[Elecraft] K3 Low Power FM

[Lyle Johnson]

> With all filter in place and with several checks on configuration and reloading the radio's firmware I had no success in getting out any more then 2 watts out max on FM.
> 
> I removed the FM filter and replaced it with a .001 UF capacitor. I was successful in putting out any amount of power I selected on FM. I monitored the transmittion and it produces a very clean FM signal. So either there is something wrong with the filter or RF Board.
> 
> Any comments (constructive please).

1) Move an SSB filter to position #1 and see if Tx/Rx is nominal.  This 
will tell you if the RF board is OK.

2) If it is, put the SSB filter back and re-install the FM filter.

3) If you have a sig gen or source of very stable amplitude signal, turn 
AGC off and use the AFV function and record the level in SSB mode coming 
through the SSB filter.  Signal needs to have a good S/N but not be more 
than S9+5 or so to be sure hardware AGC doesn't interfere with the 
measurement.

4) advance to the dBV position on the VFO B display and you'll see it 
bobbling around +/- 0.1 or 0.2 dB.

5) Enable the FM filter for SSB and then tap XFIL to switch to the FM 
filter.  You'll then see the relative attenuation of that filter vs your 
SSB filter.

In my case, the 2.8kHz, 6.0 kHz and 13.0 kHz filters are all within a 
tiny fraction of a dB of each other at an audio pitch of several hundred 
Hz and a good S/N .  Sig Gen was at -80 dBm, or 22 uV.

---

The AFV and dBV function of the K3 makes it possible to do some pretty 
accurate measurements.  You can determine MDS, see filter attenuation 
and be sure your filter configuration loss compensation values are in 
fact correct instead of guessing, etc.


73,

Lyle KK7P