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RE: S band for 6 bucks

Someone wrote:

"Could one leave the output of the downconverter at 20 MHz if one had an
IF rig that could receive at that frequency? Or is there perhaps an 
filter that expects VHF output. Under these conditions, one would only
need to retune the input filter, avoiding  what seems to be the most
hazardous part of the refit".

The Cal Amp 130215 S-band downconverter converts a 2.5 GHz. input freq.
to an IF output of 120 MHz.

If you try to use the downconverter to tune 2.4 GHz. without modifying
the Local Oscillator (LO) frequency, you would have an IF of 20 MHz.
While this may sound appealing to some, it is not practical with this
downconverter without other modifications.

I did not take detailed measurements at other IF frequencies, but I
noticed a sharp drop in downconverter sensitivity once the IF output
dropped below 50 MHz.

The following chart shows a 20 dBm improvement at 2.4 GHz. in the
downconverter once I converted the IF output from 20 MHz. to 144 MHz.

Downconverter input level = -70 dBm
(A) = Unmodified Cal Amp 130215 S-band downconverter
(B) = Cal Amp 130215 - Retuned Combline filter only
(C) = Retuned Combline filter & IF changed to 144 MHz.

                              (A)              (B)           (C)
Input (GHz.)
2.40                         x           -58 dBm     -38 dBm
2.42                         x           -60 dBm     -38 dBm
2.44                         x           -45 dBm     -40 dBm
2.45                   -58 dBm     -45 dBm     -40 dBm
2.46                   -54 dBm     -45 dBm           x
2.48                   -42 dBm     -42 dBm           x
2.50                   -38 dBm     -40 dBm           x
2.57                  -40 dBm             x                x


AMSAT # 5562 
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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