
NB off, NR off, ATT = 0 dB, AGC MID. Offset tone pitch = 1 kHz (SSB), 600 Hz (CW). SSB and CW 'Sharp' filter shapes selected. 1: MDS (Minimum Discernible Signal).
In this test, MDS is defined as the RF input power which yields 3 dB unweighted S/N at the output. The results obtained are very close to those in. Table 1: MDS (Min. Discernible Signal) MDS at 14.1 MHz (dBm) Preamp SSB 2.4 kHz CW 500 Hz BPF Off -126 -131 1 -133 -139 2 -135.5 -142 2: Reciprocal Mixing Noise. Occurs in a superheterodyne receiver when the noise sidebands of the local oscillator (LO) mix with strong signals close in frequency to the wanted signal, producing unwanted noise products at the intermediate frequency and degrading the receiver sensitivity. Reciprocal mixing noise is a measure of LO spectral purity.
In this test, a strong 'undesired' signal is injected into the receiver's RF input at a fixed offset from the operating frequency. The RF input power is increased until the receiver noise floor increases by 3 dB.
The reciprocal mixing noise parameter, expressed as a figure of merit, is the difference between this RF input power and measured MDS. The test is run with the 2.4 kHz SSB filter selected, and preamp off. The higher the value, the better. Table 2: Reciprocal Mixing Noise Recip. Mixing (dB) Offset kHz 3.6 MHz LSB 14.1 MHz USB 2 80.5 79 3 83.5 81 5 88 86 10 95.3 91.5 3. DSP-IF filter shape factors.
A quick check of -6/-60 dB shape factors was performed for the 2.4 kHz SSB, 500 Hz CW and 250 Hz CW IF filter settings. ( Note: was on for CW filters.) Shape factors for all 3 filter settings met or exceeded Icom's advertised specifications. The measured -6/-60 dB shape factor for the 2.4 kHz SSB filter was 1.24; the spec is 1.5. Tip: To achieve optimum S/N ratio, the selected IF-filter bandwidth should not exceed the occupied bandwidth of the received signal. SOFT SSB filter roll-off. Test conditions: 10.000 MHz LSB, 2.4 kHz filter selected, RF input power -103 dBm (below AGC threshold), AGC off, preamp off, ATT = 0, NR off, NB off, Twin PBT neutral. Table 3 shows the roll-off for the SHARP and SOFT filter settings.
Table 3: SSB Filter Roll-off Offset Hz SHARP dBr SOFT dBr 250 -4 -8 300 0 -5.5 400 0 -4 500 0 -3 750 0 -1 1000 0 0 2000 -2 -2 2500 -3 -7 5. NR noise reduction, measured as SINAD. This test was intended to measure noise reduction on SSB signals close to the noise level. Initial test conditions: Sinadder configured for SINAD measurement. 10.000 MHz LSB, 2.4 kHz filter selected, AGC MID, preamp off, ATT = 0, NR off, NB off, Twin PBT neutral. The receive frequency was offset +1 kHz to produce the test tone, and RF input power was adjusted for a 6 dB SINAD reading (-127 dBm).
NR was turned on, and SINAD read at 30% and 50% (max.) NR settings. The results are given in Table 4. Table 4: NR vs. SINAD NR setting% SINAD dB 0 6 30 12 50 (max.) 14 This shows an S/N improvement of 8 dB with NR at maximum for an SSB signal roughly 6 dB above noise level.
This is an approximate measurement, as the amount of noise reduction is dependent on the original signal-to-noise ratio. As in the IC-7800, the upper and lower -6 dB points of the transmitter audio-frequency response are independently. This capability, along with the bass and treble menu, offers many intriguing possibilities. Thus far, I have been using default settings, but plan to do more experimentation. of the IC-756Pro2/3 Mic Equaliser The QSK 'dit-clipping' issue As discussed in the ARRL Test Report, CW operators will be very relieved to hear that the 'dit-clipping' problem which plagued the 756Pro2 in full-break-in mode has been completely eliminated from the 756Pro3. A quick check has confirmed this.
