Comm Radio Reception Issue

fangzz · Post by **fangzz** » Fri Jan 18, 2013 10:26 pm

Wonder if any of you have ever experience this issue of radio reception degrading as your leg time increases, i.e., short hop, no problems; comm on the ground always seems fine; long leg, by the end of it, I can tell by the sidetone that xmit out is good, but I can't hear responses. Recently, an FBO told me after I landed and asked if he had heard my xmissions, "yeah, I answered you all four times." Never heard him. This from 20nm and closer. Recurring problem.

I've checked the antenna coax connections and they are clean. Antenna install looks good and tight. Radio is a newer Garmin sl40 w/ about 250 hours/ 3 years.

Thot I'd ask you guys before running to the local avionics shop. What this sounds like to me is static buildup during flight. You know, that stuff that those static wicks off the trailing edge of airliner wings are supposed to get rid of.

Ok, over to you guys. Drew

FredMa · Post by **FredMa** » Sat Jan 19, 2013 7:38 am

If static electricity were an issue I don't believe the problem would be unique to your 170. I would be inclined to think the problem is more along the lines of a heat build-up issue either with your radio or possibly wiring issues. Do you have a circuit breaker supplying power to your radio or is it an AGS fuse holder? Have you tried turning your radio off for a few minutes then back on after it has cooled down to see if it works again?

Post by **Bruce Fenstermacher** » Sat Jan 19, 2013 1:02 pm

I think Fred has nailed it. It is likely a heat build up issue in the radio. Avionics guys who know electronics could probably tell you exactly what is likely wrong. Avonics part changers will just know how to change the radio out with another.

fangzz · Post by **fangzz** » Mon Jan 21, 2013 4:09 pm

Thanks for that Fred and Bruce. Had NOT thought of that since the radio is virtually new and of the micro-cirquitry generation and thus almost no heat generation. Or so I think/thought. Your idea is a really good one to determine if that is what's going on. I have a longish x-country coming up this week and I'm going to try it with the same FBO that heard me, but I couldn't hear. If that's the issue, I guess I'll have to install some sort of small rack cooling fan (?). The wiring has been worked over fairly recently when I had the master switch replaced and all fuzes replaced with cb's. And this problem has persisted through all of that. Only happens on a longish trip. Really bit me this fall on my flight from Wa state to Florida. Lost all comm going into Helena class D. Had to use the handheld. Inconvenient. Then, on the ground, all returned to 'normal.' Thanks for the tip, and I'll sure report back by end of this week. Drew

Post by **GAHorn** » Tue Jan 22, 2013 3:35 pm

Your "sidetone" clarity is not a valid test of your RF output (transmitter). Sidetone is taken from your mic-input.

Heat degredation is most likely occuring to a compnent, and while cooling air might delay the failure, it's likely only a matter of time before a hard failure occurs. I'd send it back to Garmin with an explanation and ask them to evaluate the radio. Chances are they'll fix it inexpensively (if not free.)

fangzz · Post by **fangzz** » Thu Jan 24, 2013 6:43 pm

Ok, guys, here's the 'get-back' on my issue and x-country tues thru wed (yesterday).

Garmin (Apollo) SL40. It sucks. I think it's getting worse, if that's possible.

I can talk to folks that are very close by, on the airport or in the pattern, especially right after turning it on. I believe I can say that the longer it operates, the worse it gets. And, I believe I'm being heard but not hearing the return, answering transmissions. Yesterday, coming back from Bham, I wasn't able to speak to any ground station. I tried FSS, Birmingham approach/departure, Montgomery app/dep, Eglin radar. Couldn't hear anyone. I cycled the radio off/on momentarily a couple times. Turned off for several minutes couple of times. No effect. Pretty disgusting.

'Heat' still could very well be the culprit. Just don't know at this point, but the on/off thing I tried sure seemed to have no effect whatever.

Garmin is a flat-rate $450 to open the shipping box and put it on the table. Goes up from there. I'm in line with the local (good) avionics shop. I'm up in about a month (glad his business is good!). Til then, I may as well be in a nordo cub. In the meantime, I'll try anything you guys think might lead to a fix, if you have any other ideas (the heat idea was a good one), and I'll see if I can find a slide in replacement as a test. That would probably need to be another SL 40.

