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TranSystem AIDC - Another noise story



Another email about TranSystem converter noise figure!

I did take some more measurements and came up with a new modification since
this topic is of such interest.  Thanks go to Mark, N0NSV, for sending me
his TranSystem converter to work with.  He will get it back working much
better.

I used a sensitivity measurement method with a signal source and spectrum
analyzer with Noise Marker capability.  The advantage is that I did not have
to guess at how to account for the noise contribution from the image
frequency... it is included in the measurement.  The HP8970A noise figure
meter does not automatically account for the image contribution.

The results, in a nutshell, are as follows:

With no mods => 9.8 dB NF !!
With stub removed => 4.1 dB NF (123 and 145 MHz IF)
With stub retuned to image frequency => 1.8 dB NF

I retuned the stub to notch the 2111 MHz image frequency by soldering a
0.5pf chip capacitor on the open end of the stub, shifting its frequency.

Details can be found at http://communities.msn.com/wc0y

73,
Ward - WC0Y

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