From: Dr. H. Paul Shuch (n6tx_at_setileague.org)
Date: Sun Aug 22 2004 - 17:24:00 PDT
Jesse Young wrote:
> I'm just curious to know what voltages most people are using with the
> Down East Microwave SETI-LNA and what effect (if any) this has on
> performance. The specs say 8-16VDC,
Because the preamp has a built in voltage regulator, it is very
insensitive to variations in applied potential, and there will be no
measurable difference in performance over a wide range of DC values.
>im feeding +12V along the centre
> conductor, but when I disconnect the bias-tee, there seems only a minute
> drop in the signal level.
Do you mean a minute drop in *signal* level, or in *noise* level? If
you have an actual signal source to test with, the difference should be
>20 dB. If it's a matter of listening to the noise level of your
receiver, depending on the mode, the change may indeed be quite small.
If, for example, your receiver is set for FM, there is a hard limiter
in the IF, and the unsquelched noise level will be relatively flat,
despite RF gain. If you're in SSB mode, you should hear a slight change
in background noise when your antenna is pointed at cold sky, because
the internal noise of the preamp is only about 2 dB. And in AM mode,
where AGC dominates, there may be no discernible change in background
noise at all. Best to check on an acutal offf-the-air signal, or create
one using the DEMI 1420 weak signal source or equivalent.
-- H. Paul Shuch, Ph.D. Executive Director, The SETI League, Inc. 433 Liberty Street, PO Box 555, Little Ferry NJ 07643 USA voice (201) 641-1770; fax (201) 641-1771; URL http://www.setileague.org email work: n6tx_at_setileague.org; home: drseti_at_cal.berkeley.edu "We Know We're Not Alone!"
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