|[AMRadio] Frequency Response|
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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