Topband: W7IUV Preamp from Low Band DXing

[Ford Peterson]

Tom wrote:

...snip...

Be very careful what you do with gain distribution or adding adjustable gain
to preamps! The last thing you want is to reduce gain while making strong
signal handling worse.

My bet is you can do it all with input attenuators, some filters, and one
strong IP3 preamp for the really low level antennas. My preamps are all in
the mid-40's or higher output IP3. I then pad and filter the inputs as
required. I find I only need remove the AM BCB by about 10-20dB to eliminate
problems. Without doing that I can dimly light a 12v dial light on the
preamp outputs just from AM BCB stations!

73, Tom 

******************************

Thanks for the thoughful response.  I keep thinking in terms of boosting
gain.  It's an emotional problem of sorts.  I'm predisposed to NOT put
resistors on my antennas.  Hi.  I'll check the yellow pages to find some
professional help for that...

All my Rx antennas hear noise, so I conclude that they do not establish the
noise floor.  And the longest run of coax is low loss and <500'.  So maybe
what I should build is a multiple attentuator and incorporate a relay
switching arrangement to balance all the Rx antennas to the same level on a
quiet night.  Hmmm...  The wheels are turning.

With respect to the attenuator topology, a simple resistive PI circuit could
be used to maintain Z while inserting some loss.  Is this the approach to
use?  Or can a fella use bias on some Pin Diodes to throttle the signal
output?  I like the notion of setting the bias on Pin diode approach the
best (no resistors in the signal path hi hi).  But this may likely introduce
significant IMD if I don't do it right.  In fact, using the pin diode
approach I can incorporate a switching scheme in the same circuit (e.g.
choke-off unused antennas and properly bias the desired antenna).

I'd like to get it right the first time.  Your thoughts on Attenuator
topology?

Thanks and 73

Ford-N0FP
ford at cmgate.com