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

Wed Mar 1 14:28:59 EST 2017

Hi Erik,

It is certainly possible to use a separate filter in the feedline to 
each antenna.  For example, here's an article I wrote many years ago on 
how to homebrew your own:

http://p1k.arrl.org/pubs_archive/89595

Those filters are only good for 100W or so, but there is no fundamental 
reason they couldn't be scaled up to 1500W.  I haven't researched it, 
but I'm thinking there must be commercial equivalents as well.

Alan N1AL

On 02/28/2017 10:41 PM, Erik Basilier wrote:
> Alan,
>
> Thanks for your reply. Your approach would provide 40m capability to replace
> the 40m capability that my (Sommer) beam loses through detuning.
> However, I wonder how hard your tuner must work on 40? Enough to create
> substantial feedline losses when the tuner is in the shack?
> Anyway, I have another reason not to choose your approach:
> I am rebuilding my station to support SO2R, and it is tough to avoid
> interference between the two radios operating on different bands, especially
> 40 - 20 and with the antennas close together.
> I found to my surprise, before the QST review came out, that the Low Band
> Systems multiplexer and band pass filters (my setup includes 40m) eliminates
> the interference problem. However, this scheme requires that the antennas be
> on a shared feedline. With your approach the 40m antenna would no longer be
> on the same feedline as the higher bands.
>
>
>
> -----Original Message-----
> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Alan
> Bloom
> Sent: Tuesday, February 28, 2017 11:09 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] Using your tower as a vertical - 160 or 80
>
> 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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