ICOM IC-R7100 - Squelch opens during scanning when mode is switching to SSB?

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CrazyFin

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I have recently purchased an ICOM IC-R7100 scanner/receiver in excellent condition.
Initial checks with my test equipment indicates that it seems to be in good tune-up.

I have previously owned and tested IC-R9000, IC-R8500 and IC-PCR1500.

This IC-R7100 is nice but I have experienced a minor issue during memory scanning.

I know about R7100 having a noise squelch (that works only for FM and AM) and a S-meter squelch (that works in all modes).

I select an USB or LSB memory channel and set the squelch to a level that precisely closes the receiver and then check that RX is still silent when moving to a memory channel with FM and AM mode.

When I start the memory scan the R7100 always stops temporarily when it goes from a memory channel with either AM or FM mode to a channel with either USB or LSB. It does not happen when going from USB/LSB to AM/FM channels. If I do memory switching manually I can trigger squelch opening by doing the same, i.e. going from AM/FM to SSB and not from SSB to AM/FM.

I can see the S-meter jump slightly when going from a memory channel with AM/FM to a memory channel with SSB so I guess it has to something to do when mode switching from AM/FM to SSB.

This issues causes me to set the squelch to a higher level than necessary causing me to miss low level signals during scan.

I have not seen this issue with other ICOM receivers so I guess this is a design issue with the R7100?

I have read through the service manual trying to understand what causes these issues but it is somewhat above my knowledge level... Page 3-8 in the service manual, paragraph 3-1-20 and 3-1-21.
 

k1xd

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I setup my R7100 receiver as you described. I have several AM-W channels programmed (aircraft). I added an SSB channel and an FM-N channel. I then setup SCAN and mode MEMO (all channels). It works for me.. no pauses. What I do notice is that for the scan to work with the SSB channel, the squelch has to be set at about 1 o'clock on the squelch control and without the SSB channel, the squelch is about 9 o'clock. I believe the SSB mode is an RF squelch and the FM or AM mode is a noise squelch, hence the difference in squelch position.

Dave
k1xd
 

CrazyFin

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Yes, that is correct. I have to set the squelch to approx 0130-0200 (signal meter at approx S7) in order for the scanning to not stop when going from a channel with AM or FM mode to a channel with SSB mode.

The S-meter squelch starts at approx 12 o´clock and up until that level the squelch works as a noise squelch which only works for AM and FM. This means that as soon as one wants to memory channels that has SSB one has to set the squelch past 12 o'clock.

However, if you go to a memory channel with SSB and then set the squelch juuuuust above the level where RX gets silent and then start the memory scan, I guess you will also see a short pause every time your memory scan goes from an AM/FM channel to the SSB channel.
The squelch opens just for like a half of a second but it is still annoying since the scan pauses when going from an AM/FM channel to a SSB channel.
If I scan ONLY SSB channels then I can keep the squelch at its lowest possible setting to the right of 12 o'clock.

So the main problem is that I have to set the squelch so high (based on the current noise level on a SSB channel) that the scan misses lower level signals that would normally open the squelch if I kept it at the lowest level that triggers the squelch open. So instead of having the squelch at for example 1 o'clock when scanning only SSB channels I have to increase the squelch to like 2 o'clock when scanning a combination of SSB and AM/FM channels.
 

Ubbe

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If it still happens with coax removed, there must be a potentiometer to adjust to balance between the noise and signal squelch.

But if it works ok without coax connected it is probably a high noise floor that triggers the signal squelch too early but you could probably use that potentiometer to compensate for that as well, if the noise floor keeps a constant level. Have you tried less amplification or to add attenuation to lower the noise floor?

/Ubbe
 

CrazyFin

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If it still happens with coax removed, there must be a potentiometer to adjust to balance between the noise and signal squelch.
Nope, with coax removed there is no such problem.

But if it works ok without coax connected it is probably a high noise floor that triggers the signal squelch too early but you could probably use that potentiometer to compensate for that as well, if the noise floor keeps a constant level. Have you tried less amplification or to add attenuation to lower the noise floor?
Well, as I have written above it only happens when moving FROM an AM/FM channel to an SSB channel.
It does not happen when moving FROM an SSB channel to an AM/FM channel.

If I for example, while being on a SSB channel, set the S-meter squelch to S5 level (approx 1 o'clock on the squelch) and then move to an AM/FM channel the squelch does not open nor does the S-meter jump.

However, if I now move from an AM/FM channel to the SSB channel the S-meter makes a quick jump from the S5 level (that is the set squelch S-level) up to approx S7 which causes the squelch to very temporarily to open (for about 100-500 ms) and then close again.

