Topband: Preamp update

[i4jmy@iol.it]

W7IUV:
> If anyone builds the pre-amp, I'd like to hear how it worked for you.

A loop with a resistive termination is inherently broadband. It has a 
very low efficiency on lower bands but its attenuation decreases in the 
higher part of RF spectrum. Delivering a lot of unwanted signals to the 
active device worsens the IMD figure (a two tone test it's different 
than a test with more tones). I find smarter a preamplifier that 
includes an input band pass filter (not a Bessel) so allowing the use 
of an active device with a lower NF and eventually an higher gain.
Different band pass filters could be switched remotely by different 
voltages, or by a tone (or different tones) through coax, like it 
happens with LNBs in satellite home stations.
Another point, useful in case of long coax runs, could be to place the 
preamp directly at the antenna side. In this case the filter could be a 
900 Ohm input and 50 Ohm output so eliminating the need of a step down 
transformer.

73,
Mauri I4JMY


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