I can heartily confirm Bob's experience. I live in Iowa and moved from the
suburbs of Des Moines to a rural setting 22 years ago. I have a well
constructed overhead single phase 13.2 kV distribution feed on the road 1/4
mile from my home. My house is fed underground from the pole to the
transformer and underground from there to the house. When I first moved
here my mid-day noise floor on a 1/4 wave vertical antenna ran around -125
to -130 dbm (300 hz bandwidth). Switching from no antenna to the 1/4 wave
vertical on a sunny mid-day made a obvious but fairly insignificant
difference. I
had very little man made noise. I then added a four square transmit array.
I
subsequently put up several single wire Beverages, two-wire reversible
Beverages, and was the first to build W8JI's passive/tuned vertical array
design (which, oddly enough, had a simple design error which Tom quickly
caught and corrected). While all the RX antennas worked, they rarely out
"heard" the four square TX array and if they did, not by much. Remarkably,
they didn't "out hear" the 1/4 vertical by a whole lot many times either. I
began wondering if all these RX antennas were somehow defective (it's kind
of hard to screw up a Beverage). The answer proved out to be. . .they were
all working fine.
I have mentioned this a couple of times over the years but perhaps it's
worth noting.
The bottom line is. . .if you have a really quiet QTH (getting to a rarity),
having a
terrific RDF doesn't buy you much in terms of improving real S/N performance
(with no "N" ?) and true ability to hear. If you are fortunate enough to be
in this
situation, you also quickly realize quiet low gain RX antennas are often
noise figure
limited (on several occasions people kept telling me "you just need more
gain". .
not necessarily so).
About six or eight years ago I put up an early Hi-Z 8 circle array which has
and continues to
perform extremely well. Interestingly enough, many times it doesn't hear
all
that much better than the four square TX antenna (but putting it in
diversity
is a huge help). That said, with all the encroaching rural homesteads being
built
with a mile or two, my noise floor over the past five years or so has slowly
crept up to
about -115 or -120 dbm. Sometimes I'm seeing -115. Lee/K7JTR understands
the
low noise floor issue very well and, at my and others behest, developed the
+6 amps
for the Hi-Z antennas with improved NF. He and I have had discussions about
improving
this further but, frankly, I'm not certain there is much of a market for
people with true -130 noise floors. . .hi. With my ever increasing noise
floor, the
performance difference between the Hi-Z 8 and the TX antenna has become more
apparent.
Sadly, my quiet QTH is not as quiet as it once was making RDF now matter
more.
See you all in the Stew. 73 and Happy New Year to all. . .Dave, W0FLS
-----Original Message-----
From: W7RH
Sent: Friday, December 28, 2018 11:04 PM
To: topband@contesting.com
Subject: Re: Topband: Topband Digest, Vol 192, Issue 33
All,
Two cents worth of comments on thread. The SAL, K9AY and Waller Flags
all work well and have their limitations. They do help the city folk
improve the ability to receive. The WF works great if you can get it up
in the air and rotate it. That is if you can keep it there in one piece
though snow , ice and wind. It also encompasses additional costs for
tower support and rotator.
The larger passive and active arrays specifically 8 circle provided you
have space are better yet with great RDF, realistic gain and noise figures.
There is a cross over point where there is no longer any improvement
IMHO. I'll point out an example. In the morning hours before sun rise my
noise floor drops to near zero on my RX/TX array. I'm extremely
fortunate for I have the space and no neighbors, no commercial power and
thus only natural noise. A reasonable guess would be a noise floor
greater than -120 to -125dB. Almost to the point of MDS where there is
no indicated or measured difference between antenna and no antenna.
Working signals via polar path, NW, West and SE are _on average very
very weak._
My experience tells me that active loops would be inferior to the
existing directional RX/TX antenna at this point because of their signal
capture levels and increased noise created by preamplifier. In this case
only long properly terminated and maybe phased beverages would be better.
I can feel the heat coming on this one. I'm not here to sell antennas as
I build my own.
73 and Happy New Year!
Bob, W7RH
--
W7RH DM35OS
It has become appallingly obvious that our technology has exceeded our
humanity.
Albert Einstein
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