It has been reported that the Pro2 NR's heuristic correlation-discrimination process (correlated signals vs. Non-correlated noise) becomes 'acclimatised' to the prevailing SNR and becomes less effective over time. Keying the transmitter reinitialises the NR process, creating a perception of improved NR efficacy. George W5YR has contributed an on this topic to my IC-756Pro/Pro2 User Review. I have a sneaking suspicion that the NR process in the Pro3 reinitialises itself automatically every 15 sec.
This, added to the improvements in the receiver's RF chain, may explain the improvement in weak-signal handling with NR on (as noted above.), Section 5-2-1, describes NR in greater detail. More on NR: Normally, I leave the NR control at 50 to 60% in SSB mode, with AGC = MID. It knocks down the band noise by about 20 dB, but does cut the treble response somewhat as is to be expected. It increases the S/N ratio of the received signal noticeably, and very often makes the difference between copying and not copying a weak SSB signal. There is a slight, but perceptible decrease in noise level between 50% and 60%. Increasing the setting above 60% does not reduce the noise level further, but does not cause distortion.
(In the 756Pro2, 50% was the limit of noise reduction.) In CW mode, the NR will be less effective, as the noise bandwidth is much less than in SSB, and the NR algorithm has less noise power to work with. I find that with NR at 50%, there is a noticeable noise reduction with the 1.2 kHz filter, less with the 500 Hz filter and none to speak of with the 250 Hz filter. Again, this is to be expected (N = kTB). During the test I conducted, I selected AGC = FAST.
I did not observe distortion of the CW signal at any NR setting, even with the IF bandwidth reduced to 50 Hz via Twin PBT. (At the time, I was listening to CW signals varying in level between S0 and S5.) When I operate CW, the NR control stays at 50%.
The noise reduction obtained with BW = 500 Hz and above is still useful. The received audio in CW mode is much more pleasant to listen to, and less fatiguing, than on the 756Pro2 or 756Pro. This is particularly noticeable when using the narrow IF filters (500 Hz and less). The 'background' is much quieter, and the effect previously reported in the 756Pro and 756Pro2 (especially with CW Pitch. Table 5: IC-756Pro3 Settings for Heil Elements Heil Element Mic Gain TBW COMP. Bass EQ dB Treble EQ dB HC-5 12 o'clock MID 12 o'clock -2 +3 HC-4 1 o'clock NAR 1 o'clock -2 +5 Wide Range 10 o'clock WIDE 9 o'clock -3 +5 PR-781 10 o'clock WIDE 9 o'clock +1 +3 PR-781 'DX' 10 o'clock MID 11 o'clock -1 +3 Electret 9 o'clock MID 9 o'clock -3 +3.Set COMP for 6 dB on voice peaks (on bar-graph meter). The IC-756Pro3 transmitter offers a of bass/treble and AF response adjustment (selectable low and high -6 dB points.) With this much flexibility, it should be possible to configure the radio to work well with almost any microphone.
Given the communications mission referred to above, though, the best choice will always be a microphone optimised for radiotelephone communications, as opposed to a microphone more suited to broadcast or recording applications. Output Transducers (Headphones and Speakers) The same general considerations apply to output transducers as to microphones.
The amplitude/frequency response of a headset or speaker intended for radio communications should closely match that of the receiver to which it is connected. If the receiver is 6 dB down at 200 Hz and 2.7 kHz, the transducer's -6 dB points should be in the same range. The use of a 'wide-range' transducer with a -6 dB response of 50 Hz - 18 kHz can actually be counter-productive, as it can pass mains hum at the low end and white noise (hiss) at the high end. These unwanted sounds can actually degrade articulation when listening to weak and/or noisy signals. Headphone Level In the IC-756Pro3, there are 180Ω resistors in series with the tip & ring leads of the front-panel PHONES jack (one resistor in each lead). (More information ).
