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Noise, Bandwidth and Gain



  It is one thing to learn something by the book, and another altogether to
see it in action.
  I have been playing with a Drake 2880 downconverter and the Conifer PreAmp
and antenna combination.  My Drake is unmodified as yet.
  I live in Frankfurt, Germany and as anyone who has lived or visited here
will know, along with the typical RF noise of a large metropolitan area,
there is a large tower that radiates many kilowatts at frequencies from DC
to daylight.  If that tower were to fall over in my direction, I am a dead
man.
Any attempt to monitor AO-40 or any other signal at S-Band has been
fruitless.  However, I recently added a cavity filter cut for 2.4 MHz
between the Conifer amp and the antenna and WOW!  Signals have appeared from
nowhere.
  I'm still not there yet and I have decoded no signals, but the following
notes include lessons I've seen in action today:
First, Average and PEP power applies to my S-Band, small signal environment
just as it does for a 1.5KW HF station.  While there may be no one signal
that will saturate my system, the sum total of signals that is accepted by
my receiver front end may add up to a PEP that does drive the front end into
nothing but noise.
Second, the term "Preamplifier" is a misnomer.  While one might think that a
PreAmp is an outboard stage of added amplification, from my perspective
PreAmplification is the sum total of all active stages and associated gain
prior to signal detection.  The amount of gain or the link budget in any one
situation or at any one time with a fixed station changes dramatically.
Were it not for receiver dynamic range, this whole process of Ham Radio
would be nearly impossible.
Third, an attenuator is just as valuable as an active amplifier.  Both have
their place and both can be used together to achieve the ultimate goal of
signal reception and the act of decoding information.
  If you've read this far, you either feel my joy of learning or you are
board stiff.  For me, sitting in front of my test bench today was fun!!  I
don't know if talking to others on AO-40 is more of a kick or if learning
the technology is what I'm after.  Probably both.

73

Gary, N7BRJ/DA1BRJ


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