Intercom or radio transmit issue

Leo O'Farrell

Leo O'Farrell

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Jun 25, 2011
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Lakeport, CA
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Leo O'Farrell
On the past few flights the following issue emerges, usually after 20 or minutes of flight:

The sidetone is lost on all transmissions to the tower or center. They seem able to receive my broadcast transmission, but my voice doesn't seem to broadcast loudly. Calling up ground, tower, or NorCal is usually OK but after a while, I'm fiddling with the squelch to try and hear myself, even testing the intercom without an actual transmission.

Equipment: Old Cessna 172 with 50 Amp alternator; Cheapo push to talk; David Clark ANR headset; PS engineering audio panel; comm 1 is SL40; comm 2 XL250 GPS comm. This issue seems to occur using either radio but only after 20 or more minutes of flight.

I'm thinking I'll swap out the push to talk on the next flight, to see if that makes any difference.

Other troubleshooting ideas?
 
I would be interested in what others say but check your antenna. I just replaced my GPS antenna in a 2007 C182T(G1000) because its connections corroded. Apparently, the factory installed caulking did not do its job.

Doug
 
You should certainly try a different headset, before you dive into the expensive stuff.
 
John221us said:
You should certainly try a different headset, before you dive into the expensive stuff.
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As a professional avionics tech I'll affirm that this statement is the absolute crux of effective troubleshooting.

Learn what you are up against, make a plan and approach it like a crime scene. Because when you start mindlessly fiddling with things, jiggling wire bundles while simultaneously replacing expensive antennas, the symptoms can go away - only to reappear again at an inopportune time.

Avoid what is universally know as the "shotgun" approach, it's gonna leave a big hole in your wallet.
 
I have two thoughts..First we had as similar issue and ended up being the PS engineering audio panel. Cost $400 to send it a way and get refurbished.

we found problem by swapping radios location on the audio panel.

Second thought anything electronic that starts well and goes to pot on a predictable schedule.....could be heat related degradation of the electrical components in the radio.

But I agree start with that is cheap or free to swap out and work up the latter to more and more expensive analysis.

Same way we do it with Computers, Laptops and Networks.
 
Troubleshooting these kind of problems can be challenging and I agree with the recommendation to be analytical about it. If the PS Engineering has a power fail mode (it should), you should be able to turn off the intercom and try communicating without it. I believe my PS Engineering unit is wired so that the pilot jacks are still active on the default radio. Try turning it off and see if it work this way and if it fixes your problem. You should be able to eliminate it. Since you say that it happens on both radios, it and your headset are common single points of failure.
 
Good point, I should be able to shut off the intercom and just use the SL40 once the issue starts and confirm or eliminate the intercom as an issue.

I believe the SL 40 has a built in intercom.

Thanks.
 
This is what's known as T H I N K I N G
 
The SL40 also has an internal intercom and an internal sidetone. These can screw up when coupled with an intercom. For some reason the sidetones on both my SL30 and GNS480 (same comm section) got reset to some level that caused squeals in my intercom.

You can get to the menus to adjust disable these on the SL40 by holding MON down for three seconds..check your pilot guide.
 
Re: Intercom or radio transmit issue- update

Changed out the push-to-talk with a new one yesterday. Flew to Petaluma for a $130 burger (low fuel) and back.

Did not experience the radio transmit issue. This flight required (ATIS, Ground, Tower, NorCal, Center, CTAF just getting there.

So will keep all as is until the next event.

Thanks.
 
The push to talk is really just a binary thing - on or off - so if the radio is transmitting at all then I'd be surprised if replacing the PTT fixed your problem. Have you flown again since? And how are things over at the old T's?
 
pericynthion said:
The push to talk is really just a binary thing - on or off - so if the radio is transmitting at all then I'd be surprised if replacing the PTT fixed your problem. Have you flown again since? And how are things over at the old T's?
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Virtually all aftermarket (i.e. "portable") PTTs have two N.O. contact sets. One set connects the microphone to the mic audio line and the other shorts the Key (transmit on) to ground. The microphone to audio line carries voltage to the microphone's internal amp as well as the audio back to the radio or intercom. If the Key contact works the radio will go into transmit mode and if the mic contacts are corroded the mic audio will be missing or very attenuated. A poor contact on the key line can also cause problems if the radio's key input isn't designed to handle a high resistance (many are not).
 
Ah! Makes sense. But why are they designed like that - why disconnect the mic audio line at all?
 
pericynthion said:
Ah! Makes sense. But why are they designed like that - why disconnect the mic audio line at all?
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Two reasons. One is so two or more microphones can be plugged into the same radio and the other is that many handheld radios sense the load on the mic bias instead of the key to activate the transmitter. BTW the dual contact PTTs can prevent an intercom from working.
 
Yup. I've flown one aircraft with a badly configured intercom that had separate keying without a path to define which mic was live at PTT. ATC could hear everyone on board with a mic when the PTT was pressed on either left or right yoke month ideal when kids or talkative adults who won't maintain a sterile cockpit are on board.
 
OK, believe that I have identified the culprit, my David Clark noise canceling headset.

