[ARC5] Chirp in Command Set transmitters.

[David Stinson]

Jim Mandaville wrote:
>... came across a "hint" for eliminating chirp in command transmitters.
> This guy says his was caused by RF getting on the heater wiring and that
> shielding and bypassing that wiring and adding a ground strap across the
> chassis solved his chirp problem and that of others he told this to.

I've never done this, nor needed to do it.  This gentleman's problem
likely had its roots in the near universal mistuning of the 
output of the command transmitters, or in the attempt to use
them with an end-fed wire without being in a bonded-to-ground
transmitter rack, as designed.  Either could have caused RF 
to show up in his power supplies.  

I recommend a coax fed antenna.  In order to properly match 
this, you can connect a 4:1 UNUN toroid transformer between
the antenna post and the coax.  A cheap-n-easy way is to 
put a high quality capacitor of around 50 PF in series 
between the antenna post and the coax center conductor
(75 PF if on 80 meters).
The cap must be rated at least 1 KV; 2 KV is better.
It also must be NP0 rated so it doesn't drift with heating.
Thermal drift will cause chirp. 
This is quick, cheap and it works, but the UNUN is better.
Kudos to Mike Hanz for that solution.

73 Dave S. AB5S