On Mon, 7 Apr 1997 03:28:39 -0400 (EDT) PGSPersEng@aol.com writes:
*** some stuff deleted ***
>
>I want to adjust the tuning range for the rig (get the low end with
>the
>DXers), and I've read the posts concerning it. However, would it make
>sense
>to simply replace D3 with a varactor? Anyway, can anybody tell me how
>much
>capacitance a 1N4004 is spec'd for?
>
>Thanks,
>Paul, AA1MI
>
>
>
Paul,
I went through a bag of 100 1N4004 diodes and measured the capacitance at
1 volt reverse bias. I had readings ranging from 20 pF to 44 pF (I did
not measure the capacitance ratio). It turns out that the 20 pF unit
gave the best tuning range but, the 40 pF one would give you the lower
frequency coverage you are looking for. I did not have any suitable
varactors handy but I am going to investigate that a little further.
Good sense tells me that the varactor approach would be better but, I
have not been able to prove it yet. This does however, show that the
capacitance of the 1N4004 diodes does vary quite a bit.
-------------------------------------
Charles R. Ott
K5HJ - QRP-L #1040
-------------------------------------
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