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Robin Hou
Joined: 19 Jan 2017
Posts: 15
Location: El Monte, CA
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 Posted: Tue Aug 07, 2018 9:47 am Post subject: Garmin 250XL Squelch Issue |
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I have a Garmin GNC 250XL in my CJ-6. I fly mostly in formation with others. There are 2 CJ's that I fly with which have Icom IC-A200 radio installed in them.
When I fly with Icom IC-A200 equipped plane in formation, the transmission from Icom would trip my 250XL squelch which requires resetting my auto-squelch by pressing SQ button. Sometimes it is so bad that I cannot hear any transmission for the rest of the flight even after I have reset the SQ button multiple times. When the problem occurred, the 250XL continued to transmit fine but I heard no transmission.
I have no problem flying formation with other planes with non-Icom radios; only the Icom radios cause this issue. Also no issue with ATC when I am flying solo. The radio has been bench checked OK.
Any advise on how to pin point the issue is greatly appreciated. Thanks in advance.
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mark.bitterlich(at)navy.m
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| Posted: Tue Aug 07, 2018 10:27 am Post subject: Garmin 250XL Squelch Issue |
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Are you saying that when you fly in formation with aircraft using the IC-A200 radio, that without them ever transmitting to you ... as in they are not talking or pushing the PTT button..... that as soon as you get close to these aircraft that you start to hear static in your radio? You say that the Icom would "trip my 250XL squelch". What exactly does that mean? I grasp what it PROBABLY means, but I need to know precisely what is going on. As I said, do you start to hear static noise in your headset, and that you would try to make it stop by hitting the SQ button? And that even when you got the noise in your headset to stop making noise, you then could not hear anyone else talk? Please verify this as correct.
1. Did you have the flight (as in all aircraft in formation) change to a different frequency and see if it changed what was going on?
2. When it was happening, did you try YOUR radio on a different frequency to see if you could hear anyone else? As in an ASOS transmission, tower, ground, ATC, anyone?
What it sounds like ... without test data.... is that the ICOM radios have Local Oscillator leakage and they are actually radiating enough energy to impact the radio in your aircraft. The only way to know this for sure is to use a SpecAn (Spectrum Analyzer) on the offending aircraft radios (the Icom's) and see what it is for sure. It is important to know that when this happens, do you experience it only when you are on the same frequency that they are on, or can you switch to another frequency (with them staying where they were) and then your radios receiver starts working well again. Then when they switch to your new frequency, that the problem comes back. Further, that when they turn their radios completely OFF, that your receiver start working perfectly again.
There are a few things that can cause this to happen but to narrow them down, you have to be very specific in exactly how this occurs, and then run tests as noted above. It is possible that if you all try a totally new frequency, well removed from the one you have been using, this problem might actually disappear. But ... it also might not... and that is also critical to know.
In the end, you have stumbled on a very rare problem that will more than likely take some local expertise with the right test equipment to solve. If I could get my hands on the offending aircraft, using a SpecAn, we could nail this down very quickly ... but without that, it might prove difficult.
Mark
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Robin Hou
Joined: 19 Jan 2017
Posts: 15
Location: El Monte, CA
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| Posted: Tue Aug 07, 2018 11:28 am Post subject: Re: Garmin 250XL Squelch Issue |
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Hi Mark,
Sorry, I should have been more clear. I say that the Icom would "trip my 250XL squelch"; what I mean is when the Icom transmits, my 250XL auto squelch function would adjust itself to a point that I can no longer hear any transmission from any radio. It occurred mostly when the Icom equipped plane is flying lead which requires transmissions lasting for a 30 seconds or so at a time. When the Icom equipped plane is not lead and stays radio silent, there was no problem. When the Icom equipped plane is not lead and only does very short transmissions (i.e. checking in), there is no problem.
Interestingly, my portable radio, which has manual squelch adjustment, could receive transmission when my 250XL is silent.
You ask 1. Did you have the flight (as in all aircraft in formation) change to a different frequency and see if it changed what was going on? Yes, the issue had occurred on 121.20, 123.30, 135.95 & 135.97.