Spectrum Scope Vertical Sensitivity (August 2005) With Preamp 2 enabled, 0 dB attenuation (RF and scope) and autotuner disengaged, the Pro III spectrum scope will display a visible spike with 0.06 µV (-131 dBm) at the antenna socket. (This was measured at 14.1 MHz with the HP8640B signal generator, calibrated against the R&S URV4-03 RF power meter with 0 dB probe.) The radio was also in CW mode, with the 500 Hz filter selected. The corresponding figure for the was 0.12 µV (-125 dBm). The Pro III, like its predecessors, has a resolution bandwidth (RBW) of 1 kHz at -6 dB. A typical scope screen.
I have noticed a slight interaction between Spectrum Scope vertical amplitude and Dual Watch BAL control setting on the IC-756Pro3. Dual Watch was enabled, with 14316 kHz on MAIN, and 14186 kHz on SUB. When I rotated the BAL control fully clockwise to cut off the Main channel, I observed that the scope grass level rose approx. Per the block diagram, the scope pickoff point is at the output of the MAIN (A) 1st mixer, which also feeds the MAIN Balance PIN attenuator.
I believe that the following is occurring: When the PIN attenuator is completely cut off, it breaks the signal path to the next stage (the IF preamplifier feeding the 1st IF combiner). This partially unterminates the MAIN 1st mixer output, causing the RF voltage at that point (and consequently at the input to the scope RF amplifier) to rise by about 6 dB. There is no other apparent change in receiver behaviour (e.g. Instability etc.) Comparing the 756Pro3 to the 756Pro and 756Pro2 yielded these results:. Pro - scope falls with BAL at 100%. Pro2 - no effect (scope fell 3 dB with BAL at 100% in one sample). Pro3 - scope rises 6 dB with BAL at 100%.
Note: Several units of each model type were checked. This is what I believe is happening: The Pro 1st mixer is followed by an LPF. When the PIN diode attenuator is cut off, the LPF is mis-terminated (looks into an open.) This apparently reflects a lower impedance back towards the 1st mixer, loading it down and reducing the signal amplitude at the scope input.
In the Pro2, there is no LPF following the 1st mixer. The mixer output is fairly low-Z, so the mis-termination when the PIN diode attenuator is cut off will not cause much change in signal level at the scope pickoff point. In the Pro3, the 1st mixer has a lower IF output than in the Pro or Pro2 (hence the need for an in the Pro3 scope input line). It is likely that the 1st mixer output is noise-matched to the PIN attenuator, in which case it will have a higher source impedance to match the load conjugately. The rise in load impedance when the attenuator goes to cut-off will cause approx.
6 dB increase in output voltage. The scope input voltage will rise by the same amount. This is surmise on my part; I have not opened up the radio to take measurements. This phenomenon is interesting, but not a major issue as it does not affect receiver performance at all. In practice, with Dual Watch on, the BAL control is normally set between 40 and 60%, and the interaction does not occur. Comment on the IC-756Pro3 Autotuner (December 2005) Matt KK5DR has found that the IC-756Pro3 autotuner tunes a little faster than that of the IC-756Pro2.
A quick check on my Pro3 confirmed this. There has been no change from the IC-756Pro2 in this area. Please refer to the following links:. Q: Does the IC-756Pro3 have a synchronous AM detector? A: None of the Icom DSP-based HF transceivers has an AM synchronous detector in the sense of a phase-lock demodulator which regenerates the incident carrier, demodulates the sidebands against the local carrier and 'votes' the sideband with the best S/N ratio.
All the Icom DSP-based radios (including the IC-746Pro, the IC-7800, the IC-756Pro series and the IC-7000) employ the same DSP algorithm. This models a phasing-type modulator and demodulator for SSB and AM. The difference between SSB and AM is that in SSB, the unwanted sideband is cancelled, whereas in AM the upper and lower sidebands are added in phase to produce the composite baseband. Unlike a true synchronous detector, the AM demodulation process in the Icom DSP design does not 'vote' the sideband with the best S/N ratio. AM broadcast reception is very effective on the IC-756Pro series, but is subject to selective fading. One can use ECSS (by receiving AM in SSB mode) to reduce this, and select the quieter sideband manually. Q: Can you explain the amplitude-sensitive digital artefacts which appear on the transmitted AM signal?
