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Radio noise and high amp draw on transmit

W

webstarr

Member
Hey everyone, happy to report I got my RV12 up and running again. Was having an issue with it not charging the battery but we found the loose connection and the charging issue is resolved.

The next issue I'm trying to solve is that I've been having some issues with radio transmission on the SL40. When I key the mic the side tone in my headset is really garbled and the amps on the Dynon start skyrocketing until I get a critical current warning.

Apparently the person on the receiving end can hear the transmission ok but I can't hear myself clearly at all. For now I've been using a handheld to transmit since I can receive just fine through the headset.

Any ideas on where I could start with troubleshooting this?

Thanks!
 
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The thin wires going to the amp-shunt are sensitive for induced magnetic field from the radio antenna coax wire when transmitting.
The voltage in the amp-shunt wires is typically 5-20 mV.
I would suggest using shielded wire and at least 2" from coax cable.
No experience with the SL40.
But there should be a possibility to change the side tone setting.

Good luck
 
I put a VOR/ILS in my 12. All the ohmmeter continuity checks were great, but I couldn’t get a signal. I replaced all the coax cable BNC connectors and it worked like a champ. Radio waves are fickle. They call it FM for a reason!😝
 
RFSchaller said:
I put a VOR/ILS in my 12. All the ohmmeter continuity checks were great, but I couldn’t get a signal. I replaced all the coax cable BNC connectors and it worked like a champ. Radio waves are fickle. They call it FM for a reason!😝
Click to expand...

DC and RF are very different - continuity checks can be very misleading.

As I have recommended before, all EAA chapters should get an antenna analyzer for their shared tool locker. They are not expensive and do far more than a simple SWR bridge. Builders should use this (or similar) on all antenna installations to verify proper operation.
https://www.dxengineering.com/parts/mfj-259d

Carl
 
Please define "skyrocketing amps"? Normal transmitting will use a few extra amps, maybe 3 or so.
 
Avanza said:
The thin wires going to the amp-shunt are sensitive for induced magnetic field from the radio antenna coax wire when transmitting.
The voltage in the amp-shunt wires is typically 5-20 mV.
I would suggest using shielded wire and at least 2" from coax cable.
No experience with the SL40.
But there should be a possibility to change the side tone setting.

Good luck
Click to expand...

Thank you for the reply. I will check the wiring and look into replacing it with shielded wiring if it's not already.
 
RFSchaller said:
I put a VOR/ILS in my 12. All the ohmmeter continuity checks were great, but I couldn’t get a signal. I replaced all the coax cable BNC connectors and it worked like a champ. Radio waves are fickle. They call it FM for a reason!😝
Click to expand...

Thank you for the reply. I'll look into replacing the connectors!
 
Carl Froehlich said:
DC and RF are very different - continuity checks can be very misleading.

As I have recommended before, all EAA chapters should get an antenna analyzer for their shared tool locker. They are not expensive and do far more than a simple SWR bridge. Builders should use this (or similar) on all antenna installations to verify proper operation.
https://www.dxengineering.com/parts/mfj-259d

Carl
Click to expand...

Thank you for the reply. I'll check and see if maybe our local avionics shop has one of these I could borrow...
 
Jpm757 said:
Please define "skyrocketing amps"? Normal transmitting will use a few extra amps, maybe 3 or so.
Click to expand...

Thank you for the reply.

By "skyrocketing amps" I mean when I hold down the PTT the amps just keep going up as long as I hold the button. Eventually they reach a value (50ish?) where the ammeter just shows a warning and the voice from my Dynon says "Critical Current!"
 
The high amp reading is almost certainly an artifact in the sensing circuit as previously posted. If your com was pulling 20 amps its CB or fuse would surely trip.
 
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