TT:
My final offering on the subject. Another reason that NVIS is used by
milcom folks for real is that it's hard to DF an NVIS source (or so I've
read.) Because the signals come down from almost directly overhead the DF
receiver must be within ground wave range of the transmitter, i.e., within a
few miles.
Stay safe.
73 de
Gene Smar AD3F
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
jimlux
Sent: Tuesday, June 09, 2020 12:39 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] NVIS (not exactly towers, but HF)
On 6/9/20 8:59 AM, Gene Smar via TowerTalk wrote:
> TT:
>
> Regarding ridiculously low dipoles and NVIS operation, they really
do work after a fashion. In addition to towers, I collect military radios
and am a member of the Military Radio Collectors' Association
http://www.mrca.ar88.net/ . We meet on the air several times a week on HF.
We also attend an annual gathering of the membership (predominantly east
coast) each September in Gilbert, PA, in the Pocono Mountains. Here we
actually use our shorter-range 51 MHz FM radios as well as our backpack HF
rigs that the US Special Forces used in 'nam. Several of our members have
told hair-raising stories about their use of these packs in the field.
>
There's an awful lot of hams running 75m and 40m on "low antennas" - Sure,
most goes up, and that lets you do local comms, but it's not like there's NO
low angle radiation.
And a lot of people are constrained to low heights or verticals for one
reason or another - zoning, familial harmony, mobile/portable ops. After all
field day is in a few weeks - you're probably not going to erect a temporary
80 m 3 element Yagi so that you can rule the band.
Ultimately, it comes down to building more advanced planning tools like
HFTA. Right now people use HFTA to compare patterns to statistical
propagation forecasts (from VOACAP and it's ilk).
I think, though, that there might be some fruitful work on a more tactical
basis - people with crank up/down towers might find that there are "better
heights" based on propagation *measurements* and modeling.
(whether the model is in the brain of an experienced DXer or on a computer,
it's all the same)
For those seeking professional literature on longer distance paths, look at
over the horizon radar papers - OTH radar is not NVIS, almost by definition.
And while you may not be able to set up 50 big LPDA antennas in a row with
miles of coax and 50 amplifiers, a lot of the analytical techniques they use
are useful to hams. Chris Coleman, VK5AHZ and G4HCW, in Australia, has done
a lot of work for HF OTH radar, but also produced useful stuff for hams in
terms of things like modeling the spatial distribution of lightning noise,
and frequency management for low frequency radio telescopes, like I work
with.
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