A: With any system involving A/D and D/A conversion, quantizing distortion will occur at high signal levels. This will manifest itself as noise on modulation peaks.
As the ADC and DAC used in the Icom radios are 24-bit devices originally intended for high-grade audio applications, quantizing distortion will be insignificant as long as the devices are not overdriven. Note that as the analogue input level to the ADC approaches the 'all 1's' point, quantizing distortion will increase sharply. If MIC GAIN is set for 90% modulation, using the Spectrum Scope as described, the ADC will remain well within its linear range. Also as discussed above, P o must not exceed 25W resting carrier. The spectrum-analysis test (described ) yielded a clean display, without visible artefacts. In January 2007, I ran an AM listening test on my IC-756Pro3 at 25W resting carrier and 90% modulation, using a simple tuneable demodulator consisting of a military ME-61/GRC field-strength meter connected to a good-quality headset. The recovered audio sounded smooth and clean, without audible artefacts.
This tended to confirm the spectrum-analysis test. The RX-ANT input socket is intended for the connection of a separate receiving antenna such as a Beverage, loop or long-wire. Such antennas, if co-sited with the transmitting antenna, can induce extremely high voltages at the RX-ANT input during transmission. This is particularly true on 160m and 80m. Recently, damage to the front end of an IC-756Pro2 fed from a Beverage was reported on some forums. On researching this topic a little further, I noted that the 756Pro and 756Pro2 RF Unit boards have a varistor (R111) to absorb excess RF voltage, and a fuse bulb (DS111) in the RF signal path from the RX-ANT jack to the ANT/ANT-R selection relay (RL101).
Excessive RF power applied to the RX-ANT jack will blow DS111. On the 756Pro3 RF-B Unit board, varistor R101 is still seen, but DS111 has been omitted. Interestingly enough, though, the 756Pro3 RX-ANT circuit incorporates an RF sensor (D101, Q103, Q104) which operates the selection relay (RL-101) when RF is applied to the RX-ANT socket, thereby breaking the RX-ANT signal path.
This feature is lacking in the 756Pro2. View of the IC-756Pro3, IC-756Pro2 and IC-7800 RX-ANT input circuits. It is strongly recommended that an external protective relay circuit such as the be connected between the receive antenna feedline and the RX-ANT input.
Q: Are the ANT1 and ANT2 inputs both grounded when power is off? A: No, this is not the case. If we follow the RF signal path on the CTRL-A Unit from ANT1 and ANT2 to the RFRX input (RF-B Unit), we see that when RL1, RL2, RL3 and RL4 are released, the signal from ANT1 is routed via RL3/1 NC, RL2 NC, RL1 NC, RL4 NC. L27 and L28 to J2 (RFRX). ANT2 is earthed to chassis via RL3/2 NC. (IC-756Pro3 Service Manual, p.
All relays are released when power is off. When I turn on the Calibration Marker, the S-meter reads S9 + 14dB with the antenna disconnected and S9 + 11dB with the 40m antenna connected. Does this 3 dB difference mean that half the Marker power is going out the antenna? Also, can I use the Marker to check S-meter calibration? The marker amplitude as displayed on the spectrum scope will vary slightly between individual radios.
One can use it as a rough check to see if the S-meter is reading correctly. The marker signal is applied at the of the splitter which feeds the incoming RF signal to the Main and Sub 1st mixers. The load impedance presented to the marker source changes slightly if the antenna is connected with no preamp in the signal path; this may account for the drop in amplitude with the antenna connected. With Preamp 1 or 2 selected, there is no change, as the preamp buffers the marker injection point from the antenna input. I measured the marker signal leakage from the antenna socket with a Millivac MV-723B broadband RF millivoltmeter terminated in 50Ω. The leakage is negligible with either preamp in-line.
