---------------------------------------------------------- Avionics-List Digest Archive --- Total Messages Posted Mon 09/28/09: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 08:54 PM - Re: Transmit troubles on comm radios (Noel Loveys) ________________________________ Message 1 _____________________________________ Time: 08:54:58 PM PST US From: "Noel Loveys" Subject: RE: Avionics-List: Transmit troubles on comm radios Just noticed the part where you say others in the pattern say you are breaking up. This puts the problem squarely in your PTT circuit. Most transmitters have a pin ground out to cause the transceiver to go into transmit mode. In your case That ground is dirty or loose. Check your pin out for the PTT and then check the appropriate circuitry. BUT FIRST.... Before you go pulling everything out I would recommend trying a different microphone if you are using one with the PTT on the mic or a different PTT switch which you would use for headsets. Dollare will get you doughnuts the problem is a dirty PTT switch. Noel -----Original Message----- From: owner-avionics-list-server@matronics.com [mailto:owner-avionics-list-server@matronics.com] On Behalf Of Ron Raby Sent: Tuesday, September 22, 2009 1:07 PM Subject: Re: Avionics-List: Transmit troubles on comm radios Dean I had a very similar problem. It turned out to be a poorly crimped pin on a purchased harness. Try inspecting at all the related connectors and pins. Ron Raby Lancair ES ----- Original Message ----- From: "Dave Lammers" Sent: Tuesday, September 22, 2009 9:33 AM Subject: Re: Avionics-List: Transmit troubles on comm radios > > It might be as simple as a poor ground from the PTT switch to ground > Regards, > Dave Lammers > > DEAN PSIROPOULOS wrote: >> >> >> >> Hi all: >> >> Maybe you can help with my transmit problems. I have a UPS Aviation >> Technologies (now Garmin AT) radio stack with SL-30 Nav Comm, GX-65 >> GPS/Comm, SL-70 transponder and SL-10MS audio panel (actually a PS-6000 >> with >> UPS AT nameplate). I checked out everything according to the >> installation >> manuals while the airplane was sitting on the ramp and the engine NOT >> running. Now that I've been flying a lot, I'm getting a crackling in the >> sidetone and when I look at the "TX" light on the radio it's flickering >> as >> if someone were pulsing the press-to-talk switch 4-5 times per second, >> even >> though I'm holding the PTT down tight. This happens on both radios and >> people in the pattern say I'm breaking up and garbled. I've tried several >> things looking for a solution, they are: >> >> 1) Turn down the MIC gains on both radios (in steps, a little at a time, >> over several flights). In the end I had them turned down so much I >> couldn't >> get a side tone in the earphones and suspect no-one could hear me at all. >> >> 2) I tried a couple different headsets (inexpensive non ANR types, >> Sigtronics and Pilot Avionics units, both around 15 years old but well >> taken >> care of and worked just fine in the Cessnas I used to rent). No joy. >> >> 3) I tried both headsets with and without foam muffs over the >> microphones. >> No difference that I could tell with or without the muffs. >> >> 4) Placed ferrite beads over both coax lines running to the transmit >> antennas (about 3/4 of the way down to the antennas, don't have access to >> the base of the antennas right now, but will when I remove the floor >> panels >> for annual inspection). No help! >> >> 5) Shut off the field in my B&C LR-60 alternator (with external >> regulator) >> to operate on battery only. No change (I'm using forest of ground tabs >> ala >> AEC philosophy and I'm NOT getting alternator noise in the reception of >> either radio so I didn't expect this to help but it was easy to test). >> >> 6)Since I used fine (24 gauge 5 condutor MAC servo cable, no shielding) >> wire >> to take the PTT signal from the PTT on the control stick to the pilots >> mic >> jack, I thought maybe that was causing a problem so I tried using the >> passengers PTT (wired with 22 ga shielded tefzel) instead of the pilots. >> No >> change. >> >> 7) The audio panel has a built in fail-safe feature that routes the PTT >> and >> mic/earphone signals direct to the number 1 NAV/COM in the event of audio >> panel failure. I shut off the audio panel and tried that. The NAV/COMM >> TX >> light comes on but still flickers and is crackly so it's not that. I of >> course could not test the #2 radio this way but would expect it to be the >> same. >> Transmit antenna location is under the belly of the airplane (all metal >> RV-6A). Two Comant bent whips about 40 inches apart just aft of the wing >> spar. >> >> The GPS portion of the GX-60 and VOR/ILS portion of the SL-30 work just >> fine. Comm. reception on both radios is loud and clear (at least I can >> hear >> people in the pattern even if I can't talk to them). >> >> When I originally ran through the installation checkout I left the >> settings >> on the radios at the factory recommended (transmit worked fine so I left >> the >> settings alone) and have been making changes to the Mic gains only. >> These >> are computer controlled radios so I'm wondering if I need to adjust any >> other parameters such as squelch (no pots to control squelch like the old >> days) after making the Mic gain adjustments. Could the two be somehow >> related through logic in the computer program that runs the radios? >> I'm really stumped, any suggestions? Any UPS AT radio stack users have >> this >> problem? How did you fix it? Should I run through the installation >> checkout >> with the engine running so as to have more noise impinging on the >> microphone >> while making adjustments? Don't like the idea of head down in the >> cockpit >> with engine running but I can tie down the airplane while doing the >> checks >> (I'm talking ground running here not trying to make adjustments in >> flight)! >> Thanks for the help. >> >> Dean Psiropoulos >> RV-6A N197DM >> Flying and tweeking. >> >> >> >> >> >> >> > > > ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message avionics-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Avionics-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/avionics-list Browse Digests http://www.matronics.com/digest/avionics-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.