Topband: Waller Flag Question

[Arthur Delibert]

Tom --

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):  

"During times of no detectable power line noise, we often noticed a curious effect:  The loop still enhanced signal-to-noise ratio by one or two S units, making copy of moderately weak signals more pleasant. . . . We believe that the unidentified noise is local and propagates by the ground wave.  We speculate that it may be the sum of hundreds of weak man-made noise sources in the densely populated suburb" (36).

This problem has only gotten worse in the years since.  Many 60-meter stations that I used to listen to are now on the lower 
edge of audibility, even on the best days.  (Yes, I know my ears are 
older than they used to be!)  At an earlier QTH, I built the antenna described by Beezley and it made a huge difference; stations that were barely hets with other antennas suddenly had fair audio.

At my current QTH, the layout isn't quite right for that antenna, so I've been looking for something else that will cut through the "fog."  My east-facing pennant does a pretty good job, but even it brings a lot of noise to the antenna port of the receiver.  And, of course, it's a fixed-direction antenna.

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?  

Art  


> From: w8ji at w8ji.com
> To: topband at contesting.com
> Date: Sun, 6 Sep 2015 14:53:55 -0400
> Subject: Re: Topband: Waller Flag Question
> 
> > 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.
> >
> > Is there now such a 40 dB preamp?  Is it made commercially? 
> > Alternatively, are there plans on-line somewhere?  Has someone actually 
> > used it in a high-RF urban/suburban area, with multiple 50 kW AM BC 
> > stations?  With what results?
> >
> 
> At some point we have to be realistic.
> 
> A typical receiver is somewhere in the -130 dBm sensitivity range, depending 
> on bandwidth and other things.
> 
> At -140 dBm and 250 Hz noise bandwidth, the system would require a 1 dB 
> noise figure front end.  That's about 35 deg K noise temperature.
> 
> If you need a 40 dB amplifier (or even close to 20dB) into a normal good 
> receiver, you will never get the noise temperature of things in front cool 
> enough to let external noise set noise floor. The issue isn't connecting two 
> amplifiers in cascade, the issue is the limit of noise temperature.
> 
> The only place negative gain antennas that require more than ~ 20 dB gain 
> with a normal receiver at a quiet location will work into the external 
> ambient noise floor generated outside the antenna is in a location blanketed 
> with strong local noise.  Besides that, if the gain is so far negative the 
> coaxial cable will easily become more of an antenna than the thing we call 
> an antenna.
> 
> 40 dB gain in front of a receiver is pure fantasy, unless the receiver is 
> dead as a door nail.
> 
> 73 Tom 
> 
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