Strange radio problem

[redcar92@hotmail.c]

I have a problem with several symptoms. When I try to xmit on the pilot or passenger plugs my signal is garbled.  With the engine off I receive OK but with the engine running over 1k rpm there is terrible static. If I unplug the mic cable the static goes away. This happens with both the pilot and passenger connections. I removed the connectors from the panel to eliminate possible ground loop but no joy. I have two headsets and both display the same symptoms.  Any suggestions please.
Regards, Bill

 

[Raymo]

Bill,

What kind of engine and ignition do you have?
Are the plug wires shielded?
Are the P-leads properly shielded?

 

[redcar92@hotmail.c]

Ray, thanks for the response. My plane is a Zenith CH750 Cruzer with a UL Power 350is engine and electronic ignition. Every things stock, so I don't thing plug wires are shielded. Not sure what P-leads are but there are no ground loops from the mic and phone plugs.   

 

[Raymo]

No magnetos means no P-leads to worry about, Bill.

Does the interference change with engine RPM above 1000? In other words, does it seem related to engine RPM?

1000 RPM is also likely to be when your alternator starts putting out more voltage. Can you isolate it from the system?

Once you know the source of the noise, it is easier to troubleshoot.

 

[redcar92@hotmail.c]

I will try to isolate the alternator when the rain stops here. Another symptom is that whenever I try to transmit I am totally unreadable, only one or two syllables in a short sentence,  with or with out engine running. I have replaced coax ends and checked coax with a meter.
Bill

 

[Raymo]

Have you tried a different headset?

Something else to confirm is that the shield of shielded wires are grounded only on one end.

 

[redcar92@hotmail.c]

I have 2 headsets and a handheld radio I use for trouble shooting. I can transmit from airplane and listen to handheld. The mic plugs are grounded at plug end and back at pin 1 to intercom. The phone plug is grounded at pin 1 only. I have removed all 4 connectors from panel and still have problem.
Bill

 

[redcar92@hotmail.c]

I think I have found my xmit problem. I had coiled 2 loops of coax. Once I straitened the coax out my garbled xmit seems to have stopped. I was not able to start motor today. Will try tomorrow.
Bill

 

[jakej]

Do you have RG58 or RG400 coax ?

 

[redcar92@hotmail.c]

I have RG58.

 

[jakej]

There lies the problem - I would never use RG58, modern avionics require a much better coax like RG400. RG58 is not allowed to be used in new installations in certified aircraft either so I would not use it in 'experimental' aircraft for the same reasons as the certified market .

 

[redcar92@hotmail.c]

I was able to start the engine and taxi a bit plus some runups. The radio worked exactly as expected. I think my problem is solved. Thanks everyone for your contributions.