[ARC5] Modulation for ARC-5 transmitters.

[kgordon2006 at frontier.com]

On 8 Oct 2015 at 19:43, Dennis DuVall wrote:

> The circuits in the references are cathode modulators.

Well, yes....sort of. Actually, they are grid modulators, since what they are modulating is 
the grid bias voltage. The grid level is essentially fixed with regard to the plate, and the 
cathode is then varied above and (maybe even) below "ground". It is kinda weird, but 
does work very well.

> Both articles present the same circuit which works quite well but provides 
> only a limited amount of incidental "carrier control" action.

Neither one are any form of controlled-carrier modulation. I only included those to 
show Les how simple a fairly decent modulator could be.

>  Also, make sure only the cathode of the output amplifier tube(s) is 
> connected to the "key" jack before you try to use these circuits.  

When I used it, I simply plugged it into the key jack of my DX-35. In that transmitter, the 
oscillator, buffer and final are all cathode keyed. However, I was using a VFO, so that 
wasn't modulated or keyed.

> There are several schemes to achieve true carrier control, see many of the older editions of the ARRL handbook, CQ magazine
> articles, etc..

Yes. As I said, an earlier article in ER mag went into the method in some depth with 
working examples. I found that article to be very educational, and was the reason I 
decided to use it with my junk ARC-5 transmitters.

Due to the computer I am presently using (our oldest son's) I cannot search the index 
for the article in question, but will do so later.

Ken W7EKB