[Elecraft] 10M birdie and other assundries

[Geoffrey Mackenzie-Kennedy]

Hi Julius,

If the birdie at 28.019/20 MHz changes frequency when you change the 
transmitter power demand from <10w to >10w, then the KPA100's HV Bias 
oscillator is involved. Vic, K2VCO, and I had an off list discussion some 
time ago about birdies including this one, and though Vic found the birdie I 
did not because his HV Bias oscillator runs at 18.434 MHz while I have opted 
to keep mine at 16.293 MHz for reasons other than birdies. If I remember 
correctly this particular birdie involves not only the HV Bias oscillator 
but also another oscillator in the K2 which mix to produce a signal at a 
spurious response frequency of the receiver when tuned to 28.019 MHz. I'll 
have to look up my notes.

You can move this 10m birdie to another frequency by changing the HV Bias 
oscillator frequency although the options for all band freedom from birdies 
involving this source are limited. In my K2/100 the bias oscillator signal 
enters the K2 via the ribbon cable, which can be 'choked' with a clamp on 
ferrite, and the loudspeaker leads which can be removed from the KPA100 
board where the trace acts as a link, but be advised that these last two 
mods might not work with all K2/100s. Later on I repackaged the HV Bias 
oscillator and voltage multiplier in a shielded box, with pi configuration 
filters on all DC lines to kill the problem at source.

73,
Geoff
GM4ESD


----- Original Message ----- 
From: "J F" <phriendly1 at yahoo.com>
To: <elecraft at mailman.qth.net>
Sent: Tuesday, December 19, 2006 1:21 PM
Subject: [Elecraft] 10M birdie and other assundries


> Just out of curiousity, after spending some time on
> 10M during ARRL 10, I noticed a birdie around
> 28.019/20. Is there a way to eliminate this or move it
> below 28.000?

<snip>