Broken & Unreadable on Certain Frequencies

itsjames2011

itsjames2011

Pre-takeoff checklist
Joined
Jul 21, 2014
Messages
165
Location
Chicopee MA
Display Name
Display name:
James
Hey everyone,


I am pulling my hair out with my continued radio woes and would appreciate any advice. Westover tower and ground hear me great from 50 miles away on 134.85 and 118.35. Northampton unicomm and turners Unicomm hear me great on 122.7 and 123.0 yet Westfield Tower 118.9, Worcester Tower 120.5 and Bradley Departure 125.35 all say I am broken and unreadable even when I'm in the pattern and can see the tower!

I have 2 seperate antennas in the airplane. I have tested them both with an analyzer and the vswr is 2:1 or less across the whole band.

I also tested them with a seperate swr and power meter using the radios themselves and I am seeing a good 5-6 watts of output regardless whether I am on one of the good frequencies or the bad frequencies.

I have tried 2 seperate KX-175B's, an MX170, and have confirmed via an external frequency counter that they are transmitting on the correct frequency and have not drifted.

3 Seperate radios, 2 seperate antennas, same behavior regardless of the setup. Anyone care to speculate as to why I would be broken and undreadable on only certian frequencies when all of the equipment checks out okay?



My equipment list is as follows.
4 x Bose A20 Headsets
David Clark 4 Place Intercom
2 x KX175B Radio
Collins AMR-350 Audio Panel
 
I feel your pain. I have had the same problem on certain frequencies except in in my case it is broken unreadable in receive on certain frequencies.
 
itsjames2011 said:
Hey everyone,


I am pulling my hair out with my continued radio woes and would appreciate any advice. Westover tower and ground hear me great from 50 miles away on 134.85 and 118.35. Northampton unicomm and turners Unicomm hear me great on 122.7 and 123.0 yet Westfield Tower 118.9, Worcester Tower 120.5 and Bradley Departure 125.35 all say I am broken and unreadable even when I'm in the pattern and can see the tower!

I have 2 seperate antennas in the airplane. I have tested them both with an analyzer and the vswr is 2:1 or less across the whole band.

I also tested them with a seperate swr and power meter using the radios themselves and I am seeing a good 5-6 watts of output regardless whether I am on one of the good frequencies or the bad frequencies.

I have tried 2 seperate KX-175B's, an MX170, and have confirmed via an external frequency counter that they are transmitting on the correct frequency and have not drifted.

3 Seperate radios, 2 seperate antennas, same behavior regardless of the setup. Anyone care to speculate as to why I would be broken and undreadable on only certian frequencies when all of the equipment checks out okay?



My equipment list is as follows.
4 x Bose A20 Headsets
David Clark 4 Place Intercom
2 x KX175B Radio
Collins AMR-350 Audio Panel
Click to expand...

Just as a first shot out of the box, and while I wake up, disconnect the ELT from its antenna by separating the antenna cable from the ELT by just disconnecting the cable connector from the ELT connector and letting the cable dangle loose (or tie it up if it will drift into the mechanisms).

Even better, find somebody with a handheld at the other end of your airport and see if THEY report you as broken/garbled in a quick test on your bad channels (so as to not mess up the legit stations on these frequencies). THEN disconnect the ELT antenna and see if the problem cures itself up.

Jim
 
I will go try this in an hour or so. If it matters, I have one of the new 406mhz ELTs

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Pulling the antenna off of the ELT did not change a thing

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For what it's worth if I use the hand mic I go from broken and unreadable two weak but legible

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itsjames2011 said:
For what it's worth if I use the hand mic I go from broken and unreadable two weak but legible
Click to expand...

which audio panel do you have and how are you plugging in the hand mic?

I've heard stories (but have no experience with because of the way mine was installed) that some of the PS Engineering panels have problems if the original hand mic socket is left in the system. The shop that did the installation pulled the hand mic socket and another shop confirmed that it was the proper thing to do although the technical description was limited to "the audio panel has problems if you leave it in"
 
Clark1961 said:
which audio panel do you have and how are you plugging in the hand mic?

I've heard stories (but have no experience with because of the way mine was installed) that some of the PS Engineering panels have problems if the original hand mic socket is left in the system. The shop that did the installation pulled the hand mic socket and another shop confirmed that it was the proper thing to do although the technical description was limited to "the audio panel has problems if you leave it in"
Click to expand...
The audio panel is an old Collins AMR 350 and I do not normally have the hand mic plugged in at all, I just plugged it in on a whim for a test.

