[MRCA] Antennas

[ersmar at comcast.net]

Rich:

      If you look at the top view illustration on the URL below, you'll see that the wire lengths are different on each connection point of the SO-239.  That is, there is a 25 foot long wire and a 38 foot long wire on the center conductor and on the outer (ground) connector.  This would result in two CENTER-fed crossed dipoles (One pair of wires being 25 feet long and the other 38 feet long each side of the feed.)  

     I modeled both the center-fed and the off-center-fed (both 25 ft wires on outer conductor and both 38 foot wires on center pin as Al's antenna is configured) and found they are almost identical in electrical characteristics (resonance points, SWR and impedance variation across the freq range from 3.5 - 10.5 MHz).  I didn't look at radiation patterns, though; too confusing to compare various plots at various freqs between the two!  

BOTTOM LINE:  The URL you refer to below IS the actual construction of the AS-2259, plus or minus a few inches, except for Al's, which has the 25 foot wires on one conductor of the SO-239 and the 38 foot wires on the other.  


73 de
Gene Smar  AD3F

 -------------- Original message ----------------------
From: "Richard Arland, K7SZ" <richard.arland at verizon.net>
> Al, et. al:
> 
> I have been surfing the web and found quite a bit of info out there on NVIS 
> antennas. Here is a link that shows the layout of the actual NVIS antenna. 
> The deminsions are not exactly the same as what Al gave in his message 
> (attached) but it looks exactly like two off-center-fed dipole antennas 
> spaced 90 degrees apart.
> 
> Go to: http://www.vcars.org/tech/NVIS.html and have a look. Is the AS-2259 
> similar in construction?
> 
> 73 Rich W3OSS
> 
> 
> 
> > Hi Gene,
> >
> > Short elements are 24' 9" and the long ones 36' 11".
> >
> > I've always been confused by the disposition of these elements.  The two 
> > short ones are connected to the center conductor of the mast, and angled 
> > at 90 degrees to each other.  The long ones are connected to the outside 
> > of the mast, angled at 90 degrees to each other, 180 degrees around from 
> > the short elements.  So the antenna seems to be crossed Windoms rather 
> > than crossed dipoles.
> >
> > I'm not sure how important a matching network is with a true field radio. 
> > They'll about load a wet noodle.
> >
> > Regards,
> > Al
> 
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