[Elecraft] Using your tower as a vertical - 160 or 80

[Alan Bloom]

I use two of the top guy wires as an inverted vee.  There are insulators 
near the top of the guys and about 50 feet or so down.  The vee is 
brought to resonance on 80 meters with a center-tapped loading coil, 
which also acts as a balun.  The best match was with the coax tapped 
right about at the end of one side of the coil (and of course the coax 
shield to the grounded center tap).

Works great on 80 meters without a tuner and on 40 meters with a tuner.

Alan N1AL


On 02/28/2017 09:42 PM, Erik Basilier wrote:
> Years ago, after putting up a heavy-duty crank-up tower with several
> antennas on a tall mast at the top, I was interested in loading up the whole
> metal tree for 160 and/or 80. However, I didn't like the prospect of
> transmitted power getting back into the shack via the existing feedlines,
> causing all kinds of problems including losses. From a surplus vendor I
> obtained four square slabs of ferrite (no spec's) and taped them together to
> form a box-shaped common mode choke around the existing feedlines (and rotor
> control cable etc). I didn't have radials at the tower base, but a couple of
> long and wide copper strips buried and connected to ground rods to which the
> tower was grounded. I opened up the tower ground connection and I had a feed
> point. Finding resonance was not as easy as using my antenna analyzer. The
> signal from the analyzer was overwhelmed by picked-up broadcast signals,
> rendering the analyzer unuseable. I got by using a custom measurement setup.
> It turned out that the entire metal tree resonated in the broadcast band and
> was inductive at 160. I tuned it with a serial variable capacitor, and found
> the antenna worked very well on 160. However, I didn't continue using it, as
> I didn't feel safe not to have the tower grounded. I pondered schemes to add
> some kind of gamma-like matching device, but never got around to it. Also I
> never tried it on 80, but I suspect it would not been ideal for low angle
> radiation.
>
>
>
> Later I added more antennas to the mast, and with the added cables, the
> whole bundle would no longer fit in the makeshift ferrite choke. Out of
> curiosity I once again tried ungrounding the tower to check on its
> characteristics as a vertical antenna. I could no longer find the resonance
> I had seen and used before. Apparently, the ferrite choke had been a crucial
> part of the scheme.
>
>
>
> At this point I still don't have an antenna for 160 or 80. (I did try an
> inverted vee off the tower for 80, but it caused terrible de-tuning of the
> 40m part of my beam on the tower, so I gave up on that. Maybe I should try a
> sloper.)  I am thinking of putting up a dedicated vertical, but on my small
> lot it would couple to the tower. Perhaps it would be better to give the
> tower another look as my low-band vertical? My source of ferrite slabs dried
> up years ago. I wonder if anyone else on the list has used a similar
> approach and found a good way to choke off RF on a bundle of feedlines?
> Individual chokes don't seem very attractive to me as I have many cables,
> but if one has to go that route then it would make sense to look very
> carefully at the choice of chokes. I would also be interested in knowing
> about others' experiences with feed systems that leave the tower grounded.
>
>
>
> Thanks in advance for any useful ideas!
>
>
>
> 73,
>
> Erik K7TV
>
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