[MRCA] 3.885 NVIS antennas

[jeepp at adelphia.net]

 NVIS works at the lower end of the HF spectrum, up to about 8-10MHz.  Above 10MHz, again as I recall, NVIS is not really an option.  I'll re-read my text from an HF course (GWU).  D-layer absorption causes severe fade out on the lower end of the HF spectrum by late morning.   This has been demonstrated time and time again by us in CAP.  Inevitably, our 4.5 MHz frequencies fade by about 11am with virtually no propogation, thereafter.  
de K3HVG
 
---- Gene Smar <ersmar at comcast.net> wrote: 
> Al, Rob et al:
> 
>      I've been doing some reading and thinking about our earlier e-mails
> regarding HF NVIS work at the MRCA in September.  Before we get too set on
> this demo, won't 3.885 be too low a freq for daytime work?  And if we want
> to go to 7 MHz, what military gear would cover that band?  (Maybe a GRC-9 or
> PRC-47, but the BC-1306's cut off around 6.5, don't they?)  And 60M requires
> ultrastable rigs with freq resolution down to the cycle.
> 
>      We (or at least you guys with the HF rigs) could TRY 3.885 during the
> days' demos, but I'm not certain that'll work.  Anyone have any other
> thoughts?
> 
>      I've been reading about NVIS so I could try to brew up an AS-2259
> equivalent system to lend to someone with HF gear at MRCG.  I bought a set
> of fiberglass poles on ebay
> (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=5780368768 ) to serve as
> a mast.  I was thinking of running the coax up inside the sections and
> connecting to the wire sets through a 1:4 torroidal balun.  Seems that low
> dipoles/V's exhibit low feedpoint impedances, thus the need to convert from
> 50 Ohms to 12.5 or so Ohms.  (I'll do some EZNEC Lite models before I start
> building.)  Click on http://www.co.missoula.mt.us/acs/radios/AS-2259%20M.htm
> for additional mods some folks have devised for the stock 2259 antenna
> system.
> 
>      In any case I'll be bringing along some VHF squad radios for demos on
> 51 MHz.
> 
> 73 de
> Gene Smar  AD3F
> 
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