RE: SL40 Comm Problem

fstringham7a · #1 02-03-2010, 03:46 PM

HI

Since N74BZ ( aka BUZZ) flew the first time there has been a problem with my SL40 Com. When I push to talk it gives a loud squelch like noise that continues until the push to talk is released. Reception is clear has a bell.
No problem with the PTT using the 430 com......Any ideas.

Frank @ 1L8 ...RV7A... Flying

Peterk · #2 02-03-2010, 03:59 PM

Be sure your headphone setting on the SL40 is at zero.

noelf · #3 02-03-2010, 04:09 PM

...now is a good time to check the Garmin web site for SB: 0921 RevA that has been issued for the SL40 and SL30 and compare with the Mod's listed on your unit.

Ted Radclyffe · #4 02-03-2010, 08:20 PM

I experienced, with my SL30, a very similar problem.
The intercom was fine, reception was OK, but when transmtting I got a buzzing noise in the headphones and complaints that I was scratchy. This developed over time.
I reasoned that the problem related to a rapidly changing transmitter power which in turn changed the sidetone volume. (I.e a changing VSWR rapidly changing the current drawn by the set on transmit)
I checked all the connectors and coax and the point at which the antenna was bolted through the hull incase there was corrosion or something loose. All was OK.
A flick of the antenna whilst transmitting on the ground confirmed that the problem related to the antenna which turned out to be a hairline crack almost all the way through the stainless steel bent rod. On the ground everything was more or less OK but in the air, it vibrated probably in rough time with the engine or air turbulence.
$200(Aus) later, the new antenna fixed the problem.

I don't know if this helps in an way, but my strong suggestion is to look to external problems rather than internal problems with the set. Start at the connector at the back of the SL40 (which is actually loosly mounted in the cradle) chase the coax run for chafing, flick the antenna whilst transmitting and see if any of these things induce or ameliorate the problem.

Ted
(RV-6A "Rough Red")

lrfrey · #5 02-04-2010, 08:57 AM

Frank, I had a similar problem with my SL30, I would describe my symptom as a squeal tho. In my case only the co-pilot side did it, can you isloate it to one set only? My problem turned out to be the antenna coax and co-pilot mike coax running side by side for about 10 feet. Re-routing eliminated the problem.

Echoing Ted I would suspect the problem to be external to the SL40. If the problem only exists on the pilot side, suspect something ahead of the SL30 (headset wiring etc). If it exists for both sides, suspect something behind the SL40 (wiring/ground beyond intercom, chasis seating, antenna etc)

Larry

vlittle · #6 02-04-2010, 09:55 AM

I've had a squeal with my SL-40 using a Halo headset. This problem only occured on the ground.

The simple fix was about 3 turns of the headset cord, 2" in diameter, held together with tie-wraps. This simple RF choke solved all of my problems.

Easy to try.

Vern

Bavafa · #7 02-04-2010, 06:26 PM

I have had similar issues with my side tone on the SL-40 compared to the 430. I have played with the side tone on the SL-40 and it is quite bare able but it is not as nice and clean as the 430, it just sounds different. Reception is as clear as it can be. Humm, I guess some more troubleshooting is in order, as I thought that is inherent to SL-40.

Steve · #8 02-05-2010, 09:14 AM

How close are the antenna and the mike to each other? I know its had to get any appreciable distance between the two in an RV. But I had a similar issue depending which headsets I used. My cheapo $100 Pilots made feedback squeals while my better Telex were quiet. I have my Rami antenna mounted forward of the spar, inboard of the left gear leg on my 9A.

arffguy · #9 02-05-2010, 01:52 PM

I agree with the ideas above. What intercom are you using? Some intercoms don't play well with other radios without some mods internally. I am dealing with a similar issue right now on a Cessna. Have you run this past the manufacturers? I am suspecting bad grounds on my issue.

Mine squealed with the engine running. At first I suspected the alternator diodes had a problem. Turned off the alternator but left the master on and radio sounded fine. Tested the alternator and came out good. Chasing the wiring now.

But then again, you did nickname the plane "Buzz"

fstringham7a · #10 02-05-2010, 03:04 PM

I have used two head set to check the problem....Pilot (passive nr) and QT Halo (which I am still trying to get to work.....another thread I see coming), archer wing tip antenna (com2...com1 is a belly whip just aft of the spar web), and a Garmin GMA 340 Audio Panel.

I did go in and change both mic outputs to zero. This helped. The Pilot head set now can transmit clear as a bell....but rhe QT is intermittent . But like I said I am working with Phil to get the QT to work as advertized. (Basically when I talk intercom or transmit it will cut out. About a month ago Phil suggested I open the box and cut out a diode??????as I rememebr. he said the gain is to high and this would reduce it.......as I remember the conversation.

So I THINK I have fixed the problem by reducing the mic 1 and 2 to zero on the SL40. I will be flying next week....weather permitting....and will check it in the real environment.

Frank @ 1L8 ...RV7A... flying