[Veetail88]

Folks, I'm having a problem with my SL40.

As this is my only on board radio I need to solve this rather quickly and don't really know where to start, looking for suggestions.

I have an SL40 transceiver wired to a GMA 240 audio panel. This is a new installation as we just started flying.

The problem is that the unit is transmitting fine it seems, but the reception is very weak and crackly to nothing at all.

On the ramp, and standing 20' away with a handheld, everything seems fine. In fact, often, inside the hanger I can receive other aircraft outside.

Once the engine is fired up and taxiing to the runway and all during flight, the reception gets horrible or worse.

Right now, I know the wiring from the audio panel is fine as audio from the EFIS to the head set is fine. I'm not sure at the moment if anything gets from the radio to the headsets or not. Waiting on an answer from Jeff Point (my test pilot) as to whether or not he was able to un-squelch the radio in flight and at least get static in his ears.

Do I look to the antenna? I'm not a radio guy, but it seems that must work fine if the transmit function works ok, but I've been wrong now and again.

The radio tray came with a 90 degree antenna attachment on the back of it. Are these things ever a problem?

Do new radios ever ship defective?

Just looking for some direction here. No experience what so ever in this kind of stuff. Thanks for your help.

 

[Jesse]

I'd recommend checking for a short in your antenna cable and maybe try checking the antenna. Also, try plugging your radio into a plane with a known working installation and narrow it down to the radio itself or the installation.

 

[sprucemoose]

I'll chime in here with more data. In flight the reception was almost nonexistent. I did pull the squelch knob out, normally that results in static but all it did in this case was allow very faint receptions to be heard. Oddly, the problem got better closer to the ground; at 3500 AGL reception was horrible, at patterns altitude it was a little better, and on final (few hundred AGL) it was better still. Once back on the ground I could hear OK again. Other aircraft and ground stations all reported hearing my transmissions just fine, which would argue against it being an antenna problem, even though the other symptoms suggest so.

 

[BobTurner]

Once the engine is fired up and taxiing to the runway and all during flight, the reception gets horrible or worse.

lp.

My guess is that something associated with the engine is emitting RF and interfering with the receiver. Try alternator off, one mag off, etc., see if you can narrow it down or confirm this.

My wild guess is a defective spark plug lead.

 

[noelf]

I work at an FAA authorized avonics repair station in Sanford,NC. If you were to bring in the SL-40 for a bench test, we most likely would do it for free. It is a rather quick test if you walk in with the radio: receiver sensitivity and audio quality, transmit power out, VSWR, frequency stability, squelch test, etc.

If we determin there is a problem with the radio, we send it (or you can) to Garmin. If the radio checks fine then we would talk to you about looking into the rest of the aircraft...at whatever shop rate gets negotiated with you.

I am not saying all shops do this, but it might be worth looking into finding a shop close by that will give a thumbs up/down on the radio by itself.

 

[Veetail88]

May have solved the problem.

Having pulled the radio so I could test the coax for a short and sliding it back in, I found I had no audio at all. Pulled the radio back out, re-inserted it and I could hear again. On further investigation and thought regarding the installation in the first place, I suspected the radio wasn't seating into the tray completely, and therefore nor were the connectors. I'd taxied the airplane out and tried talking with another guy on the ground with a handheld, and the issue sounded like a poor connection as well.

I hacked away at my panel a bit so it wouldn't interfere with the insertion and the unit was able to go in about 1/8" further into the tray.

A subsequent trip out onto the taxiway with the engine running produced a loud and clear radio check with another guy 3 miles out.

Hopefully the next flight test will confirm problem solved.

Thanks for you help folks!