[CA] [CA11] Clicking interference on VHF from L365 Fishfinder

[boaterdepth]

Hi, we bought a used boat that came with an L365 Fishfinder. According to paperwork on the boat, the L365 was purchased new in 2002. This old sounder still works fine for depth and water temperature but causes clicking interference in the VHF radio, mainly Channel 16. Here are my troubleshooting notes from the past few weeks of investigating:

The sounder (Raymarine L365 display unit) causes loud clicking interference in the wheelhouse VHF radio when the radio is tuned to channel 16 and to a much lesser extent to channel 72.
The clicks are more frequent as water depth shallows.
The interference was present with the old VHF radio and is the same with the new VHF radio.
The VHF radio is on the wheelhouse deckhead, about 4 feet from the sounder unit which is mounted at the helm.
The power wires for both units run together for part of their length to the helm electrical distribution box.
The sounder tranducer is on the transom and the the transducer wire is not running with the VHF power wires.
Two different handheld VHF radios detect the interference when held near the sounder and the interference diminishes as the handhelds are moved way from the sounder. The interference is gone when the handhelds are about 3 feet from the sounder.
I replaced the short antenna coax lead from the VHF radio to the VHF antenna on the wheelhouse roof -- no difference. The Antenna is about 6 feet from the sounder.
The interference is present whether the engine is running or not.

I think the source is the sounder (display) unit itself (not the transducer or transducer wire) but I don't know what to do. Some options maybe include:
- Some kind of shielding wiring for the L365?
- Buy a new Fishfinder?

Thanks for helping.

[Chuck - Raymarine - Moderator]

Welcome to the Raymarine Forum boaterdepth,

Please excuse the delay in this response. You may want to consider adding some RF chokes to the fishfinder's power cable. Please click here to view a FAQ addressing this subject. Should you not have done so already, is also recommended that you ensure that the RF drains / chassis grounds of the marine electronics have been addressed in the manner specified within the FAQ found here. Should this not address the issue, then it would be recommended that the fishfinder be replaced, as Raymarine's Product Repair Center can no longer service this retired fishfinder.