Before I start a search of the archives and the web I thought I would ask a
question that I think has been commented on here:
Is it possible to model antennas such as a Beverage or the bidirectional
off-center-fed antenna described by Tom Russell, N4KG, on page 192 of the
ARRL Antenna Compendium #7. Both of these antenna types have a height above
ground of about 8 feet (or less).
Using EZNEC I can see the pattern of the N4KG antenna OK, but the feed point
impedance he reports is not even close to what my model predicts. Also, the
gain is rather high (8-10 dBi) at relatively low angles (25-45 degrees).
Very attractive properties, but also very suspicious with respect to being
real. I am sure the antenna works as Tom describes, it is the model that is
puzzling.
Tod, KØTO
> -----Original Message-----
> From: topband-bounces@contesting.com
> [mailto:topband-bounces@contesting.com] On Behalf Of
> tsaitou@mta.biglobe.ne.jp
> Sent: Wednesday, August 25, 2004 10:47 AM
> To: topband@contesting.com
> Cc: dz@VOA.GOV; k6se@juno.com
> Subject: Re: Topband: Re: Feeding the tower
>
> Dear Earl,
>
> >.....coax feedlines and the rotator cable come down
> >all the way to the ground ..........
>
> I'm sorry for giving you my so-delayed question here.
> Would you let us know your idea how "rotator cable come down
> all the way to the ground",in fact?
>
> 73,Tosy - JE1TSD
>
>
>
> |To: dz@VOA.GOV, topband@contesting.com
> |Subject: Re: Topband: Re: Feeding the tower
> |
> |Andy, UA3AB wrote:
> |
> |"I need advise on how to make my tower to radiate on 160.
> |
> |Tower #1 is 42m (140 feet) high with 3 el short Yagi
> (Force12 Mag340N)
> |atop it, Another antenna 5m(15feet) above it is 3 el 30m short Yagi
> |(Force12 EF330).
> |
> |Another tower is 26m(90 feet) high with 6 el 20m and 6 el 15m Yagis
> |atop it. May be this is a better choice?"
> |==========
> |Either tower can easily be shunt fed using the single-capacitor
> |("gamma") method.
> |
> |My choice would be the shorter 26m tower because it will be close to
> |1/4-wave on 160m electrically with the top loading and therefore it
> |will have a wider 2:1 SWR bandwidth and less RF voltage across the
> |gamma capacitor.
> |
> |On my shunt-fed towers, I use either #8 AWG stranded wire or
> old RG-58
> |coax for the shunt wire. They are both about the same diameter and
> |their flexibility makes them easy to adjust. Some shunt-fed tower
> |users build "cages" for the shunt feed wire, which slightly
> increases
> |the 2:1 SWR bandwidth, but not enough to make it worth the
> extra cost
> |and effort, IMO.
> |
> |Rather than elevated radials, I advise that you use many on-ground
> |radials as the ground system.
> |
> |Also, make sure the Yagi coax feedlines and the rotator
> cable come down
> |all the way to the ground before they leave the vicinity of
> the tower.
> |
> |73, de Earl, K6SE
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