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itsjames2011 said:
The audio panel is an old Collins AMR 350 and I do not normally have the hand mic plugged in at all, I just plugged it in on a whim for a test.

Sent from my SAMSUNG-SM-G920A using Tapatalk
Click to expand...

Just for reference, what's the airframe.

If I knew your ELT was one of the 400MHz new units I wouldn't have suggested pulling the antenna. The old ones could develop a strange varactor maser action with the C-B junction of the output transistor.

Now we can start doing some work that the hand mic seems to somewhat cure the problem. WHen reported "weak" who was the reporting station and SHOULD you have been weak at your distance?

Jim
 
It's a 1964 Cherokee 140 and the tower that said I was weak was a mile away I could see it at 3000 feet

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itsjames2011 said:
It's a 1964 Cherokee 140 and the tower that said I was weak was a mile away I could see it at 3000 feet

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Click to expand...

OK, now that we know that the hand mic "cures" the problem, let's think about whether the tower said you were "weak" because the AUDIO % modulation was down in the mud or whether the actual carrier strength was weak.

Try a couple of the known "good" stations with the hand mic and ask if the modulation seems to be low.

Jim
 
Yep the modulation was low at my home field on 134.85 yet it was fine on the headset.

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Since it doesn't appear that anyone here has any theories, does anyone know if there's a place online that specializes in this kind of thing? The local avionics shop doesn't seem to have a clue what they're doing and I'm not really looking forward to the drop the airplane along with a blank check game.

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itsjames2011 said:
Since it doesn't appear that anyone here has any theories, does anyone know if there's a place online that specializes in this kind of thing? The local avionics shop doesn't seem to have a clue what they're doing and I'm not really looking forward to the drop the airplane along with a blank check game.

Sent from my SAMSUNG-SM-G920A using Tapatalk
Click to expand...

Sure, we've all got theories, and that's why I asked you the question about the hand mic. Seems to me that the headset is bollixing up the works in some way, whether that be RF getting into the headset or some other obscure problem with the audio system.

But if you don't want to pursue this line of troubleshooting, that's fine by me too. It is just difficult to do online what would take me less than half an hour do do in person.

Try another make or model of headset and report back.

Jim
 
weirdjim said:
Sure, we've all got theories, and that's why I asked you the question about the hand mic. Seems to me that the headset is bollixing up the works in some way, whether that be RF getting into the headset or some other obscure problem with the audio system.

But if you don't want to pursue this line of troubleshooting, that's fine by me too. It is just difficult to do online what would take me less than half an hour do do in person.

Try another make or model of headset and report back.

Jim
Click to expand...
If I could bring it to you and pay you to fix it I totally would as the guy at the local shop seems completely clueless.

I have tried 2 Bose A20 headsets, a David Clark H20-10 and one of the ASA ones as well. Everything worked fine for the first 5 months I had the plane and then out of the blue this just started. I'm willing to try anything that's going to get this fixed.



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Ah, quick question. Is the jack that you are plugging the hand mic into the same jack that you are plugging the headset mic into?

Jim
 
weirdjim said:
Ah, quick question. Is the jack that you are plugging the hand mic into the same jack that you are plugging the headset mic into?

Jim
Click to expand...
Hand mic into both jacks, same result.

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This may be a long shot, but I've had various radio problems recently in my Archer caused by USB charging adapters plugged in to the lighter socket. One of them caused both my GTN 650 GTS/nav/com and older King com to go haywire when plugged in.

I have heard rumors that Griffin at Hyannis is good at troubleshooting older avionics
 
itsjames2011 said:
Hand mic into both jacks, same result.

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Click to expand...

So we know that the hand mic works, although the % modulation is down, in both jacks and that the headset with good modulation works on some frequencies and broken/unreadable on others.

Do you have access to a handheld radio and a friend willing to spend an hour or so troubleshooting?

Jim
 
weirdjim said:
So we know that the hand mic works, although the % modulation is down, in both jacks and that the headset with good modulation works on some frequencies and broken/unreadable on others.

Do you have access to a handheld radio and a friend willing to spend an hour or so troubleshooting?

Jim
Click to expand...
I do, tell me what we need to do :)

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OK, we are going to do something that some netnanny will brand as illegal. (S)he MAY be correct, but it is the only way I know (absent a really good/expensive service monitor) to find out what is going on.