With preamp off, marker on and f = 7.4 MHz, I read -48 dBm at ANT2. The readings at 3.0 and 30.0 MHz were both -52 dBm. This is the composite signal power of all the 100 kHz harmonic spikes passing through the BPF for the selected frequency range.
( Note: The test frequency was just outside the 40m amateur band, to prevent damage to the meter's sensor in the event of accidental keying.) If you are concerned about this leakage, you can enable Preamp 1 or 2 whilst the marker is on. In response to an enquiry, I measured CW rise-times on my IC-756Pro3 using a Tektronix 455 oscilloscope connected to a line sampler placed between the ANT2 socket and a 50Ω termination. Test Conditions: f = 14050 kHz. Time-base set to 1 mS/div. Note: Rise-time is defined as the time to go from zero to 100% P o. 6 vertical divisions = 100% P o (p-p). The test results are listed in Table 6.
The test screenshots can be seen. Table 6: Rise Time CW Rise Time mS Nominal Measured 2 1.5 4 3 6 5 8 6 The rear-panel XVERT RCA jack is bidirectional. In response to a reflector request, I measured the transverter RF drive level (in transmit) on my IC-756Pro III. Here are the data: Test Setup: IC-756Pro III, S/N 32025XX, with XVERT jack connected via coax jumper to 50Ω terminated probe of Millivac MV-723B RF Millivoltmeter.
(IC-756Pro III User Manual, p. 7-pin DIN plug with Pins 6 (XVRT) and 7 (+12V) bridged via 27KΩ 0.25W resistor, plugged into Pro III ACC (2) socket to activate XVERT mode.
Pro III set to 28100.000 kHz, RTTY mode. Table 7: Transverter drive levels, key down RF Power Setting XVERT Output, dBm Minimum -21.0 50% -8.8 Maximum -2.0 In receive, the signal applied to the XVERT jack is routed to the RF BPF input. The transverter IF output power at this point should not exceed approx. The ALC RCA jack is active in XVERT mode.
A transverter equipped with a negative-going ALC line (0 to -4V DC output) will be compatible with the exciter's ALC jack. There have been reports of low SSB power output in the IC-756Pro3. It has been found that all too often, these are the result of incorrect measurement methods, inaccurate test equipment and/or low DC primary supply voltage.
The following RF output test procedure should yield reliable results:. Measure the power output in CW, FM or RTTY mode with RF Power fully clockwise, and your power meter terminated in a good-quality 50-ohm resistive load. A calibrated Bird 43 or equivalent average-reading meter accurate to within 5% is recommended. Using an accurate DVM, check the primary DC voltage at the rear-panel power socket with the radio delivering maximum output. At 13.8V DC, the transmitter should deliver 100W or more to the load. Run the SSB PEP test described. An oscilloscope is required for this test.
If the displayed envelope amplitude on voice peaks is equal to the carrier amplitude in RTTY mode for 100W output, the Pro3 PEP output is 100W. Note: If the CW output measured in Step 1 is significantly less than 100W with 13.8V primary DC input, or if PEP output measured in Step 3 is significantly below 100W, the radio may require realignment or repair.
If the radio is still under warranty, or if you do not have access to the test equipment specified in the service manual, do not attempt any alignment procedures. The radio should be sent in to an authorised Icom service centre. Mitsubishi, the manufacturer of the 2SC5125 used in the 756Pro series PA Unit, have recently discontinued all their RF power BJT lines. This event has forced Icom to design a new PA Unit based on MOSFETs. To the best of my knowledge, the new PA is showing up in US/Canada Pro3's (#32 variant). with S/N 32045XX and higher. The MOSFETs are also Mitsubishi parts.
The original PA Unit uses BJT's, not FET's (2SC1971 pre-driver, 2 X 2SC1972 driver, 2 X 2SC5125 PA.) The line-up in the new PA Unit is as follows: 2SC1971 (BJT) pre-driver, 2 X RD15HFV1 (MOSFET) driver, 2 X RD100HHF (MOSFET) PA. The HF/6m PA in the IC-7000 also uses a pair of RD100HHF's. A typical MOSFET circuit will have 13 dB power gain vs. 10 dB for a BJT circuit. This reduces the required drive power by 50%, i.e.
