[NLRS] Downconverters

[jcplatt1@mmm.com]

<SNIP>
Anytime you insert something into the signal path you incur
losses, the case for the downconverter seems to be:
which loss is greater, the loss signal at 23cm due to
cable length or the loss of signal due to addition of
downconverter.  Is this sound thinking?
<SNIP>

If I understand your question John, no, this may not be sound thinking.
Whether you use a downconverter with an IF rig or a stand alone 23 cm
receiver the exact same receiver processes are being used to get that audio
to your ear ..... gain stages, mixing, and filtering.    A downconverter
will have a conversion gain that is a useful specification that equates the
level of the input signal to the level of the output signal (from the
converter).   Very often the conversion gain is purposely designed to be in
the neighborhood of 0 to 15 dB or so.   The primary reason that someone may
use a downconverter at the antenna end of the feedline is to avoid feedline
loss that would otherwise directly add to your receivers noise figure.
The downside to doing this is the added complexity and exposure to MN
weather.

If your interest is receive only, it may be much easier to use a stand
alone 23 cm receiver in the shack with a remote mounted preamp which could
be place at the antenna.   Assuming your feedline run is not real long, you
could then use something like LMR400 as the remote preamp would really be
the driver in determining your systems noise figure.    Another thought is
to simply use the stand alone 23cm receiver in the shack and use a good
quality feedline like 7/8" Andrew which can be found used locally for a
fair price .... with the good quality feedline, no preamp may be needed.

The "VHF DX Book" written by G3?? (sorry, can't remember the author) is a
very very good book and has a chapter that talks about receive system
performance with respect to feedline loss, preamp gain, and noise figure.
His writing style is not overly technical and is really aimed at us
ham-types.  It really helped me understand trade-offs between feedline
loss, gain, and noise figure.    I highly recommend the book.

73, Jon
W0ZQ