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SL40 Receiver Problem

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darrell-rv4

Member
I've got a small problem with my Garmin SL40. When flying close (as in close formation), when one of the planes transmits, I just get static. If I pull away maybe 30 or 40 feet, everything comes through just fine. The SL40 has automatic squelch and I've tried to manually adjust it by pulling out the volume knob and rotating it, but no help. Any ideas?
Darrell
 
Could be transponder interference. Have lead turn off the transponder (he should be the only with it on) and see if it does the same thing.
 
The squelch can only be adjusted by going into the menu, pulling the volume knob merely opens the squelch. What you are experiencing doesn't sound like a squelch problem, sounds more like the receiver is being overloaded. I'll look for one of my manuals but I don't thing receiver sensitivity can be adjusted from the maintenance menu.
 
Walt said:
The squelch can only be adjusted by going into the menu, pulling the volume knob merely opens the squelch. What you are experiencing doesn't sound like a squelch problem, sounds more like the receiver is being overloaded. I'll look for one of my manuals but I don't thing receiver sensitivity can be adjusted from the maintenance menu.
Click to expand...

Walt --- I've downloaded the manual for it and searched it for squelch, but couldn't find a spot for adjusting the squelch through the menus. ANY help would be greatly appreciated!!
Thanks.
Darrell
 
I have a SL-30. The squelch adjustment is in the setup mode. To get to setup mode you press the <=> (flip-flop button) and "sys" buttons while turning the unit on. Then turn the large selector knob the the "Com RF Squelch" page. The small knob adjusts the setting. I assume the SL-40 is similar. The directions for doing this are in the installation manual not the operator's manual.

If you are getting static, then I suspect that the squelch is adjusted OK though. I have noticed similar behavior with my SL-30 on certain freqs. when very close to certain other aircraft.

Good luck.
 
It's the same way on the SL-40. Hold down the flip-flop button and the third button in the set of 4 while you power up. It will come up in test mode. Just turn the knob (large one if I remember correctly) to the squelch page setting. Change the number using the little knob, and then push enter or mem (I don't remember which) and it will save it. You will know you got it right as when you start adjusting the number, it will flash. When you hit mem/enter, it will be solid again.

Vic
 
SL40 Receiver

Its a formation thing. It is not likely your radio, transponder (which should be in SBY mode) or your settings of either unit.

I have the same radio and a 430. It's an interfearence created when 2 ships get close. Not every radio is effected. A good flight lead will put you in route before the radio is needed. Good luck with Formation.

Tad "Stripes" Sargent
TeamRV
 
The SL-40's input is more than likely being saturated by the nearby transmission - effectively blocking the signal. Dependent on the design this may be occurring at the input stage (rf preamplifier) or later in the mixer.

Detuning the radio (tune 50kHz off frequency) is one option but this will only work if the saturation is occurring in the post tuning stages (after the mixer).

About the only thing you can do if you absolutely must hear the transmission is to swap the antenna with a 50 ohm dummy load (10 watt minimum from your local ham radio store) for the formation flight. You will be able to communicate within the formation but probably not beyond.

Try contacting Garmin support - see what they say - I'd be interested in their comments.

Doug Gray
 
Doug said:
The SL-40's input is more than likely being saturated by the nearby transmission - effectively blocking the signal. Dependent on the design this may be occurring at the input stage (rf preamplifier) or later in the mixer.

Detuning the radio (tune 50kHz off frequency) is one option but this will only work if the saturation is occurring in the post tuning stages (after the mixer).

About the only thing you can do if you absolutely must hear the transmission is to swap the antenna with a 50 ohm dummy load (10 watt minimum from your local ham radio store) for the formation flight. You will be able to communicate within the formation but probably not beyond.

Try contacting Garmin support - see what they say - I'd be interested in their comments.

Doug Gray
Click to expand...

Doug ---- This is exactly what my hangar partner and I discussed. Do you know if there is an antenna switch which would allow me to go between my normal antenna and the dummy load? Thanks!
 
There are pleanty of 50ohm coax switches and relays out there but the commercial versions are very expensive. Google '50 ohm switch' to get an idea.

You would probably find something more economical and suitable at a Ham radio store. I recall in my Ham radio days seeing rotary switches with multiple 50ohm PL259 connectors on the back - these would work with BNC/PL259 adapters.

Doug
 
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