[Elecraft] K3 Low Power FM

[Dave & Jeanne Robertson]

Thanks Lyle,
 I removed all my filters and installed the 2.7 k filter in port 1 (in place 
of the FM filter). after reconfiguring the K3 the rig worked very well with 
SSB and CW so the RF board is good. The only thing I need to do is get a 
working FM filter from Elecraft.  Right now I got a .001 capacitor in the 
place of the FM filter and this gives me the ability to at least work FM 
until I can get the situation fixed.
I have some equipment that can generate a signal but I have to read up on 
the AFV function. Then I will reinstall the FM filter and try your tests I 
think I will know what I will find because with the capacitor in place of 
the FM filter lets me output any power I ask for.

Thanks again for your good advice and 73
Dave KD1NA


----- Original Message ----- 
From: "Lyle Johnson" <kk7p at wavecable.com>
To: "Dave & Jeanne Robertson" <darjar at comcast.net>
Cc: "Elecraft" <elecraft at mailman.qth.net>
Sent: Sunday, May 25, 2008 10:23 PM
Subject: Re: [Elecraft] K3 Low Power FM


>> 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
>