I can see the same S-meter jump when moving from an AM channel to a FM channel BUT that does not open the squelch. It only happens when going from AM or FM to an SSB channel and not going from SSB to AM/FM...

Something to do with how the AGC circuit for SSB is being kicked in when going from AM/FM to SSB I guess?
 

CrazyFin

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I have uploaded a "short" video where I am switching back and forth from AM/FM/SSB memory channels and you can clearly see in this video that this very short and quick squelch opening only happens when going from either FM or AM to SSB mode channels and not the other way around.
You can also see the S-meter making a jump when going from FM to SSB channel.
You can also see the same and BIGGER S-meter jump when going from FM to AM but the squelch does NOT open in this case?!

Here is a link to the video on my Google Drive: https://drive.google.com/open?id=0B7z6W_oJVxt3R1NFS1F0TXVwOTA
 

majoco

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I believe that this is done on purpose by the manufacturer. Squelch works with the AGC line which of course is generated by the carrier - but in SSB there is no carrier to stop the scan so it's possible that as soon as there was a gap between words the scan might start again and you would miss the rest until the scan came round again - increasing the scan dwell time solves this problem but of course you do lose a bit of sensitivity.
 

CrazyFin

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Ah ok so it is a design "flaw" or consequence by the design used in IC-R7100?

I do not see this issue with no other of my other ICOM receivers/scanners like the IC-R8500, IC-R9000 or the IC-PCR1500.

I have not seen this issue with my other amateur radio stations with memory scanning functions (Yaesu Ft-1000D, ICOM IC-7300) as well as other more "traditionial" "export" radios like Alan 560, Galaxy Saturn Turbo, CRT Hercule Turbo, Ranger 2995DX as well as many other transceivers.

I have only seen this (so far) with the IC-R7100 and that is why I started to think if it is a tuning/alignment issue or the fact that something is broken in the receiver...
 

k1xd

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The R7100 has two different types of squelch modes, by design. See below. It's a bit confusing. Note that the noise squelch operates only in the AM or FM mode. The threshold squelch operates in all modes and varies squelch based on signal strength. The two modes can't be combined. You use one or the other...

New Picture.jpg
 

CrazyFin

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The R7100 has two different types of squelch modes, by design. See below. It's a bit confusing. Note that the noise squelch operates only in the AM or FM mode. The threshold squelch operates in all modes and varies squelch based on signal strength. The two modes can't be combined. You use one or the other...

View attachment 61523
Thanks kx1d. Howver, if you read my previous posts you would have realized that I am well aware of the two different "squelch modes" that the IC-R7100 has... ;-)

In AM/FM mode the squelch can be used as "noise squelch" while in SSB mode it is used as an "S-Meter"-squelch. S-Meter squelch starts at approximately 12 o'clock poistion.

I also wrote that I am setting the squelch to the 1 o'clock position or even the 2 o'clock position and I still get the problem that when going from an AM/FM mode memory channel to an SSB mode memory channel the squelch opens BUT only temporarily for a few hundred milliseconds (causing the scan to stop).

Please have a look at the video in the link that I posted above and you will realize that this does not seem the be proper behavior by the IC-R7100 (and as I wrote earlier I do not see this "problem" for other ICOM scanners).
I need to dig into the schematics more to understand why this is happening...
 

Ubbe

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It's natural that there is problem with the level squelch when you have a high noise floor and only when you go from a noise squelch channel to a level controlled channel. Why should it also be problem when you leave the problematic level squelch channel and enter noise squelch mode?

You have to look in the schematic for any adjustments of the level squelch or lower the general input signal to the receiver or use a less noisy antenna. A loop antenna have a much less signal than a dipole or longwire, especially if the antenna are not perfect, and the loop are probably more balanced with your current setup and allows you to use a more refined squelch setting.

/Ubbe
 

CrazyFin

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Thanks Ubbe (I see you are located in Sthlm as well. :) ).

I think though that you misunderstand my problem explanation?

I go to the SSB mode memory channel and set the squelch to a proper level to silence the RX.
I then go to a FM or AM mode memory channel (with for example the memory up/down buttons) and verify that RX is still silence and squelch does not open.

If I now jump back to the SSB channel the S-meter BRIEFLY jumps up and squelch BRIEFLY opens up but then immediately closes again (within 100-500 milliseconds).
I can see same S-meter jump when going from a FM mode memory channel and to an AM mode memory channel and in this case the S-meter jumps even more BUT the squelch does not open.

