General response, not specific to the Waller Flag:
For a number of good reasons, you should not expect
a NF below 3 dB for any practical preamp. OTOH,
virtually all radios have an internal switchable preamp.
Let's say your radio is really pedestrian, and the
internal preamp has 10 dB NF. Neglecting feedline
loss, your preamp gain only needs to be about 13 dB in
order to the preamp noise to dominate over the radio
noise. Any additional gain above that will not help
you "start to hear band noise" but will instead hear
preamp noise. Some ops like to use additional gain in
the preamp to make the AGC threshold occur at a lower
level. This reduces listener fatigue, but does not
actually produce any newly-readable signals.
If the above isn't correct, can someone give a worked
example of where a 40 dB preamp would make sense?
FWIW, I tried a Waller loop last year in the 160 meter
contest. It was quite large (I have plenty of space).
It seemed to be working OK in terms of being directional,
but it almost never improved the readability of any
signals vs the vertical. IOW, aiming it at Japan didn't
help work JA's, except to the extent that it reduced
stateside QRM. On a clear frequency, there was no advantage.
73
Rick N6RK
On 12/15/2018 11:15 AM, Stan Stockton wrote:
I am curious to know if anyone on here has scaled a Waller Flag to a
smaller antenna and had any success with whatever might be available for
preamps to bring the gain up enough to start to hear band noise.
At my location on Cayman Brac I could probably get by with a 20 foot boom
but not much larger. According to my model, one with a 50 foot boom is
about -48 dB, one with a 30 foot boom is about -65 dB and one with a 20
foot boom, like I would lilke to put up, is about -79 dB.
I guess a lot to do with how successful the antenna might work for me will
have to do with how much preamplifier gain I will need at my particular
location to start to hear noise. I wanna use it on 160, 80 and 40 and the
gain of the 20 foot boom one is enough for 80 and 40 using a 30 or 40 dB
preamp.
Any help would be appreciated.
73 and Merry Christmas...Stan, K5GO/ZF9CW
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