I have a little PowerPoint (in adobe .pdf) I put together on my 160M shunt fed
tower.
Send me a e-mail if you want it and I will send it to you directly.
Seems to work OK. I tapped the tower to get close to a 50 ohm resistive load -
but not too important with an omega match. The operational-set frequncy of the
MonstIR on top of the tower totally upsets the tuning - of course. I retract it
when on 160 so I don't have to tune the omega everytime.
73, Bruce
--- On Sun, 4/25/10, wb6rse1@mac.com <wb6rse1@mac.com> wrote:
> From: wb6rse1@mac.com <wb6rse1@mac.com>
> Subject: Re: Topband: Fw: Shunt fed tower
> To: "Topband" <topband@contesting.com>
> Cc: "Wayne Rogers" <n1wr@chesapeake.net>
> Date: Sunday, April 25, 2010, 5:04 PM
>
> On Apr 25, 2010, at 7:10 AM, Wayne Rogers wrote:
>
> Obviously a 40' gamma match is easier to implement
> than a full height (90' in my case) shunt feed. Is
> there any benefit to
> going all the way to the top?
> _________
>
> I shunt feed my tower at the top of the bottom section,
> which is at 22 ft. The rod is 3/8 inch aluminum, 15 inches
> from the tower leg. I then use an omega match which obviates
> the need to search for the vertical sweet spot. My shunt
> feed works on 160 and 80 using latching relays to switch
> capacitors to change bands. This 22 ft feed point causes
> very high RF voltage across the omega capacitors which
> requires them to be vacuum variables. In addition to the
> voltage breakdown, the vacuum variables verniers make tuning
> very easy and precise compared to air variables. Attach
> point and distance from the tower leg will affect the values
> of the capacitors required, the RF voltage breakdown and the
> bandwidth vs SWR.
>
> It works. 173 DXCC on Top Band in 10 years from a very
> small West Coast USA city lot.
>
> YMWV.
>
> GL & 73 - Steve WB6RSE
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
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