Yes, I know what he was looking for. He was thinking his 95 ft 80 meter
inverted vee was a low angle radiator, and that he may be able to
convert it easily into a high angle radiator when desired. Fact is, a 95
ft inverted vee is not a low angle radiator.
For ham purposes, an NVIS antenna on 80 meters is a dipole or horizontal
loop at about 50 feet. This give maximum radiation straight up.
For military purposes, an NVIS antenna was something different. In the
old days, NVIS antennas were used by the military to reduce the low
angle radiation so as to reduce the probability of being heard by the
enemy at great distances. The lower you go with an antenna the more you
attenuate the low angle radiation relative to the straight up radiation.
That continues until the antenna is lying on the ground. Of course the
signal radiated straight up is attenuated a lot also, but that is not
very important for this application. The best height would be that which
could just barely be heard by the intended station. Heights of 5 to 10
feet are typical. This is not a very useful antenna for ham purposes
because the gain is very low. And besides, most hams don't mind if they
are heard at great distances.
Antennas arrays that provide large amounts of gain directed straight up
with very narrow lobes aren't very useful for ham purposes either.
Building one of these would be a lot of trouble, and the only thing you
would gain is for stations maybe 50 to 100 miles away. You could be 60
over S9 instead of only 50 over S9.
Jerry, K4SAV
ersmar@comcast.net wrote:
>Jerry et al:
>
> Such antennas (low to ground, high angle radiators on bands up to around
> 10 MHz) are more commonly know as NVIS antennas (Near Vertical Incidence
> Skywave.) There are quite a few references to such on the web. (See
> http://www.co.missoula.mt.us/acs/antennas/NVIS%20EZNEC.htm and
> http://www.w0ipl.net/ECom/NVIS/nvis.htm - scroll down to N7NVP and W6QJI in
> What Works Well?)
>
> Their use in Ham Radio circles (and military, for that matter), is for
> improved <skip-zone> coverage, i.e., that area around a transmitter where
> ground wave fades out and before the first E- or F-layer bounce on the ground
> occurs. Most literature that I've read on the subject considers this
> distance from 50 to 500 or so miles out.
>
> Hams would use such antennas for domestic contesting, i.e., SS or Field
> Day, or for EmComm activities where local infrastructure has been damaged and
> receive points are beyond V/UHF range from the disaster sites.
>
>
>73 de
>Gene Smar AD3F
>
>
>
>
>
>>It is possible to build arrays that squirt the signal straight up with
>>significant gain, but the beamwidth is fairly narrow, and these antennas
>>don't seem to have any applications in ham radio.
>>
>>Jerry, K4SAV
>>
>>Joe Barnes wrote:
>>
>>
>>
>>>I am considering putting up a wire about 1/4 wave below my 75 meter
>>>inverted vee that is 10 percent longer than the inverted vee to use it
>>>as a reflector for closer in ( within 700 miles or so) communications.
>>>Does anyone have any experience with such a thing? The inverted vee is
>>>at 95 feet at its apex. Thank you, joe barnes N4JBK
>>>_______________________________________________
>>>
>>>
>>>
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>>>
>>>
>>>
>>>
>>>
>>_______________________________________________
>>
>>
>>
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>>
>
>
>
>
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