[AMRadio] Frequency Response

Donald Chester k4kyv at hotmail.com
Sun Sep 26 13:44:02 EDT 2004

>I have always admired what Don has done with his modulation system. That 
>3400 hertz brick wall filter is a rarity unless one uses high technology 
>active circuitry such as active op-amps, switched capacitor filters, dsp, 
>etc.  I believe Don has a passive module that does a great job. I wonder 
>where he got it?

It is a passive module.  I picked it up in Washington, DC back in 1972 when 
I had stopped over there to visit a friend.  We went to a little 
hole-in-the-wall military surplus outlet.  I paid $5 for it.  It is potted, 
about 1 1/2" X 1 3/4" X 2 ".  It has an octal plug on the bottom.  The 
impedance in/out is 10,000 ohms.  I wasn't sure about it when I purchased 
it, but when I tried it out with a signal generator after returning home, I 
wished I had bought every one they had.  It is flat up to about 3300~, and 
at 3500~ the signal is so far down as to be undetectable on the scope.  You 
can simulate the envelope pattern of a cw signal by swishing the test 
oscillator about 100~!

The only thing like that I have ever seen at a hamfest was physically and 
electrically identical but had a useless cutoff frequency of 2000~.


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