You ask 2. When it was happening, did you try YOUR radio on a different frequency to see if you could hear anyone else? As in an ASOS transmission, tower, ground, ATC, anyone? Yes, changing frequency on my 250XL does not restore its ability to receive transmission. When the issue occurred in the beginning of a flight, I could resolve the issue by pressing SQ; however, after about 10 to 15 minutes, pressing the SQ does nothing.
Your help is greatly appreciated.
Robin
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mark.bitterlich(at)navy.m
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| Posted: Wed Aug 08, 2018 10:53 am Post subject: Garmin 250XL Squelch Issue |
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Ok, your description is making some assumptions about what is going on, which I'd advise we not do. I'm still less than clear on EXACTLY what is happening, although we are starting to zero in.
So ... are you saying that when the Icom equipped airplane is close to you, and makes a rather long transmission ... something happens. Question: Do you stop hearing him WHILE he is transmitting, in that he is talking, you hear him, then WHILE HE IS TALKING, YOU STOP HEARING HIM? And then you can't hear ANYONE else? Go through this with me again step by step. Or tell me I've got it correct please.
The most important statement you made was that you could press the SQ switch initially and things would work, and then pressing it again later on..... results in nothing being heard on ANY freq.
Let's talk about that SQ button on your radio so you are clear what it actually does. It does not "reset" ANYTHING. It simply turns Squelch OFF. With squelch off, and the volume turned up, you should be able to hear static in your headset. Try this on the ground with the engine not running, before your flight. Just push the SQ once, listen for static, push it again and the static goes away. So it is a SWITCH ... push once, it turns off squelch, push again it turns it back on.
I think you are getting the wrong idea of what "Automatic Squelch" really is. It is not something that is "adjusting itself" in flight. It is in fact nothing more than a comparator circuit which measures signal to noise ratio, and when the signal to noise ratio achieves a PRESET LEVEL, the speaker is turned on. That is ALL that it does. Pushing the SQ switch just turns the speaker on ALL THE TIME and bypasses this circuit. Pushing the SQ button does nothing to "reset" or "readjust" anything. It just bypasses the circuit that turns your speaker on automatically when there is a strong enough signal.
Now that you understand this, a light bulb should be starting to glow a little bit.
The situation is simply this: You are close to an aircraft with a strong transmitter. I don't believe it has anything to do with the other aircraft having an Icom radio, OTHER THAN, it has been my experience that the Icom Radios put out a tad more power than some others, and also they tend to modulate right at 100%, which is actually a good thing. But the point is that YOUR aircraft is in the near field of this transmission, and that means your receiver is being hit with a ton of energy. And ... I don't believe it is handling it too well at all. Meaning, I think that there is a component in your receiver that is being overloaded and then stops functioning. I base this on one very important point:
You say that once it happens, you can push the SQ button one time, and you hear no static, or transmissions from anyone else. We must be clear on the fact that you now understand that the SQ button is a SWITCH. Hit it once, and it turns the speaker on all the time, hit it again and it goes back to allowing the circuit to turn on the speaker. You need to be very clear on this, and listen to it on the ground with the engine not running, so you can fully understand the function.
If you then go flying again consider pushing the SQ one time, and let it run with the speaker on all the time. It is annoying I know, but do it. Then join and tell the guy in lead with the Icom to transmit for 30 seconds or so. If while he is talking, his signal just disappears and then you can't receive anything... then my friend, your receiver has a problem, and should be returned for service. And you will need to be very clear on the gripe: "When flying formation with another aircraft and he transmits for 30 seconds or so, the receiver stops receiving.... anything and everything.... and then works properly again once it is turned off, cools down, and is turned on again." A tech will immediately know how to test for that with a SigGen.
The above is true, only if I fully understand what you are telling me. If there are further details, the above might be wrong!  I suspect that the first RF amplifier in the receiver, or possibly the first mixer circuit is failing to operate properly. But if I have all this right.... there is no question that your receiver has an issue that needs to be fixed. (Sorry to tell you that).
Mark
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Robin Hou
Joined: 19 Jan 2017
Posts: 15
Location: El Monte, CA
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| Posted: Wed Aug 08, 2018 2:46 pm Post subject: Garmin 250XL Squelch Issue |
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Hi Mark,
You got it right and thank you for your explanation of the SQ button.. There were a few times I stopped hearing the lead while he was transmitting. After a while (after my 250XL was nice and hot), I can no longer hear any transmission from any one.
