[TowerTalk] NVIS (not exactly towers, but HF)

[Gene Smar]

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.

     To make a potentially long story mercifully shorter, we set up my NVIS crossed inverted Vee antenna (75M and 60M wires) in a mountain valley 20 miles north of our base camp at Gilbert.  We operated a 50 W HF rig on 75 M USB and base heard us Lima Charlie.  (Loud and clear.)  We then disassembled the Vees and held the 75 M wires taut at chest height and base was still able to copy us; a station in upstate New York also copied us LC.  The SpecOps guys among us told us that's how they used to deploy their skyhooks when they had no time to string the wires between trees.


73 de
Gene Smar  AD3F

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of jimlux
Sent: Tuesday, June 09, 2020 11:05 AM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] NVIS (not exactly towers, but HF)

On 6/9/20 7:39 AM, Rob Atkinson wrote:
> I didn't see anything in the abstract that made me want to read it as
> far as ham radio is concerned.   A number of hams over the past years
> have cited military work with cloud burners as a justification for
> their usefulness in ham radio.   I don't contest a horizontal antenna
> that has its highest field intensity straight up, but I do contest the 
> argument for ridiculously low hanging antennas because that's what
> other services do.   There are several differences between ham and
> other services that have to do with power limits, frequency 
> exclusivity, transmission modes, battle conditions, and radiation 
> efficiency.



what's interesting in the article isn't so much the NVIS stuff, but the modeling approach. They're doing some ionospheric ray tracing using ionosonde measurements.  For what it's worth, the antennas they are using are at 0.2 wavelength, which isn't one of those knee high wires. 
At frequencies from 4-11 MHz it seems.

They're using Coleman's ray tracing approach 21] C. J. Coleman, “Point-to-point ionospheric ray tracing by a direct variational method,” Radio Sci., vol. 46, no. 5, pp. 1–7, 2011.
Here's a report on it
https://apps.dtic.mil/dtic/tr/fulltext/u2/a271058.pdf

These days, there's a lot more real-time ionosonde data available - it's sort of the next step beyond NCDXF beacons or various reverse beacon networks.


Of particular interest is a paper I want to track down

[17] P. J. Coetzee, “A technique to determine the electromagnetic properties of soil using moisture content,” South Afr. J. Sci., vol. 
110, no. 5/6, pp. 1–4, 2014.

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