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

[jimlux]

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.