The International Cessna 170 Association

pgr380 · Post by **pgr380** » Sun Jul 27, 2003 1:24 am

I have a 170B with a Mark 12 and built in intercom (no audio panel). Intercom and handheld mic work fine, but I cannot get a transmission with the PTT (an add-on type). There are 3 jacks for the headset - mic, phone & PTT. I can pick up a carrier when the PTT is keyed, but no transmission. Any ideas?

Post by **GAHorn** » Sun Jul 27, 2003 6:20 pm

Your PTT (add on unit) should plug into your regular hand-mic jack, then your headset (aviation types only) should plug into your PTT jack. All the PTT does is insert a hand-held mic transmit switch into the circuit. If your units are in good condition, and if your headset mic is compatible with your radio, then it should work flawlessly. Otherwise, it sounds like you need to make a trip to the local avionics shop.

Roesbery · Post by **Roesbery** » Mon Jul 28, 2003 1:34 am

Don't know if your situation is the same or not..... But some time back I installed a radio with the intercom feature and added a mic jack on the copilot side. When I ordered the extra ptt switch the avionics shop said that it needed to be the correct switch to match the radio and intercom use and they sent the "correct one" ........ As it turned out my old ptt worked fine, but not the new one, did some checking with a little multi meter and found that the two were wired differently. So changed the wires on the new one to match the old one and it has worked fine since. You might borrow one or more ptt switches and see if any work and if they do either get a new switch that matches or rewire yours to match one that works. Or take it to a avionics shop and save the agrivation if it's not too inconvenient.

pgr380 · Post by **pgr380** » Mon Jul 28, 2003 1:55 am

Thanks for the replies. As it turns out, the only trial and error combination I didn't try is the one that works. Evidently, the PTT jack is wired differently than what I've seen before. As I indicated, there

are three jacks available - phone, mic and PTT. The trick is to not use the adapter on the PTT unit. In other words, the headphones plug into their regular jacks, and the PTT plugs into its own separate jack. The handheld mic stays in place in its jack. Key the PTT, and the mic on the headset works fine.
Thanks for the quick resonses.