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Scimitar · 7th Jan 2019, 2:49 pm

I am struggling a bit with an interface to connect the Yaesu FT-10SR to my Starcom Digital intercom unit on the bike. I have wired it as per the advice I have found so far, but have a ground loop. This is causing a loud alternator whine on the transmitted audio and just background whine on receive.
With testing that I have done so far, I need to isolate the two devices and preliminary tests with a pair of audio transformers worked to deal with the noise.

The issue I have is working out how to trigger the PTT. This works by grounding the two 390K resistors connected to data lines. My idea is to use an opto isolator there as we are only talking picoAmps. The LED in the opto needs to be driven from the Starcom which has no separate PTT output but uses the "single line" method of control. Starcom have been asked for their advice but are unable to disclose the circuit diagram of it. It is clear however that the Starcom must have its own PTT input enabled before any audio will be passed to the RADIO interface connector.

I am still not sure how I can sense the Starcom going into TX mode. Diagrams attached.

Looks like this chap has similar troubles... https://www.st-owners.com/forums/thr...terface.44939/

7th Jan 2019, 2:49 pm	#1
Scimitar Heptode Join Date: Oct 2015 Location: Gloucestershire, UK. Posts: 720	Amateur radio interfacing I am struggling a bit with an interface to connect the Yaesu FT-10SR to my Starcom Digital intercom unit on the bike. I have wired it as per the advice I have found so far, but have a ground loop. This is causing a loud alternator whine on the transmitted audio and just background whine on receive. With testing that I have done so far, I need to isolate the two devices and preliminary tests with a pair of audio transformers worked to deal with the noise. The issue I have is working out how to trigger the PTT. This works by grounding the two 390K resistors connected to data lines. My idea is to use an opto isolator there as we are only talking picoAmps. The LED in the opto needs to be driven from the Starcom which has no separate PTT output but uses the "single line" method of control. Starcom have been asked for their advice but are unable to disclose the circuit diagram of it. It is clear however that the Starcom must have its own PTT input enabled before any audio will be passed to the RADIO interface connector. I am still not sure how I can sense the Starcom going into TX mode. Diagrams attached. Looks like this chap has similar troubles... https://www.st-owners.com/forums/thr...terface.44939/ Attached Thumbnails Last edited by Scimitar; 7th Jan 2019 at 2:56 pm.