TopBand: "trapped dipole"

[Fred Hopengarten]

From:
Fred Hopengarten, K1VR
Six Willarch Road * Lincoln, MA 01773-5105 * 617/259-0088
e-mail:  k1vr@juno.com
Big antennas, high in the sky, are better than small ones, low.



     K9JF wrote:
     
>>I need some ideas from the collected masses regarding a horizontal 
>receiving/transmitting antenna for 80/160.
>     
>Near the top of my tower at the 95' level, I have an inverted vee for 
>75/80 
>meters with a manually operated stub to change between the portions of 
>the 
>band.  When I built the antenna last year, I "cut" the supporting 
>lengths 
>past the insulators to be resonate on 160.  However, I would like to 
>devise 
>something that would allow me to switch from 80 to 160 without 
>manually 
>attaching a stub (it's hard to do this at night when it's dark!).

K1VR:  It's just an idea, but I use it.  Run parallel RG-59 to the top of
the tower.  Put the two center conductors to the 160 m dipole as 
parallel feeders.  Ground the two braids to the tower.

Use an antenna coupler in the shack.  You now have a dipole on 160 and
two half waves in phase (2.1 dB gain) on 80.  Want fast bandchanging? 
Two antenna couplers and a knife switch.
Even faster?  A DPDT relay and Top Ten Devices box.

Why parallel RG-59 instead of open wire feedline?  Because  you want to
run the feedline right up the tower and taped to the tower leg, which you
can't do with open wire feedline.

Ground the braid again in the shack and you've just put a tuned feedline
inside a Faraday shield.

Works for me. 

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