10m Birdie

[W4FMS]

"----In order to get a match at 28019 kHz as has been reported, the KPA100
oscillator has to be shifted to 18434.1 ----"

Hi also have the 28029 birdie.  I've also got the much stronger 28262
birdie.

I've wanted to eliminate this for some time since there a lot of cw activity
between 28025 and 28025.  My KPA100 is installed on the K2.  The birdie
produces about 1 s unit bar with the pre-amp on.  Based on Sverre comments,
how do I eliminate the birdie?  Is it merely the freq of the 18 MHz
oscillator.

Frank, W4FMS



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[Sverre Holm]

-----Original Message From: [hidden email] -----------
I've wanted to eliminate this for some time since there a lot of cw activity
between 28025 and 28025.  My KPA100 is installed on the K2.  The birdie
produces about 1 s unit bar with the pre-amp on.  Based on Sverre comments,
how do I eliminate the birdie?  Is it merely the freq of the 18 MHz
oscillator.
--------------------------------------------------------------

One solution is to shift the 18432 oscillator on the KPA100 to a frequency
above the 10m band. The oscillator is only used in a DC-DC converter for
producing a voltage for biasing the T/R-switch diodes and the RS232
interface, so the frequency is not critical at all. The only limitation is
that the 2N3904 - FT37-61 oscillator may get into trouble as frequency
increases. I have a half-built KPA100 so I cannot yet listen for birdies,
but I made some tests with two crystals from my junk box:

1. 38.45 MHz: oscillates, but only produces 42 Volts instead of 130 Volts
bias voltage
2. 40.00 MHz: oscillates at 1/3 frequency.

So it seems as if the oscillator circuit oscillates with less efficiency,
perhaps a transistor with a higher fT is required?
 
73

Sverre
LA3ZA
http://www.qsl.net/la3za/
 

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