Hi Guy,
Some of it is high ground penetration on low frequencies. Dipole
height above 'real conducting' ground can be a lot in some locations
73Bruce-K1FZ
-----------------------------------------From: "Guy Olinger K2AV"
To: "Richard McLachlan"
Cc: "topband"
Sent: Wednesday December 16 2020 11:22:24AM
Subject: Re: Topband: Rogers dipole
I don’t at all doubt Roger’s reports. The grind comes when others
attempting Roger's successful methods report terrible results. There
is
clearly something going on not at all well understood.
There are some number of reasons why it is nearly impossible to draw
universally reproducible conclusions from Roger's successes.
(1) The VOACAP program and its various published results are the root
genesis of a lot of individual hams’ propagation angle head-guess
gut-feel
SWAG.
VOACAP cannot evaluate high angles and low angles in the same program
run.
Fortran limitations. Common variables calculating space, etc.
That limited range wasn’t a problem for the original VOACAP
developers
because they were servicing an inquiry on most reliable angles for
persistent commercial style broadcasting. As in a distant listener
with
very limited radio and antenna hearing the station’s broadcast for
an
ENTIRE and
PRESCHEDULED hour without dropouts.
The low angles were the recurring, reliable angles, even if not
always
the strongest path and certainly not the easiest to build to and
transmit. The low angles got all the press because they serviced the
money
that was paying for the development. High angles are not reliable for
broadcasting hour long programming. Even if the low angle was weaker,
more
power/tower invested in the low angle transmission solves the need
for
reliable propagation angles.
Getting through strongly for a minute or so on top of fading cycles
to
allow hams to trade names and RST on CW was *NOT* in VOACAP developer
goals, though that certainly would satisfy and make joyful virtual
legions
of ham operators who only need to hear their call and 599 coming back
from
a new country.
7 MHz research at NY4A compared a yagi at 135' with a lower long 5
element
quad centered at 85', with unexpected results. Often the higher
antenna
would experience deep fades on European stations while simultaneously
the
lower quad maintained a steady S9 plus.
Trying to explain results with VOACAP, the higher angles on 7 MHz
were only
obtained and collated when VOACAP was A) run for lows and then B) for
highs, and the results manually combined into a single presentation
A)
*and* B). At that point you could see that for at least short periods
the
high angle was predicted very useful. Certain angles were not invoked
by
the high yagi, a deep null between major lower and upper lobes. But
all the
literature only considered the low angle runs of VOACAP.
The high angle VOACAP results predicted frequent if short interval
arrival
angles that were a vertical null in the model pattern for the yagi at
its
height. After that we never bothered to put that yagi on EU DX.
Always used
the quad. Regular VOACAP runs never exposed that in the same way they
don’t
expose Roger’s riddle.
(2) There is no commonly available inexpensive equipment for hams to
detect
what arrival angle is being heard. We INFER that it's coming high or
low by
what antenna is receiving, and that distinction depends on our mental
remembrance of challengeable model plots (not measurements) of gain
vs.
elevation.
(3) The veracity of (2) depends on whether the model's use of ground
conductivity and its effect on patterns is actually true in the wild
variation of ground conditions found across hamdom and local
consistency of
same. From ham to ham across the globe there is WILD variation in
ground
characteristics, almost never monolithic as necessarily presumed in
the
model programming.
Since these days we have drones that can carry measuring devices that
talk
back to a tablet over Bluetooth, some actual measurement of
almost-far-field vertical pattern is possible, but I have not seen
such
measurements carefully tabulated and compared to NEC predictions.
Everything I have seen is measured at the ground. Standing man with
meter.
SMWM.
(4) We are sky wave folks. Measurement of TX at the ground tells us
squat
about absolute sky wave intensity at the same azimuth. We can only
infer
that azimuth-wise variation in field strength at the ground similarly
modulates azimuth field strengths at elevations significantly above
the
horizon. Yet even that is suspect from NEC 3D pattern data on some
antennas.
(5) At distances far enough to truly, absolutely be far field with
any
local ground involvement completely accomplished, upper elevation
measurements would have to be at aircraft altitudes.
SMWM doesn't cut it. We need FLYING man with meter. FMWM needs
helicopter
services, or high altitude drones. I have personally done helicopter
measurements at altitude, documenting azimuth AND vertical pattern
from a
problem TX antenna for an FM broadcast station at 89 MHZ. I was NOT
paying
the chopper service for that out of MY pocket change. Very pricey.
Got money, TX stuff like that can be done.
For both myself and the pilot, getting to GPS testing coordinates and
altitudes, constant coordination with RDU air traffic control, and
constant
lookout for other traffic made that afternoon a wild, breathless,
nerve-jangling experience. Measurement documentation DID convince the
antenna manufacturer, and relief was forth-coming. But since it is
now
quite clear I don’t have the nerves to be an air traffic
controller, not
sure I ever want to do that again.
Somebody want to invent something less than mil-spec expensive that
will
measure signal arrival elevation angles? I'd sure pay money for one.
Get
some good drone elevation TX measurements. Then see such basic stuff
as
whether sent high angle creates received high angle, with any wave
tilting,
etc. Things that ham short QSO results simply cannot tell us.
I've seen quite a number of stories in this string of threads. I have
no
question they are all telling the truth about their experience. Their
experiences seem contradictory, but they can't actually be
contradictory
unless quite some number of those reporting are deluded or incredibly
mean
spirited. I don’t think they are. We simply don't have the tools we
need to
explain the divergences.
I can tell you one thing, don't bother with a low dipole on 160 in
the
North Carolina Piedmont. BTDT. Sucks. Doesn't hear well, doesn't
transmit
well. There's something going on with ground loss and with pattern.
SOMETHING going on.
If we could just ever get past that SOMETHING.
73, Guy K2AV
On Sat, Dec 12, 2020 at 3:07 PM Richard McLachlan
wrote:
> Roger’s dipole certainly seems to work. From time to time when
everybody
> here in the U.K. is busily CQIng with no response from NA, I listen
on an
> East Coast NA web SDR and compare signals from this end including
mine.
> This is not at sunrise or sunset at either end. Roger is almost
always up
> there with the big guns, all of whom are using verticals as far as
I know.
>
> Richard G3OQT
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