Went bad quickly on a flight today. Was able to swap in my original DC headset and all good, just louder.

Going to send the ANR headset back for repair.

Leo
 
Leo O'Farrell said:
OK, believe that I have identified the culprit, my David Clark noise canceling headset.

Went bad quickly on a flight today. Was able to swap in my original DC headset and all good, just louder.

Going to send the ANR headset back for repair.

Leo
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I couldn't say this while I was in the business of designing and selling headsets, but now that I'm out of that cutthroat business, I'm free to express my opinion.

My opinion is that the ANR headset is the best boondoggle to be foisted on the flying community since the hydrogen gasbag on airships. A good passive noise deadening headset is quite adequate to filter noise down well below an acceptable level and is damn near foolproof. ANR requires precise balancing of microphone-earpiece circuits and has more parts to fail than the average intercom.

And besides, I *WANT* to hear my motor. I *WANT* to be tuned into what sounds right and what may be an incipient character-building experience.

I spent several thousand hours without a headset at all, and I'm sure my hearing suffered. Only when I started learning how to design passive noise-deadening headsets properly did I regain some of the hearing that I lost, but some of it is gone forever.

Suggest that you *JUNK* your ANR or pawn it off on somebody that doesn't read this NG and go back to your good Davie Clucks or whatever other good passive headset you prefer.

Just my 8% of two bits.

Jim
 
weirdjim said:
I couldn't say this while I was in the business of designing and selling headsets, but now that I'm out of that cutthroat business, I'm free to express my opinion.

My opinion is that the ANR headset is the best boondoggle to be foisted on the flying community since the hydrogen gasbag on airships. A good passive noise deadening headset is quite adequate to filter noise down well below an acceptable level and is damn near foolproof. ANR requires precise balancing of microphone-earpiece circuits and has more parts to fail than the average intercom.

And besides, I *WANT* to hear my motor. I *WANT* to be tuned into what sounds right and what may be an incipient character-building experience.

I spent several thousand hours without a headset at all, and I'm sure my hearing suffered. Only when I started learning how to design passive noise-deadening headsets properly did I regain some of the hearing that I lost, but some of it is gone forever.

Suggest that you *JUNK* your ANR or pawn it off on somebody that doesn't read this NG and go back to your good Davie Clucks or whatever other good passive headset you prefer.

Just my 8% of two bits.

Jim
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Jim there are several significant benefits to ANR vs passive headsets (and hearing protection probably isn't one of them). First and foremost they are generally way more comfortable and I place a fairly high value on my comfort. The clamping pressure required to provide adequate Second they definitely reduce fatigue on long flights and IMO this is a noticeable safety enhancement as fatigue is high on the list of secondary accident causes. Third they make for greatly improved listening to the voices on the other side of the radio. I've found that as my ears get older it's a lot harder for me to understand ATC with a good passive headset than with my Zulus.

There are folks you claim that ANR does provide better hearing protection but I'm not convinced of that for the most part (see below). The best ANR is only effective at reducing sound in the 100-500 Hz range and it's my understanding that most aviation induced hearing damage occurs at higher frequencies. That said it might be that ANR does help with this by eliminating the need to turn the radio volume up as high.

In some airplanes (not so much in my Baron), some of the better in-ear passives work about as well as a good ANR without the complexity and potential for failure (not to mention battery consumption) that comes with ANR.

As to the issue of "hearing your motor" I'd have to admit there are plusses and minuses with ANR. Because the ambient noise is lowered and you can have the radio volume down as well with ANR it's definitely possible to hear things happening to your engine that you'd miss without it but I don't doubt the same can be said the other way around. Keep in mind that ANR affects only a small portion of the audio spectrum and those "funny engine sounds" can occur all over said spectrum. One thing I can say for certain is that I can hear the stall and gear warnings a lot better with ANR on vs off and that's worth something too.
 
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I love my QT Halo - just as quiet as ANR but far more comfortable than any conventional headset (ANR or passive). I'll never use a head-clamper again.
 
weirdjim said:
And your qualifications for being in the design and test of aircraft headsets are ???

Jim
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Jim,

I've never designed an "aircraft headset" but I probably could if I wanted to. I have designed echo cancelling audio processors for telephone systems several years ago using similar concepts to ANR headsets but there are a lot of differences as well. As to "testing" I have used several different ANR headsets for over 25 years including some unofficial "beta" testing for Alan Schrader (Lightspeed) and have had many extensive discussions with him regarding various ANR design concepts.

But I fail to see where you're going with this, anyone who's used ANR headgear will likely have their own opinion WRT their effectiveness and I think I'm entitled to express mine as you did yours.
 
Here's what David Clark has to say about the headset:

We are in receipt of your headset for repair and have determined the following charges due the unit being outside our five year warranty. Your headset has a date of manufacture of May 2004.

Replace: Mic, PC Board & Seals $70.00
Shipping and Handling via Trackable Ground Service +13.00
TOTAL $83.00

Seems reasonable. Think it must of been on the shelf for a couple of years at the airport shoppe in Ried Hillview before I paid over 700 bucks for it new.
 
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