I can now correctly describe my problem when I send in my 250XL to Garmin for repair.
Your help is greatly appreciated. Thanks again.
Robin
On Wed, Aug 8, 2018 at 12:05 PM Bitterlich, Mark G CIV NAVAIR, WD <mark.bitterlich(at)navy.mil (mark.bitterlich(at)navy.mil)> wrote:
[quote]--> Yak-List message posted by: "Bitterlich, Mark G CIV NAVAIR, WD" <mark.bitterlich(at)navy.mil (mark.bitterlich(at)navy.mil)>
Ok, your description is making some assumptions about what is going on, which I'd advise we not do. I'm still less than clear on EXACTLY what is happening, although we are starting to zero in.
So ... are you saying that when the Icom equipped airplane is close to you, and makes a rather long transmission ... something happens. Question: Do you stop hearing him WHILE he is transmitting, in that he is talking, you hear him, then WHILE HE IS TALKING, YOU STOP HEARING HIM? And then you can't hear ANYONE else? Go through this with me again step by step. Or tell me I've got it correct please.
The most important statement you made was that you could press the SQ switch initially and things would work, and then pressing it again later on..... results in nothing being heard on ANY freq.
Let's talk about that SQ button on your radio so you are clear what it actually does. It does not "reset" ANYTHING. It simply turns Squelch OFF. With squelch off, and the volume turned up, you should be able to hear static in your headset. Try this on the ground with the engine not running, before your flight. Just push the SQ once, listen for static, push it again and the static goes away. So it is a SWITCH ... push once, it turns off squelch, push again it turns it back on.
I think you are getting the wrong idea of what "Automatic Squelch" really is. It is not something that is "adjusting itself" in flight. It is in fact nothing more than a comparator circuit which measures signal to noise ratio, and when the signal to noise ratio achieves a PRESET LEVEL, the speaker is turned on. That is ALL that it does. Pushing the SQ switch just turns the speaker on ALL THE TIME and bypasses this circuit. Pushing the SQ button does nothing to "reset" or "readjust" anything. It just bypasses the circuit that turns your speaker on automatically when there is a strong enough signal.
Now that you understand this, a light bulb should be starting to glow a little bit.
The situation is simply this: You are close to an aircraft with a strong transmitter. I don't believe it has anything to do with the other aircraft having an Icom radio, OTHER THAN, it has been my experience that the Icom Radios put out a tad more power than some others, and also they tend to modulate right at 100%, which is actually a good thing. But the point is that YOUR aircraft is in the near field of this transmission, and that means your receiver is being hit with a ton of energy. And ... I don't believe it is handling it too well at all. Meaning, I think that there is a component in your receiver that is being overloaded and then stops functioning. I base this on one very important point:
You say that once it happens, you can push the SQ button one time, and you hear no static, or transmissions from anyone else. We must be clear on the fact that you now understand that the SQ button is a SWITCH. Hit it once, and it turns the speaker on all the time, hit it again and it goes back to allowing the circuit to turn on the speaker. You need to be very clear on this, and listen to it on the ground with the engine not running, so you can fully understand the function.
If you then go flying again consider pushing the SQ one time, and let it run with the speaker on all the time. It is annoying I know, but do it. Then join and tell the guy in lead with the Icom to transmit for 30 seconds or so. If while he is talking, his signal just disappears and then you can't receive anything... then my friend, your receiver has a problem, and should be returned for service. And you will need to be very clear on the gripe: "When flying formation with another aircraft and he transmits for 30 seconds or so, the receiver stops receiving.... anything and everything.... and then works properly again once it is turned off, cools down, and is turned on again." A tech will immediately know how to test for that with a SigGen.
The above is true, only if I fully understand what you are telling me. If there are further details, the above might be wrong! I suspect that the first RF amplifier in the receiver, or possibly the first mixer circuit is failing to operate properly. But if I have all this right.... there is no question that your receiver has an issue that needs to be fixed. (Sorry to tell you that).
Mark
--
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