R

Rockyjs

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This is a brand new SL-30 that sends out carrier only no modulation. I've checked all the wiring, antennas and even swapped positions on my audio panel with my GNC 300XL. The unit receives, but the quality is unknown. The recommendation of the dealer is to wait till I'm on ships power, but the unit is rated 10-40 volts, and with my battery charged I'm showing 12.2 volts. When I key the radio it cuts off the modulation in my hangar FM radio.

I pulled the radio out of the plane and checked the antenna couplings on the back of the radio. Both the NAV and COMM show continuity from the center pin to the outside of the connector. This doesn't seem correct to me. I'm getting ready to send the unit back, but just want to make sure I've covered all the bases.
 
If it's sending out a carrier, it's probably not the antenna connections. If you're checking continuity from center to shield in the tray, disconnect the antenna side of the coax before you pull out the ohm meter. Some antennas have baluns or other matching networks that will look like a DC short (almost always the case for a nav antenna). If you're checking it at the radio...don't. Who knows how they built the radio, checking continuity on an antenna port without a service manual isn't going to tell you anything.

I'm not sure how cutting out the modulation on your FM radio has anything to do with it; it's probably just overloading it with RF. Since they are on different frequencies, and using different modulations, all it's really telling you is your FM radio is susceptible to interference.

I'd investigate the usual causes, mic wiring, radio configuration (there are two mic inputs on the SL-30, you can select which mic to use for transmit in the menus), mechanical connections (pins not seated, etc), and finally make sure the radio is firmly seated in the tray.

If the voltage is above 12V while you're transmitting, I don't see that causing it. My SL-30 certainly doesn't have a problem transmitting at 12V.

The SL-30 has the capability to receive NOAA weather radio in the 162 MHz range; you might be able to use this feature to check out the receiver.

Good Luck,
Paige
 
Do you hear a sidetone in your headset when you try to transmit? If so, your MIC and associated wiring is probably correct. There are also configuration options that adjust both the MIC gain and sidetone levels, these are accessible via the front panel.
 
There is a selection in the software via front pannel for mic 1 & mic 2, on or off.
Good luck,
Rich
 
Thanks for the replies. I've rechecked everything several times. We placed this radio in another RV-7 under construction and got carrier only no modulation. When I adjusted the microphone gain up to 220 (default 120) it finally transmitted with modulation, but was garbled and unacceptable. My next step is to swap a known good radio into my panel, but I wanted to make sure that I am not overlooking something
 
Sounds to me like you're doing all the right troubleshooting steps - suspect radio in good ship, good radio in suspect ship....if the problem truly is in the SL-30, then I would strongly suspect a software setup issue (at least that has been my experience) - usually it takes another set of eyes to spot something obvious.....(at least in my experience...).

Paul
 
Finally it works

Good News! I now have a transmitting SL-30. After about 12 hours of troubleshooting, I borrowed a fellow builders brand new radio and installed it in my panel. It didn't work either so I removed it. I tightened both the comm and Nav antenna couplers.I did find that on the right side there was some slight binding with the instrument panel. I filed both sides and re-installed my radio. That did it! There is a note in the install manual about ensuring that the radio fully seats, but I was lulled into believing that wasn't my problem, since this very radio did not function in another aircraft with a bare radio stack. Thanks again for all the suggestions.
 
I just installed my SL 30 and have the opposite problem that Rocky had. It receives great, but as soon as the Mic key is depressed it sends out a tremendous squeal heard both in the headset and over the air. Has anyone seen this before? The Mic works fine as an intercom. I don't have a Nav antenna installed but don't see how that would matter.Thanks

Larry
 
I haven't seen it on the SL-30, but I have seen it in other radios.

The following advice assumes you don't have an audio panel. It also assumes there isn't an external audio feedback source. If your mic is too close to a cabin speaker, or a scanner, you'll get audio feedback.

Some causes are:

1) Bad comm antenna... double check your antenna connections (and make sure you're connected to the comm antenna and not the nav antenna), disconnect the coax and check the coax for shorts.

2) Low voltage... measure the voltage when transmitting

3) Audio feedback

3.1) Disconnect the mic and transmit; if that fixes it, try a different headset or adjust the mic gain setting in the radio

3.2) If the problem continues with a disconnected headset, remove the radio from the tray, and check the audio connections (as in aircraft wiring, not the radio itself) with an ohmmeter, look for any readings between audio input lines and audio output lines.


There are probably other reasons, but those are the ones I've seen.

YMMV,
Paige
 
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Thanks Paige. Did all the things you suggested and a few more. During the trouble shooting process I found a few new clues. First it only did it on the co-pilot side. Second, it did not do it with a different headset. Hummmm.

After trying everything I could think of and talking to both the Com and Intercom techs I ruled out the Intercom, as I was told it is completely out of the circuit during transmit, it merely passes the signal thru via a relay. I ruled out the Com as no matter which mic (pilot or co-pilot) is transmiting, the radio sees it on the same single wire.

Hummm. RF? I stood there for about 20 minutes asking myself "What's different between the two circuits?" Both wired the same, both eqidistant from the antenna, both wired with shielded cable etc.

The only difference was the co-pilot mic cable and the antenna co-ax ran down the same conduit. Re-routed the antenna co-ax and problem gone!

RF is funny stuff. I still don't quite get it as the mic cable and antenna co-ax still run through the same conduit for about three feet, I just moved the last three feet. Maybe this will help someone else, the whole process took about 9 hours!

Larry
 
Glad you got it fixed.

Some mics are more sensitive with respect to RF than others. And the fact that our radios are AM doesn't help matters.

One other thing I forgot to mention in the discussion was checking the ground at the antenna. A bad antenna ground will cause the coax to radiate, and couple RF into surrounding circuits.

Cheap coax can also cause RF to be coupled into surrounding wires, although probably to a much lesser degree than a bad ground, bad antenna, or bad (shorted or improperly terminated) coax.

Paige
 
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