[CQ-Contest] Fwd: [FCG] riding the RF gain...

Tree N6TR tree at kkn.net
Thu Dec 6 12:35:34 EST 2001

Sorry for the confusion generated by my post.

When I said "in band" I was thinking "in passband" as opposed
to signals within the amateur band.

Actually, I consider the "in band" IMD performance of most 
receivers today to be really disappointing.  I think that when 
you have lots of noise, this distortion makes it really hard 
to copy signals near the noise level.  It might also explain 
why some receivers sound bad when there is a big pileup.

The IMD graphs show two signals mixing - but that isn't real 
life all of the time!

Backing off the RF gain quickly attenuates these products by 
another 20 or 25 db.

You can see a graph of this IMD distortion at this URL:
http://www.arrl.org/tis/info/pdf/k2.pdf on page 19 under the
title "In-Band Receiver IMD Graphs".  The K2 actually looks
about 10 db better than my TS850 and some other radios I have
looked at (including the MP).  Perhaps this helps explain why
some people think this receiver responds to pileups better.

I did some work with AC6T to try and get better results with
the 850, but we weren't able to come up with anything after
about a month of work.

You can make your own measurements if you are interested.  You
will need two XTAL oscillators about a few hundred Hz apart
with pretty much the same output.  You can download software
to use with a soundcard to turn your PC into a spectrum analyzer.
Then, you can play with your AGC and RF gain settings to see the

Ask anyone who has a direct conversion receiver to bring it
over - and you will be amazed at the difference!!

73 Tree  N6TR
tree at contesting.com

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