[ARC5] Lopsided modulation

[Kenneth G. Gordon]

On 26 Feb 2018 at 14:40, AKLDGUY . wrote:

> net. I wondered why this is peculiar to the Command transmitters.

I am betting it is. I have to get one or more of my hacked-up "ARC-5" transmitters in 
operation one of these days. TCK-4 first though....

> I am unwilling to add a buffer stage between the VFO and PA as the
> transmitter is absolutely stock unmodified. 

Good on ya. I wouldn't either.

> The best I can hope to do is regulate the VFO B+ in case FM is being
> introduced via unsuppressed audio on the main dynamotor (550V) line. 

That is a good thought...but voltage regulation of the oscillator may not help much.

> As I mentioned earlier, the MD7 modulator schematic shows only a small
> decoupling capacitor (C55 = 1.2 uF) at the dynamotor output, and there
> is no further decoupling. C57 (0.05 uF doesn't count, it's only a
> spike suppressor). I followed this decoupling arrangement in my
> homebrew modulator, and more microfarads may be necessary. 

Well, remember to be somewhat careful there: that value, 1.2 uFd, may have been chosen 
by the original designers for a good reason. We might wish to check that out.

However, in the meantime, I think by increaseing that value significantly higher, you could, 
at least, determine if that is an important factor.

Ken W7EKB

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