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Dean Pichon

Well Known Member
This past weekend, Boston Approach complained my radio transmissions were "barely readable". I have received this complaint periodically though infrequently. This complaint seems most likely when I am at cruise power settings. On the ground or in the pattern, a radio check typically results in a "loud and clear" report.

For equipment, I have an SL-60 GPS/COMM with a PS Engineering PM3000 intercom and Sennheiser noise cancelling headsets.

In all situations, the reception is crystal clear. It is particularly frustrating to have a controller tell me in a clear voice that he cannot understand me. I often wonder if my mike is not picking up cabin noise and transmitting along with my voice.

Any advice on where/how to attack this would be most appreciated.

Thanks,

Dean Pichon
RV-4
 
The first thing I would check is you antenna. Make sure it and all antenna connections are clean and tight. Next check your voltmeter at both low and high power settings. Make sure that you are not getting over voltage at high power settings.
 
I would make sure that you have your mic positioned correctly near your mouth. I realize that is not a very technical solution, but it has made a difference with my DC's at times. There is a bunch of ambient noise in the cockpit at cruise, which can be picked up over your voice if the mic is not right in front of your mouth
 
Thanks guys..

I will check that my antenna connections are clean and tight. The voltage is very stable at all power settings (14.3 volts).

I agree with the mike position comment. I always position the mike so it is just touching my lips.

Thanks,
 
I've had this happen to me twice this year. Both times I could hear fine but the people I was talking to could not hear me well enough to understand me.

First time was on the ground talking to ground control (idle RPM) (switched to tower and they could hear me fine). Second was talking to the wingman just after takeoff (WOT) (switched to unicom and he could hear me fine).

The only similarity with the situations was I had landed and let the airplane sit (not running) on the ground for around 30 minutes.

Valcom 760 radio.
 
i agree with the others ... make sure the BNC connectors on both ends are tight ... after 500 hours we found one of ours came loose, we could hear ... but not transmit.
 
Dean Pichon said:
This complaint seems most likely when I am at cruise power settings. On the ground or in the pattern, a radio check typically results in a "loud and clear" report.

Dean Pichon
RV-4
Click to expand...

On re-reading your post, I think you nailed the problem right here.

Look for something loose. Connectors, or even antenna mounting. Radio ground too.
 
Hi Dean,
Without knowing what season it is in the States right now,I would suspect vent air is blowing on the mike.Even if the air is hitting the back of the mike it will increase transmission noise.

Cheers Nelson
 
Also, reseat the radio and intercomm into their respective trays. The audio and mic are on separate lines. Sometimes reseating the radios, making certain they are fully seated, will make a difference. Check the mic jacks to make certain they are tight and that you are fully seating the mic cord plug into the jack.

Vic
 
Aso check to see if the mike didn't get turned around so you are not talking into the back of the mike. It can happen.
Rich
 
And certainly try a different headset before anything else. The mics can go bad. HOwever, a quick check of the mic can be had by testing the intercomm clarity with another passenger. That should eliminate all wiring to the intercom.

Vic
 
Thanks for the inputs

I should have mentioned in the first post that I have a belly-mounted bent whip antenna. I will definitely check all the connections. Whenever I don the headset I check to confirm the mike is pointed the right way. With Sennheisers, the mike can swivel 180 degrees.

The idea of vent air activating the mike is interesting. This morning I had the thought of doing a "dead air" transmit test and asking the tower what, if anything, was heard. I would believe with a properly working system little if any noise should be transmitted.

Thanks again,
 
Normally if the cause is wind noise, it will trip the squelch of the intercom.
 
I had trouble transmitting until I cleaned the antenna. Just a thought, and it is cheap to do!

************************

As a side note, and not wanting to create thread drift. I am always amazed at the different experiences we all have and the fixes we have encountered that worked. What a great web site!

Now back to your regularly scheduled thread.
 
I suspect the quality of the SL-60 Transmitter

I have an SL-60 and and SL-40 in my RV-6A. Both have their own antenna on the belly. The cases are essentially the same size but the SL-60 has a GPS receiver in it and a lot of extra hardware and software. I was a radio mechanic in the USAF and I have degrees in electronics and computer science so I am not entirely ignorant about the subject of installations, maintenance or operation. I wired in the SL-60 as my #1 com and I used it that way for a couple of years. Often I got the same kind of controller feedback you described. It works but something in the audio, RF or modulation is marginal in my opinion. I switched to the SL-40 as my com radio of choice and I've never had a squawk from the controllers since.

Bob Axsom
 
But if the wind is there during transmit, it will most likely be there during receive as well.
 
Dean,

Your problem is very common in RV's because the noise level in the cabin is usually above 97 decibals in cruise flight which can cause the noise cancelling mikes in your headset to resonate. What the controller or other airplanes hear is a radio that sounds like the modulation is set to high and is likely to be barely understandable. The symtoms will typically go away at lower power settings when the cabin noise comes down which is what you are seeing isn't it? Thankfully Oregon Aero has some nifty little pleather boots that slide over your mikes on EACH headset in the cabin and fix this problem. Every RV'er should have these because we all run at noise levels that make us prone to this whether we are aware of it or not.

Edit... After posting this I noticed that the boots are visable in the picture in my avatar if you are curious what they look like.

Here is a link to Oregon Aeros explanation on the mike problem. http://www.oregonaero.com/p5657_2001.html
A link to the product. http://www.oregonaero.com/p62_2001.html#micmuff
 
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