Alinco: Alinco DR638 Microphonics on UHF

[N9JIG]

I have a DR635 installed in my vehicle and use it for ham, GMRS and rail monitoring. For the last 6 or 7 years it has worked just fine.

Lately I noticed howling at high volume levels on our GMRS repeater when that is in the main band. When the same channel is in the sub band the howling goes away.

I don't get this howling on other channels, like rail channels, on either the main or sub bands.

I do have an external speaker next to the radio, could this be causing it?

 

[RFI-EMI-GUY]

I am not familiar with that radio, but in general it could be loose shields or components in the VCO and PLL sections. Open it up and tap around the circuitry while you have a full quieted signal into the receiver. Yes the speaker is part of the equation but if it was there all along, something is loose.

 

[cmdrwill]

something is loose

Could loose screws that hold the circuit board(s) to the frame. Or loose shield(s).

 

[buddrousa]

I had a dual band alinco that was phonic never did get it out of it.

 

[N9JIG]

Well, I found something interesting that hams like me should know but never do:

READ THE FLIPPING MANUAL!

There are two external speaker jacks on the rear panel, one marked "SP" and the other "ST". I had assumed that this allowed one to use on for the main and the other for the sub band.

NO, NO, NO.

The one marked "ST" is for a stereo plug to be wired for two speakers, the jack marked "SP" is for a mono plug for a single external speaker. I had two mono speakers plugged into these jacks.

I will need to get or make an adapter to convert a 3-wire stereo plug into two mono 2-wire jacks. Until I do I will live with one speaker and no howling.

This is properly described in the manual but we never read these, do we?

Rich Carlson, N9IDIOT
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[hill]

The DR635 is a ham radio that is made just to transmit on the ham bands. Did you modify it to transmit outside these limits. If it has been modified it could be anything with the radio only guaranteed with the ham bands.

 

[N9JIG]

That is my second mistake. It is actually a DR-638, which is nominally Part 90 certified. I used to have a 635 that my 638 replaced and confused them as they are pretty similar in appearance. It has not been modified.