Make a list of your good/bad frequencies. Have your friend with handheld go to the other end of your airport from your airplane. Start out with frequency #1. Let's say it is 122.9. Key your microphone and say the frequency ("122.9"). Have your friend read back the frequency or say "unreadable". Go to the next frequency. And the next. And the next. If the same frequencies that were formerly bad are still bad, that's good. At least we have a base problem that is stable.

Then let's choose some semi-random frequencies. How about 118.0, then 119.1, 120.2, and so on. Repeat above test. Report back.

Jim
 
Okay Jim so we tried it on the ground with 2000 feet of separation with the airplane running and the airplane off and all of the frequencies sound fine. I then took off and tried to talk to Westfield tower and Bradley approach and Both said broken and unreadable yet Westover could hear me fine

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Was the airplane set up exactly the same way for both the ground test and flight test? Any differences such as strobes off and then on or transponder set to STBY and then ALT? How do your static wicks look?
 
SkyDog58 said:
Was the airplane set up exactly the same way for both the ground test and flight test? Any differences such as strobes off and then on or transponder set to STBY and then ALT? How do your static wicks look?
Click to expand...

I configured the airplane the same as enroute. Master, radio master, strobes, transponder set to ALT.
 
itsjames2011 said:
Okay Jim so we tried it on the ground with 2000 feet of separation with the airplane running and the airplane off and all of the frequencies sound fine. I then took off and tried to talk to Westfield tower and Bradley approach and Both said broken and unreadable yet Westover could hear me fine

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Click to expand...

Aw, please. If you want my help, follow my rules. Nobody asked you to start the engine and fly. And you didn't bother to do the second part of what I asked you to do.

One of two things is going to happen. You are going to follow my troubleshooting procedures, or,

Two, you are going to find a shop that will take your money and perhaps find the problem.

Your choice. Let me know what you want to do.

Jim
 
weirdjim said:
Aw, please. If you want my help, follow my rules. Nobody asked you to start the engine and fly. And you didn't bother to do the second part of what I asked you to do.

One of two things is going to happen. You are going to follow my troubleshooting procedures, or,

Two, you are going to find a shop that will take your money and perhaps find the problem.

Your choice. Let me know what you want to do.

Jim
Click to expand...
I did do the second part of what you asked me to. The bottom line is that every frequency sounds okay between the airplane and the handheld. I did frequencies that I know are good, I did frequencies that I know are bad, & I did about 10 or 11 random frequencies. Every single one was loud and clear.

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itsjames2011 said:
I did do the second part of what you asked me to. The bottom line is that every frequency sounds okay between the airplane and the handheld. I did frequencies that I know are good, I did frequencies that I know are bad, & I did about 10 or 11 random frequencies. Every single one was loud and clear.

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Click to expand...

OK, now fire up the airplane and repeat these ground tests to the handheld with the engine around mag check RPM (1700 or whatever you normally use).

Thanks,

Jim
 
weirdjim said:
Aw, please. If you want my help, follow my rules. Nobody asked you to start the engine and fly. And you didn't bother to do the second part of what I asked you to do.

One of two things is going to happen. You are going to follow my troubleshooting procedures, or,

Two, you are going to find a shop that will take your money and perhaps find the problem.

Your choice. Let me know what you want to do.

Jim
Click to expand...

:rofl::rofl:

Is it difficult climbing up on that high horse?
 
I gotta side with Jim. Many times I've been asked how to do something then the asker does it his way anyway. You gonna troubleshoot do it logically. That's the point Jim's trying to get across.
 
Norman said:
I gotta side with Jim. Many times I've been asked how to do something then the asker does it his way anyway. You gonna troubleshoot do it logically. That's the point Jim's trying to get across.
Click to expand...

It seems to me that the guy did what Jim asked but then did a little more and Jim is irate for him doing so. How dare he go fly his own airplane while he was out at the airport and had it out of the barn and in condition to fly. Really?

Don't get me wrong, from the posts of his that I have read Jim gives great advice and seems to be very knowledgeable. However he also seems to be a little full of himself.
 
SkyDog58 said:
It seems to me that the guy did what Jim asked but then did a little more and Jim is irate for him doing so. How dare he go fly his own airplane while he was out at the airport and had it out of the barn and in condition to fly. Really?

Don't get me wrong, from the posts of his that I have read Jim gives great advice and seems to be very knowledgeable. However he also seems to be a little full of himself.
Click to expand...

