COM 2 transmits into CHT probes

[Michael Wellenzohn]

Hello,

when analyzing my EM Data I saw a couple short downwards spikes in my CHT and thanks to the feedback from Rob Hickman it hap end when I transmit with my COM 2.
The antenna is mounted on top behind the baggage area on the tail cone. I routed the RG-400 cable along the vertical baggage bulkhead channel F-1028.

I was just thinking if this vertical portion of the routing could be the issue. I will recheck antenna grounding and conductivity of the RG-400. When I transmit on COM 2 I hear some noise.
Did anyone with the same cable routing witnessed similar problems? I guess I just want to rule out that this could potentially contribute to the issue.

Regards
Michael

 

[BobTurner]

Yes, check the coax and antenna grounding, because it's easy to do. But I doubt that's the problem. Remember that the RF will go thru the fiberglass almost as if it wasn't there, so it has a pretty straight shot from the antenna right up to the front panel. The issue is the CHT thermocouples put out very small voltages, so even a tiny pickup is an issue. However, the CHT's change slowly, so the readout circuitry should filter out any RF. But it's never perfect. Do you have the CHT cables twisted together, in pairs? That will help.

 

[Bill.Peyton]

I would start by checking the integrity of the antenna. Disconnect the coax from the the back of the radio tray and check the VSWR. If you don't have the equipment, find a radio guy or a Ham. You can perform a simple check with an ohmmeter. Disconnect the coax from both ends and verify the center conductor continuity and that it is not shorted to the shield. Also verify the shield continuity. You should not have the sort of interference you are experiencing if the radio and the antenna are properly installed. The coax being in proximity of some of the wires should not present an issue. I have an. Antenna in the same location and the coax routed as you have, with no issues. You mention that the radio has noise, I assume during receive, that further indicates radio problems. You also specified that this happens only with com2, so I assume it does not with com1. If that is the case, then I would not necessarily be suspicious with your overall grounding scheme for the EMS, but would not rule it out depending on the outcome of your antenna tests.

 

[Michael Wellenzohn]

Thanks Bob and Bill.
Noise is only on COM2 when transmitting receiving is fine. COM 1 is not an issue regarding CHT probes. I'll check the coax next.

Regards
Michael