Message	Date	From	Subject
6834	2011-11-16 21:20:56	Ross Tucker	Front panel hookup ground loop?
Dear all, I am preparing the chassis for a 40-m transceiver (kd1jv's mmr40) and am curious as to best practices in wiring front panel. Specifically, I am attempting to gather all of the microphone/push button/switches into one wiring harness so I can disconnect main board easily for testing. How should I hook up each connector's ground? Do I need to worry about ground loop problems for microphone connector, etc. or can I just wire everything serially/point-to-point? Thanks for your input, Ross, NS7F
6836	2011-11-17 05:27:07	Dan Mills	Re: Front panel hookup ground loop?
On Wed, 2011-11-16 at 22:20 -0700, Ross Tucker wrote: > Dear all, > > I am preparing the chassis for a 40-m transceiver (kd1jv's mmr40) and > am curious as to best practices in wiring front panel. Specifically, I > am attempting to gather all of the microphone/push button/switches > into one wiring harness so I can disconnect main board easily for > testing. Microphone level audio is tricky, and should travel on its own screened cable. More generally, you need to be aware that all the external wiring (PTT, Mic, Mic power, Speaker, Headphones, Key, CAT?.....) are potential ways for RF to get back into the radio. Inductors are good, opto isolation of digital inputs right at the input is better. Switching inputs going directly to control logic pins are the kiss of death. The ideal case is actually to provide a balanced microphone input, in which case the screen should go directly to chassis as close to the connector as possible, the differential pair can then run via a common mode choke to the mic amp. Regards, Dan.

On Wed, 2011-11-16 at 22:20 -0700, Ross Tucker wrote:

> Dear all,
>
> I am preparing the chassis for a 40-m transceiver (kd1jv's mmr40) and
> am curious as to best practices in wiring front panel. Specifically, I
> am attempting to gather all of the microphone/push button/switches
> into one wiring harness so I can disconnect main board easily for
> testing.

Microphone level audio is tricky, and should travel on its own screened
cable.

More generally, you need to be aware that all the external wiring (PTT,
Mic, Mic power, Speaker, Headphones, Key, CAT?.....) are potential ways
for RF to get back into the radio. Inductors are good, opto isolation of
digital inputs right at the input is better.
Switching inputs going directly to control logic pins are the kiss of
death.

The ideal case is actually to provide a balanced microphone input, in
which case the screen should go directly to chassis as close to the
connector as possible, the differential pair can then run via a common
mode choke to the mic amp.

Regards, Dan.