Re: K3 Rx IMD

Posted by Ramiro Aceves on Nov 25, 2010; 10:36am
URL: http://elecraft.85.s1.nabble.com/Re-K3-Rx-IMD-tp5768777p5773711.html

Hi

I have tried to improve my IMD test setup. It is far from perfect, but I
have got rid of the broadcast station by bulding "quick and dirty " Xtal
4 MHz oscillator. It is built using a BC547 NPN bipolar transistor.

http://ea1abz.ure.es/XTAL.jpg

This is the beaufitul 4 MHz signal as received in the K3:

http://ea1abz.ure.es/xtal.png

As I do not have attenuatores nor combiners at the moment, the ugly
setup is:

http://ea1abz.ure.es/DDSandXTAL.jpg

50 cm wire conected at K3 antenna input.
4 MHz Xtal oscillador placed near the K3 wire antenna to produce a 9+20
signal.
DDS generator tuned 10 Hz over the Xtal frequency, same level as Xtal
signal.

Here is the graph AGC-OFF, AGC-S, AGC-F comparison. I reduced RF gain in
AGC-OFF mode to keep two tone audio signals level at the same value.
Aproximate measured 3rd order products, relative to one signal level is:

AGC-F: -17 dB
AGC-S: -23 dB
AGC-OFF: -45 dB.

http://ea1abz.ure.es/AGC-off_AGC-S_AGC-F.png


Let me know what do you think. This it what I can do with this poor
setup. In the future, I plan to build attenuators and hybrid combiner to
make a better test.

73, Ramiro. EA4NZ





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