[Premium-Rx] Broad Bandwidth HF RX Antenna + NVIS Antenna

[Ahmet Gundes]

RE: NVIS Antennas

I would like to add one more thing to the NVIS subject 
and its use as high-incident antenna:

Most NVIS antennas used by the military ( you can find some
explanation on this issue on the web site of Shakespear 
company that makes NVIS antennas ) are for VHF and UHF. 

This is basically due to the size/construction contstraints.
These antennas are used on military vehicles and size is
limited naturally. In order to have NVIS / High Incident 
angle, the antenna is made quite cleaverly as a Center
Fed Vertical Dipole ( most companies keep this as a little
trade secret ).  These antennas have "near vertical" dipole
performance. They can be used usually as low as 30MHz as they
are made to cover the military VHF bands.  However if the
vertical you have is not a Center-Fed Vertical and it is
a military monopole type then they are not NVIS type antennas
in its true sense.  The "old" Telex 4331 is a Center-Fed
Vertical and I believe you can get these from surplus dealers.
I have not seen any NVIS HF antennas that can go down to 
say 15MHZ range or so. They would have to be made for special
orders and they are not commercially available.  

One other way to experiement with the Angle Of Incidence is to
Tilt the Monopole ( usually about 10 - 20 Degrees ) as you will
see some hardware on military vehicles to do this. It helps a bit.

Regards
A. Gundes




> Well it looks like this thread has finally died down, I would like to thank you all for your input on my request for broad bandwidth HF antennas ideas. In a previous job I visited quite a few National Guard facilities and they were all using the B&W T2FD for HF communications. This is what originally got me interested in this antenna for band cruising. I really don't need an antenna that eaks out the last bit of performance for HF receiving purposes due to the high noise floor on the HF bands. I also saw a web site that did extensive modeling of the T2FD and if anything this scared me away from the idea of using it once I saw the analysis, however we all know that what a computer predicts and real world results are often quite different, this is why your input was so important to me. I also like the antenna idea that Al mentioned and to take it one step further I and probably most of you have seen the broadband dipole idea where a separate dipole is cut for each frequency b
 and and they are all attached to a common feed point. My question is has anybody tried this out and how did you like, also has anybody modeled it and what did the feed point impedance look like over frequency? Finally thanks for bringing up the NVIS antenna, it reminded me that I have one packed away somewhere, I think I'll set it up and see how well it works, even if it is a high angle antenna it might work out well for skywave.
>  
> Mark 

>
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