Topband: Need help in winning a Preamp Wager

[Tom Rauch]

> On the other hand, 11 dB seems high for that length of
that cable at
> 1.8 MHz. Have you measured that much loss?  If so, I would
be
> replacing it. Belden's data for 9258 ("sort of" equivalent
to RG8X)
> is 0.37 dB/100 ft at 2 MHz. That works out to just over 5
dB for 1400
> ft. At 80 meters, it's more like 0.55 dB/100 ft.
>
> Have you found receive antennas on 160 to be circuit noise
limited
> with the preamp in the shack?



My longest feedline is 1500-2000 feet of F-11 cable with
maybe 500 feet more of RG-6 after the switching hub. While
my antennas have two (or three) phased Beverages in
broadside with 300-400ft spacing with 3db or more
sensitivity than a single Beverage antenna. Of course
background NOISE is 3dB less also, so it is a washout with
the gain. It pushes noise floor down while signal level
increases. (Close spaced broadside Beverage antennas won't
push the noise down. Noise and signals come up equally. You
have to be out near 5/8th wl or wider spacing.)

All of my noise when the band has useful DX signals comes
from propagated skywave noise, so it's as quiet as it can be
in this area.

All of my preamps are in the shack. That's true even with my
close-spaced phased vertical arrays. They are still very
clearly skywave noise limited.

A very small antenna with -20dB gain in a very quiet
location (like mine, where all noise is skywave noise) and a
narrow receiver bandwidth in the IF filters might create an
issue. So might a single Beverage in a very good location on
a long line that isn't matched well.

By the way, the RECEIVER sets the SWR in a receiving
system....NOT the antenna. You have to calculate feedline
loss based on the RECEIVER mismatch, and some amplifiers,
multicouplers, and receivers have awful input impedance
mismatches. The antenna mismatch only represents energy
transfer losses into the feedline. Lossy systems are NOT
bilateral, so you can't use the same loss both ways when the
system has mismatches.

My system is almost perfectly matched looking INTO my
receivers, filters, and amplifiers. What I see might not
apply if you have a gross mismatch at the load end of the
transmission line, which in this case is the receiver....not
the antenna.

73 Tom