BMW R1200RT/R1250RT Forum

Hello, not sure which section this should be in.
I have a problem with very loud "channel" noise - the hiss you hear when you are listening on a radio and someone else opens the channel to transmit.
I'm running Autocom Pro Avi comms units (2 bikes) with PMR radios. Rider to pillion no problems. Rirder to rider using barrery eliminator from bike battery - very loud channel noise, enough to drown out speech. When I use separate radio battery it's fine.
Spoke with Autocom, can't really help as they only supply battery eliminators for selected Kenwood radios. Tried their power filter supply to the autocom units, still noisey. Tried the filters on the radio battery eliminators, no change.
Reverted back to radio battery perfect.
Any ideas from any learned radio experts?
Radio batteries are a pain even though they last a couple of days. It's just the hassle getting them out from under the seats.
Thanks in anticipation.

Are you using isolated audio cables between the radio and autocom unit?

I suggest that you give Sam Wray at Chainspeed a call - do tell him I referred you.  You will need to describe all the wiring and tell him what radios you are using.


Hope this helps,


John Bentall

Thnaks for your replies.
Graham, I'm using a separate power feed for the radios. I'm now going to try using the old Kenwood battery eliminator as the power supply.
Beemerboy, Ill give chainspeed a ring before I start "playing" with other supplies.
Thanks again guys

Its not the power that is the problem I think, because both units are powered from the bike when you connect the audio cable from the radio to the autocom you will set up a ground loop so neither unit can have a fixed known reference ground, to overcome this an isolation transformer needs to be fitted on the audio line between the radio and the autocom.

Graham, thanks,
That's presumably what the Autocomm lead does when I use their battery eliminator.
Still working on it.
SWMBO has just bought a new bike so I'm now in the process of stripping out tyhe autocom, satnav and Innovv camera.
No peace for the wicked,

Humble apologies, I thought the 'battery eliminator' was a filter that just stripped out ignition noise from the supply (You have one of those also I presume?). Just googled it and you're correct so ignore everything I've said. It could always be faulty however.