The strange thing is that when going from AM/FM to SSB the squelch opens just shortly and then closes again so the level I have set is correct.

Please look at my video again and you will hopefully see the issue.
https://drive.google.com/file/d/0B7z6W_oJVxt3R1NFS1F0TXVwOTA/view

So it is not the issue of the noise floor in each channel and mode but rather an issue that the S-meter jumps enough to SHORTLY open the squelch. You can see this quite clear in the video that I linked above.
And since the squelch in SSB mode is a signal level squelch the brief and temporary S-meter jump when going to a SSB channel causes the squelch to temporarily open and then immediately close again.

Other receivers I have tested like the IC-R8500 and IC-R9000 does not have this issue.

I have looked in the service manual (for example at http://www.radiomanual.info/schemi/IC-R7100_serv.pdf ). Page 6-8 describes the alignment of the noise squelch and signal level squelch (screenshot attached).

I am not sure that it actually will help but I´ll check the adjustment tonight when back at home.
I still think there is something else not working properly or it is just by design that this brief and strange S-meter jump happens when going from AM/FM to SSB or from FM to AM.
 

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k1xd

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OK..

1. I setup the R7100 with several AM-W frequencies and one SSB frequency.

2. I radiate a signal from the sig gen and adjust level on the SSB frequency so that it's about S5 on the S-Meter.

3. I set the squelch so that the SSB frequency is squelched.. S5 and just a little bit more.

4. Set scan to SCAN and MEMO all channels.

5. YES.. It does exactly what you say. It pauses on the SSB channel.. squelch opens briefly (a few hundred milliseconds?) and then scanning resumes.

6. If squelch is advanced more, to S7 or so, then scan doesn't pause on SSB channel.

Guess this is inherent in the design??

Dave
k1xd
 

CrazyFin

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:)

That is great. I was going to do a similar test tonight at home with my signal generator as well but I am glad that you confirmed having exact same behaviour.

Design flaw I would say...

What frequencies did you test this on?
I have a feeling that this problem is more on HF than on VHF and UHF but I have no proof yet. Will test with signal gen tonight or you can test by scanning memory channels with SSB and FM around 144MHz.
 

k1xd

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AM-W Frequencies were VHF range 119-123 MHZ
SSB Frequency was 27.4 MHZ

Problem could be mode switching, AM-FM to SSB or maybe band switching?

I had a look at the schematic... seems like the place to start would be to look at the AGC line, that's what opens the squelch, and figure out what causes the transient...

That said, most SSB squelch circuits don't work so well unless they are voice detection design.. Signal level SSB squelch design opens on noise, heterodynes, etc...

Dave
k1xd
 

CrazyFin

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@kx1d: Good findings!
Can you please test with setting for example 143.50MHz USB as one memory channel and 144MHz FM as a 2nd memory channel and test again with S5 level on your signal generator.

I am at home now and did an initial quick test by jumping back and forth between those two channels and I can not trigger the S-meter jump in the same way when jumping back and forth between for example 27.555MHZ USB and 27.385MHz FM.

I´ll set up my signal generator in few hours as well to test more thoroughly to verify if this is a problem on lower frequencies only.

I am hoping that someone with good and in-depth knowledge of AGC-circuits work when using signal level squelch.
 

CrazyFin

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Ok I tested with my signal generator now and no matter what frequencies I test with I get the same problem.

1. Store 1 memory channel at 144.25MHz USB and one memory channel at 145MHz FM-N.

2. Set signal generator to for example 144.25MHz and set output level to -86 dBm with no modulation which generates approx S5 in FM Narrow mode on the R7100.

3. I then set the R7100 to USB mode and turn up the squelch so that the RX gets silent. Squelch is then at approx 1 o'clock (S-meter at approx S5.5/S6).

4. Step back to the memory channel at 145MHz that has FM-N as its mode to check that squelch is still closed.

5. Start the memory scan and you will get a BRIEF pause AND a small jump in the S-meter EVERY time the scan comes to the memory channel with 144.25MHz USB. The pause is just about few hundred milliseconds but it causes the squelch to open and pause the scan for the delay time I have set. Very annoying...

6. Try now with setting for example 30% AM modulation with 1250 Hz tone on the carrier signal on 144.25MHz.

7. Start the scan and you will again get the same "error" BUT now you can even hear the tone "squealing" shortly when the scan comes to that channel. Almost like if it tuning quickly (10-100ms) into the correct frequency (like tuning a clarifier knob).

I have attached a screenshot of the Demodulator and AGC circuit block schematic found on page 3-7 in the service manual. Maybe someone can explain why this might be happening?
 

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