Thanks for the insights. I have no doubt the theory is correct. My sense,
though, is that in the denser suburbs, we live in a "fog" of local radio
noise, generated by the scores of digital and other devices that surround
us. A similar observation was made 20 years ago by Brian Beezley, K6STI, in
a QST article titled "A Receiving Antenna that Rejects Local Noise"
(September, 1995, page 33): I've been looking around for something that
might work better than my present antenna, and I see good reports about the
Waller flag from people who are actually using it. So I'll give it a try
and see how well the theory matches up with actual practice. That's what
ham radio is all about -- no? >>>>
You said earlier:
The on-line materials about Waller Flags says that a modest size WF would
need about 40 dB of gain to boost the signal to a usable level. One of
the postings says that cascading two preamps of 20 dB each seems to add
extra noise, and they talk about developmental work being done on a single
preamp of 40 dB.
I'm not sure where "need about 40 dB of gain to boost the signal to a usable
level" comes from.
40dB is an unworkable amount of gain, unless the basic receiver is deaf.
Here is an example:
An Elecraft K3 has about -138 dB noise floor with preamp on. 40 dB more
gain, or -178 dBm noise floor, would require a preamp noise figure of -18dB
at 250 Hz BW and -24 dB NF at 1 kHz BW by my calculations. That's 100 times
less noise than no noise. :)
Maybe the reason people can't get two preamps cascaded to work isn't because
it is two separate amplifiers, but they are trying to do something
unnecessary and impossible? It seems to me 20-25dB would be more than enough
for most receivers.
73 Tom
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