EZNEC shows that this configuration is a barn burner for straight up
propagation providing about 4 db gain over a single dipole and much
attenuation at lower elevation angles. However EZNEC shows that raising the
antennas from 15' to 20/25 adds about 1 db of gain. NVIS articles and 1
book that I have read say
that the optimum height is about .2 lambda which agrees with my EZNEC
modeling. Raising the antennas also makes the input impedance a bit more
manageable.
EZNEC doesn't seem to agree with the "...theoretical gain of about 7db" as
it reports about 10 dbi?
It would seem that this configuration would be especially helpful in areas
with high ham populations--not so good in Wyoming, etc.
k7puc
----- Original Message -----
From: "David Jordan" <wa3gin@erols.com>
To: "Jim Miller" <JimMiller@STL-Online.Net>
Cc: "TOWERTALK" <TOWERTALK@contesting.com>; "Joe Barnes"
<n4jbk@bellsouth.net>
Sent: Thursday, April 07, 2005 7:14 AM
Subject: Re: [TowerTalk] 75 meter antenna
> Jim,
>
> I run a NVIS on 40m 2 full wave dipoles fed in phase just 15ft above
> the ground. Within the first 50-75 miles the signals are extremely
> intense. My station is an Internet remote so I actually operate about
> 50miles from the xmit antennas. Typically, I pin the "S" meter from 50
> miles away. The signals on 40m continue to be very strong up to about
> 350-400 miles, then a dipole at 60ft begins to out perform the NVIS. At
> around 350-450 miles the two antennas are about the same most of the
> time but when you get past 500 and well into 900-1000 the dipole at 60ft
> is about 20db stronger than the NVIS. So, the NVIS does do the job for
> closer in signals. The same would be true for 80m with the NVIS at about
> 25-30ft above the ground. The NVIS full wave elements are fed with
> homebrew 600ohm opern wire (in phase). The two elements are spaced a
> half wave apart (on 40 that is about 70ft). The theoretical gain is
> about 7db with a main lob angle of about 80 degree (straight up for all
> intents and purposes) omin directional.
>
> Another nice benefit of the NVIS is that it doesn't hear the foreign
> broadcast stations nearly as well as the dipole at 60ft.
>
> Your inverted V at 95ft would be great for DX but it's really too too
> high for short distance communications.
>
> Having both a NVIS and "V" at 95ft would be a lot of fun.
>
> 73,
> dave
> wa3gin
>
> Jim Miller wrote:
>
>>QST June 2002 Page 28 has an article for NVIS for 40 and 80. Should be
>>just
>>what you are looking for.
>>
>>73, de Jim KG0KP
>>
>>----- Original Message -----
>>From: "Joe Barnes" <n4jbk@bellsouth.net>
>>To: <towertalk@contesting.com>
>>Sent: Wednesday, April 06, 2005 8:33 PM
>>Subject: [TowerTalk] 75 meter antenna
>>
>>
>>
>>
>>>can anyone recomend an antenna for 75 meters that would be optimized for
>>>zero to about 400 miles? I am currently using an inverted vee with the
>>>apex at about 95 feet. I have 2 towers here , one is 100 feet the other
>>>is 125 feet, they are 100 feet apart.
>>>Thanks , Joe N4JBK
>>>_______________________________________________
>>>
>>>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>>>
>>>
>>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
>>any
>>questions and ask for Sherman, W2FLA.
>>
>>
>>>_______________________________________________
>>>TowerTalk mailing list
>>>TowerTalk@contesting.com
>>>http://lists.contesting.com/mailman/listinfo/towertalk
>>>
>>>
>>>
>>
>>_______________________________________________
>>
>>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
>>any questions and ask for Sherman, W2FLA.
>>
>>_______________________________________________
>>TowerTalk mailing list
>>TowerTalk@contesting.com
>>http://lists.contesting.com/mailman/listinfo/towertalk
>>
>>
>>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
> any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
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