> >What defines "too much gain" can vary wildly.
Each install would be different. But too much gain
can be tested for... (measured) and with the proper
construction be fairly easily controlled.
> 0.1 uV is about as good as you can do with a NBFM RX,
> as that's roughly 6 dB above kTB when T=295 K (average
> earth temperature).
However, few locations manage an average (same year
round) temperature and rare seems to be the location were
the terrestrial noise doesn't throw a lead pipe into
the system performance. There is no noise free
location, but the level does vary more than people
would imagine.
> So I don't see any point in a preamp having more than
> 14 dB of gain, unless you're adding post-preamp lossy
> filtering or power splitters.
There are Northern California site locations in operation
where the Repeater Rx Antenna System contains the desired
pre-selection, two series pre-amplifiers separated initially
by an adjustable attenuator and later a fixed value. It's
beyond the scope of this post (IE right now) to explain
how the series preamplifier operation is dialed in with the
attenuator. But the end results compared to a single preamp
operation are dramatic and obvious.
I would have never considered a dual series RF Preamplifier
layout viable until I'd seen one demonstrated against the
single preamplifier version. The properly installed and
setup dual preamplifier layout with system gain well in excess
of 14dB clearly out preforms the rest of the bunch on the
same mountain top. I didn't invent it... but I've copied
the layout many times and it works killer (very well).
s.