Thanks in advance for your interest and inputs, past and future. Drew

bigrenna · Post by **bigrenna** » Thu Jan 24, 2013 7:17 pm

delete

c170b53 · Post by **c170b53** » Thu Jan 24, 2013 9:11 pm

I have a KY97 with a similar problem except mine is in the transmit circuit. One day after flying for awhile it began to act up and I couldn't tx. The period between on and act up got shorter. So I took it to the shop as I gave up using oscilloscopes long ago and expected then to locate the problem. Nope, the worst thing about an intermittent problem is fixing it can be expensive. So after $600 spent, it sits on my shelf gathering dust. I did open it up and because of the amount of surface mounted IC's, I'm thinking the manufacturers when presented with a repair job, just gut the innards, replace them with new and send them back as repaired.
I also had a Garmin transponder DOA and although I hadn't installed and used the unit under its warranty period, they still stood behind their product, so I'm likely to prefer their products over others.

170C · Post by **170C** » Thu Jan 24, 2013 9:30 pm

One thing regarding your turning the radio off for a short time and not getting any favorable results is that possibly you need to try leaving it off for an extended time, then try it again. The down time is anyone's guess, but were it mine, I would leave it off for 15 minutes or so. Another option would be to take off and fly for a period, then turn the radio on and see how long it works properly before failing. Hopefully you have or can borrow a hand held if you are at a controlled field. Just some thoughts.

fangzz · Post by **fangzz** » Thu Jan 24, 2013 9:50 pm

Thanks a bunch guys.

Good idea, Pokey. Also, Bigs, I like that thot of the coax. I've only checked that to the extent of looking inside the coax to antenna connection for corrosion, etc. Clean as a whistle. But, I think it's simple and cheap enuf to build a new coax and running it directly from the antenna to the radio (not thru the post, etc....) and see what happens. If that does no good, I have found a close av shop that is willing to just hook 'er up on the bench and check what they can. Probably step two. I'm on it tomorrow, so I'll keep you posted. Keep those cards and letters coming. If that coax works, I'm buying you dinner, Bigs! Drew

blueldr · Post by **blueldr** » Thu Jan 24, 2013 11:41 pm

If I had a radio that the manufacturers repair department wanted that kind of money to look at it, it would be gone right now if not sooner. I had such repetative problems with a King radio that I dumped it after the second $375 repair. It was a comm/nav but if I happen to want VOR information, I can get better accuracy and distance too with my GPS.
I replaced it with the least expensive radio I've ever seen and had PERFECT service out of it for about fifteen years. It's a VAL COM 760 TSO. Best radio I ever owned, and sold new for about $695.

hilltop170 · Post by **hilltop170** » Thu Jan 24, 2013 11:49 pm

If heat is part of the problem, is the heat being generated by the SL40 or is it maybe mounted above a hot transponder or other hot radio? I know the Garmin 430/530 GPS run hot and they don't seem to care, not sure about the SL40. I have never had a problem with a Garmin since 1990, ever.

fangzz · Post by **fangzz** » Fri Jan 25, 2013 1:23 am

YGTBSM!! Blu -- In 09, when we bot this little beauty, we installed a new radio and xponder -- just so's everything would be perfect, right? Guess what we replaced with the Garmin -- Val 760. Still have it. NOTHING but problems with this radio. Day ONE. Sorry to shout. Never know when folks will hear -- or not. Oh well. 5k later. I'm encouraged by the idea of a coax experiment.

The radio sits right on top of the xponder. Radio very strong on initial turn on. Makes it sound like heat, don't it?? We'll see. That includes drinks, BTW Bigs. Drew

N2255D · Post by **N2255D** » Fri Jan 25, 2013 1:43 am

I've got a VAL 760 also. Was in the plane when got it in 1996. Went blank this spring. Fuse checked good but found a wire on the fuse holder broken. Repaired the wire and been workin good ever since. My other radio is a Bendix/King GPS/Comm installed early 1997. The 5 year internal battery died after 10 years and it's been working great ever since replacement.

hilltop170 · Post by **hilltop170** » Fri Jan 25, 2013 3:11 am

fangzz wrote: The radio sits right on top of the xponder. Radio very strong on initial turn on. Makes it sound like heat, don't it??

Try a flight with the transponder turned off and see if the problem repeats. If it does, can you move the SL40 under the transponder? That might take care of it.

The International Cessna 170 Association