Thanks, Rick. I think you are fortunate to have a low noise level where
you could actually use your TX Antenna.
My situation is that if I tried to listen on my transmit antenna I would
only work the very strongest of signals. Typically the noise moves the
meter to about 20-25 over S9 if I listen on my vertical. The best success
I have had is with a Beverage, but whether on any given trip I can put one
up largely depends on whether any of the four or five people's property I
would cross are there and whether they would allow it or complain about
it. On my own property, the only thing I have done is put up a little
triangle with the top at about 20 feet and the bottom wire in the
neighborhood of 30-35 feet. That antenna has about -37 dB of gain. A 15
dB preamp plus the preamp in the transceiver makes it an OK antenna - good
enough that I have worked about 250 JA stations none of which would have
been worked if I were listening on my vertical. And I am guessing that if
I had a 3 dB improvement in S/N ratio that I would have worked 400 in the
same time period. That antenna has an RDF of 7.7. Always wanting
something better and if I could put up something I could rotate with an RDF
of 11 or so, I would hope to be content.
Stan
Stan
On Sat, Dec 15, 2018 at 1:47 PM Richard (Rick) Karlquist <
richard@karlquist.com> wrote:
> 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
> > _________________
> > Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
> >
> >
>
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