5W vs.10W drive for 100W output. This will reduce the driver stage's IMD contribution. The MOSFET PA already has slightly lower IMD (perhaps 1 or 2 dB), so the transmitter will be cleaner overall. Owners of IC-756Pro3's with the earlier PA Unit need not be overly concerned. The 2SC5125 is a very tough device, and should last for many years with reasonable care. The Toshiba 2SC2782 is a sub for the 2SC5125, and is available from singly and in matched pairs. Furthermore, I am confident that Icom laid on an adequate stock of BJT parts at their service centres to maintain the existing installed base when Mitsubishi advised them of the impending discontinuance.
It should be noted that the IC-706 MkIIG went through a similar exercise a few years ago when Motorola discontinued the PA devices. Greg Buhyoff K2UM kindly provided a partial and of the new PA Unit (originals courtesy Icom Inc.) I am also indebted to Greg for supplying of the new PA Unit. Other regional variants will have different serial number ranges for the change-over to a MOSFET PA. Note: Rumours that Icom redesigned the PA Unit in response to 'PA failures' or 'low output' are patently untrue. Q: On my IC-756 Pro III, I am trying to understand how to get rid of that awful crackling and popping sound I hear when on CW mode. This is the only mode on which I hear it; it is really distinct and repeatable when I rotate the CW pitch control, and is most prevalent on 30 and 40 metres. A: Here are some items to check:.: 250Hz 'BPF' filter via menu or a 'non-BPF' 500Hz filter set up via Twin PBT?
(Less ringing for 'non-BPF'.). CW shape factor (in Others/DSP menu): Sharp or Soft? (Less ringing with 'Soft'.). NB settings: How much NB is needed? Is NB threshold too high ( 75%), causing distortion?. Antennas in use: Beverage on RX-ANT input or TX/RX antenna?
If a Beverage antenna is in use, there could be induced voltages on the antenna requiring bleed-off. AGC: Does the crackling and popping exist with the AGC turned off? If yes, turn off pre-amps and attenuate the signal. In general, it is wise to avoid turning the AGC off, to prevent ADC over-ranging which will cause severe distortion. On 40m and below, the ' technique is effective in reducing the noise level.
Test without antenna: Does the static and popping occur without an antenna? If so, it is internally generated, and could indicate a faulty DSP Unit. By Matt, KK5DR. It has been observed that the screen-saver never appears if a mono plug is inserted in the front-panel ELEC-KEY jack. This is normal. The ELEC-KEY jack has tip and ring leads.
Even if Keyer Type is set to Straight in the KEYER menu, the radio's CPU still senses both leads. Although a ground on the ring lead will not key the transmitter, it still acts as an external event or 'stimulus' which will clear the screen saver. If a mono plug is inserted, the plug shell will ground the ring lead, thus clearing the screen saver. For this reason, a stereo plug should always be plugged into the ELEC-KEY jack - even when using a straight key or external keyer.
The rear-panel KEY jack will accept a stereo or mono plug. Every few months, a discussion of 'IC-756Pro3 heat issues' pops up on the forums. In fact, there is nothing to be concerned about.
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The Pro3 does not overheat - as long as it is installed with adequate clear space around it to allow sufficient air-flow for cooling. At least 4' (10cm) of clear space around the top case cover and the rear panel are recommended. The front feet should also be extended. The vent slots in the case and rear panel must be unobstructed at all times. If the Pro3 is correctly installed to allow sufficient air-flow, no additional external fans should be necessary. This has been my experience with the entire IC-756 series since 1998. To my knowledge, there have been no reported instances of Pro3 failures due to overheating.
It should be noted that direct attachment of small muffin fans to the case vent slots of the Pro3 can be counter-productive. Should these fans fail for any reason, they will obstruct the radio's air-flow with resultant overheating. Read the caution on page ii of the Pro3 User Manual.