No, I just hate wasting time when we already know the answer. We've got 760 degrees of freedom in choosing a channel and I was trying to eliminate as many of them as possible with as few tests as possible.

What has me going is the fact that he swapped known good radios, known good headsets, and it works just fine with the hand microphone, albeit down in modulation. His VSWR tests on the antenna virtually eliminate that from contention. And, it happens on only two frequencies that we are aware of and I'm trying to find some correlation between all this mess.

I'm sort of stuck on it being a case of way, way overmodulated carrier but can't prove it. And why only those two channels? So far nothing makes sense and I wish to the holy St. Potluck I could stick my spectrum analyzer on the sucker and find out why it was distorting so badly. I'm leaning to the side of RF getting into the microphone wiring but why does the hand mic work just find and the headset mic distorts? Makes no sense. No sense at all.

Oh, question. When you did the engine off ground test with the handheld radio, did you do it in the configuration you used when you fly? That is, if you had the transponder on and/or the panel lights and/or the fribbish on, did you have this same configuration fired up when you did the handheld test?

Not braggin' on myself, just a note that I started working in the local TV shop when I was 12 (you could do it back in the '50s before the do-gooders passed the "child labor" laws) and I'm 72. That's 60 years of tracking the snaps, crackles, and pops of errant electrons and I've developed a divide-and-conquer mentality about how I troubleshoot. I've seen WAY too many "technicians" start throwing parts at a problem until one of them sticks ... a technique called "shotgunning" the problem and sometimes it works, more often not. That ain't my style and it ain't my persuasion. As the saying goes, if you don't want my peaches, don't shake my tree.

Now, let's get back to fixing this dang radio/airplane.

Jim
 
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I just reread the whole thread. I wonder if you've got somebody on the field with an old Telex or other headset with just a normal aircraft dynamic or carbon microphone you can use. Practically no electronics in either of those to bollix up the test. But yet you can use your Bose without the engine running and things seem to be OK. Confusing, confusing.

Try the test again with the "bad" frequencies and the engine running and switch off ALL the other electrics in the airplane ... pull the breakers if you have to and shut EVERYTHING down except the radio under test. Especially everything with an electric motor in it like the turn&bank. Can you turn off the alternator field on your airplane with the engine running?

Jim
 
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weirdjim said:
OK, now fire up the airplane and repeat these ground tests to the handheld with the engine around mag check RPM (1700 or whatever you normally use).

Thanks,

Jim
Click to expand...
We repeated the test with the airplane running and the RPM's at 2000. Now the frequencies that I know are bad are broken and unreadable, the frequencies that I know are good are clear and random frequencies are also clear.

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weirdjim said:
I just reread the whole thread. I wonder if you've got somebody on the field with an old Telex or other headset with just a normal aircraft dynamic or carbon microphone you can use. Practically no electronics in either of those to bollix up the test. But yet you can use your Bose without the engine running and things seem to be OK. Confusing, confusing.

Try the test again with the "bad" frequencies and the engine running and switch off ALL the other electrics in the airplane ... pull the breakers if you have to and shut EVERYTHING down except the radio under test. Especially everything with an electric motor in it like the turn&bank. Can you turn off the alternator field on your airplane with the engine running?

Jim
Click to expand...
I was able to turn off all of the strobes, the lights, the fuel pump, and the transponder. I do not have a two-part master switch you cannot turn off the alternator. With everything that I can turned off the problem is still there.

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OK, I've got my hands full this afternoon. I'm going to go through this thread post by post and summarize what we have done this evening. Maybe if we look at it long enough we can see something that we can't see post by post.

Jim
 
Stupid question perhaps, but does the frequency that ATC has a hard time hearing you have a liveATC feed? Might we learn anything about the nature of the problem by hearing his transmission from the air in a LiveATC archive?

Yes, I know it's just some guy on the internet recording transmissions from his scanner with a crappy antenna in some undetermined location, but perhaps it would tell you something???
 
Brad Z said:
Stupid question perhaps, but does the frequency that ATC has a hard time hearing you have a liveATC feed? Might we learn anything about the nature of the problem by hearing his transmission from the air in a LiveATC archive?

Yes, I know it's just some guy on the internet recording transmissions from his scanner with a crappy antenna in some undetermined location, but perhaps it would tell you something???
Click to expand...
It does. I will cut down the mp3s and post them in an hour or so.

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Unscrew the power connector from the turn and bank if you have no other way to kill it.
 
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