Batboard

I have a VHF MCS2000 with a Type 2 head.

The radio works well but I've noticed some internally generated low level QRM which varies in intensity on different frequencies.

I used an AM receiver tuned to the same frequencies and can hear the QRM particularily around the external speaker wiring and on the antenna coaxial cable. The QRM disappears when I power down the MCS2000. It seems to be worse on certain frequencies and is only noticeable on very weak signals - its sounds like a rapid pulse - like an engine ticking over.

I am using a linear PSU - so no switch mode QRM.

I guess its radiating down the coaxial cable and into the antenna - or maybe from the speaker wiring ??

The external speaker wiring is still in its original "tied together" state.

Has anybody else heard this pulse type interference on weak signals on certain frequencies?

Maybe a ferrite core around the speaker wiring might help? Or a ferrite clip on the coaxial cable?

Any thoughts?

Not sure if this is the problem, but could the radio be going in and out of VCO lock? Is the radio scanning when this happens? Do you have any out of band channels in a scan list? Out if lock could radiate out any part of the radio, those are my thoughts.

The MCS2000 is not scanning when I hear the QRM.

Its worse on certain frequencies - I guess its processor noise.

I have set the SQ very low for DX - on very weak signals the "noise" masks the internal QRM and on strong signals the signal masks the QRM You only really hear it on medium weak signals.

I guess you get sproggies/birdies on all radios. As the QRM is worse on a local chat freq , I notice it more.

I'd be interested if anybody else with a VHF MCS2000 notice any QRM - you can check it better with an AM scanner. Maybe its poor grounding somewhere - but my MCS2000 is in mint condition. I can hear it worse with an AM scanner around the speaker wiring. As I tune across 2m on AM (not FM) , the QRM varies in intensity.

I have disabled RX pre-emphasis - I think the audio sounds brighter ...but maybe that makes the internal QRM sound worse? Pre-emphasis enabled on RX might "attenuate" the internal QRM?