> Being in possession of two ICE 160m bandpass preamps, I tried connecting
> them in series, but only got an S-7 noise, even with no antenna or antenna
> coax attached. Battery powering the preamps reduces the noise a couple of
> S-units.
You are trying for an absolutely unobtainable system noise figure if the
receiver has any sensitivity to speak of. For example, a 250Hz selectivity
receiver at -150dBm sensitivity would require a 0dB noise figure preamp for
3dB S+N/N ratio.
An ARR GAsFET preamp has about 3-4dB NF, and even the best design custom
amps would be around 1 dB or so.
Another way to look at it is like this. We can normally hear the RF
amplifier noise hiss of our receivers with narrow selectivity and preamp on
and the input of the receiver terminated in a perfect load resistor. The
front ends of our receivers are really pretty good. Now add 40dB of gain to
that, and imagine the "no antenna" noise!
No way could you ever build a preamp of any type that would allow you to add
40dB of gain to a receiver without a substantial increase in "no antenna"
noise floor. It is impossible because the active devices in the amplifier
are not even close to being capable of doing that.
About the best a receiver system could do is around -145 dBm with narrow
filters and a very good preamp, and I'm sure the ICE preamp isn't nearly
quiet enough to do that well.
You'd better rethink the antenna design! Low sensitivity antennas are OK for
very wide bandwidth modes like AM, but not for narrow modes.
73 Tom
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