I stand by my remarks.
On Wed, Oct 24, 2012 at 6:25 PM, Richard Fry <rfry@adams.net> wrote:
> Guy Olinger wrote:
>
>> I have not personally seen work to validate signal strength and prove the
>> mechanics of arrival at various altitudes at 50 km. ... NEC4 says that
>> it doesn't continue. But NEC4 also nicely predicts the 2.8 km helicopter
>> measurements.
>>
>
> This depends totally on the accuracy of the NEC model, and the analysis
> that the NEC operator asks NEC to perform -- which depends on the
> background, skill and experience of said operator.
>
> A NEC far-field plot shows zero relative field (E/Emax) in the horizontal
> plane, and not much more at low elevation angles above it.
>
> A plot close to the radiator that includes the surface wave shows that
> radiation from a monopole is maximum in the horizontal plane, and not much
> less than that for low elevation angles above it -- which low-angle fields,
> in reality, are space waves. There is nothing in physics that would
> preclude those low-angle fields from propagation on to the ionosphere.
This still does not substitute for the lack of confirming data at farther
distances.
If there is data contradicting NEC4 out at distances like 50 km, bring it
on. We would all LOVE to see it. That would be a helicopter descent from
operational altitude limit to ground at 50 km. At that distance NEC4 has
inserted the severe notch it correctly does not predict at 2.8 km. If
sitting-man-with-meter-in-helicopter comes back with a curve that
contradicts NEC4, we finally would have a MEASURED reason to have them fix
it. NEC 4 near field calculations *AGREES* with you at 2.8 km, but its
calculation of physics simply extending the distance variable in the same
calculations out to 50 km does not.
So far NEC4 has predicted any real measurements, regardless of operator
skill. And isn't it just a little bit too easy to dismiss any contrary
opinions as operator error? :>) Doesn't bother me at all, one way or
another, but you have insinuated some really fine people I know.
> There apparently is completely zilch commercial interest or need for the
> answers to our speculations.
>
> Not so, sorry. Class A (50 kW, non-directional, 24/7) AM broadcast
> stations depend on this low-angle radiation to produce their large coverage
> area footprints, at night. This low-angle radiation is equally important
> to hams, but apparently is not recognized by most of them.
Of course they "depend on it." But they are not depending on your
explanation. They are depending on WHATEVER delivers the goods. The same
way they depend on gravity and a supply of power. So what.
"Depend on it" and "commercial interest/need for expending money to obtain
the answers to our speculations" are two completely different ideas.
They've already paid to harness WHATEVER governs their coverage and have no
monetary interest in the latter. They already have their station's coverage
performance in hand. Why is a station manager going to spend money hiring
a helicopter guy to answer some ham ops' curiosity about modeling low
angles at distance and explaining the physics of it? They have the
day/night coverage they're licensed for. They don't care unless they don't
have it, or there's a way to reduce their power bill and still keep it.
They want to cover their area and not have problems with other stations
and the FCC. On the whole they don't care about working DX. It only gets
them in trouble if they're not clear channel. So there has never been
anything in there to drive research into the pockets and closets that would
answer these questions of ours.
For the vast majority of stations, night-time propagation is a barely
controlled PROBLEM that can only get them in trouble with co-channel
stations, where dealing with that either shuts them down at dusk, or forces
them to go directional and/or reduce power, and sometimes detune newly
built local vertical structures to keep their nulls. Mostly, if you think
about it, they are designing their stations to NOT work DX at night.
You know a station manager interested in paying for the helicopter when
everything is peachy? Roll 'em out. We have a proposition for them.
In my college days at Berea, Ky, I would listen at night to clear channel
> 650 WSM in Nashville (Grand Ole Opry, etc), using a 195 degree tower,
> supposedly the Cadillac for low angle transmission. In the daytime at a
> distance of 165 miles, the 50 kW signal was there but very raspy to the
> point of irritation at Berea. I learned not to bother turning on that
> station during day.
>
> No surprise, there, especially if you were using a Zenith all-American
> five in a dorm room. Probably a good car radio even a bit beyond Berea, KY
> would/does receive a noticeably better daytime signal from WSM than you
> report.
>
> The WSM daytime signal in Berea at 165 miles would be groundwave, which
> for those conditions will be relatively weak. The WSM nighttime signal
> in/near Berea would be mainly skywave, which might average more than 10X
> greater fields than their day/night groundwave there.
>
Nothing like living in the south central area of Kentucky for eight years
of your life to KNOW what's around there. Oh, sorry, misspoke, the Zenith I
had in Columbus was a 5 tube. The Zenith in college was a larger bakelite
desktop case with push-pull audio, and a heavy speaker that sounded really
good in that case.
Of course the dormitory at Berea was some sort of attenuator. But the
attenuation was the same both day and at night. So the DIFFERENCE between
WSM day and night would remain the same, inside or outside the dorm. The
difference was WAY more than 10x. We're not talking about FM capture
effect. But we are talking about an AM station going from unbearable
scratchies daytime to SOUNDING like FM full quieting at night. I was
there. Whatever propagation was in effect was gangbusters at night.
Also, if one MUST have a graph, try
http://radio-locator.com/cgi-bin/pat?call=WSM&service=AM&status=L&hours=U
Berea would be a tiny bit south of Lexington on this map. Berea is
definitely in WSM's far fringe. The map definitely matches my experience.
The old town, college part of Berea is up on a ridge that is the boundary
between the Appalachians and the Bluegrass.
Up high on the western edge of the ridge, we had a breath-taking view of
SW-NW-NNE from the roof of Pearson Hall out over the Bluegrass. We had the
best spot imaginable for reception from WSM. The ham station's 80/40 meter
OCF wire we had suspended from a drain vent on the roof over to Howard Hall
played like gangbusters with 35 watts CW. Location, location, location.
In the general direction of WSM, there's nothing that could obscure even
the low 1/4 degree line of sight. Google Earth 37.574 -84.2916. That's
Pearson hall.
WSM was noisy weak in the daytime on top of the ridge, just like the graph,
and no noise at all sweet listening at night, every night, all night. It
was better sounding than records when they were broadcasting live, which
they did a lot. You couldn't tell it was coming from a box when they were
live.
Daytime WSM disappeared anywhere east off the ridge, down in the valleys.
Night time copied them full clear through the mountain valleys of eastern
Ky, Tenn, and western NC all the way to Morganton, NC. Talking about
driving in notch valleys with parallel ridge peaks 1000 feet or more
overhead up at a 45 degree angle. There are lots of reasonable questions
about how that worked, like how could that work with a low incoming angle,
and no hard research to push EITHER WAY. The first thing would be to prove
that NEC4's null at 50 km is a fantasy. If it is, then there are problems
in the equations being used to calculate, and that presses up against a
widely held conviction that NEC4 delivers the goods for BC band. If that
were the case, who knows what we find crawling under that rock.
Where's the helicopter at 50 km?
73, Guy.
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Topband reflector - topband@contesting.com
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