The mechanical considerations of mounting a 43-foot vertical topside on a
tower are considerable.
But the electrical considerations aren't trivial, either.
As I understand, without proper isolation of the feedline and elevated
radials from the tower, the entire structure could read either like an
end-fed long-wire antenna with most of its energy squirting off into space
or as an OCF windom array with much of the energy split between squirting
off into space and being driven into the ground.
The model I seem to recall, either by K9YC or W8JI, involved the feedline
running to the base of the tower to a choke and then up the tower to another
choke at the feedpoint.
The model, again, IIRC, seemed to suggest that a sufficient quantity of
tuned radials would auto-isolate themselves (in a manner similar to how the
15-meter elements of, say, an F12 C3 only respond to 15-meter energy), but
the choice of a 43-foot vertical suggests multiband operation. In that case,
you'd need multiple radials for each band of operation.
I tried to find what I thought was K9YC's tutorial on vertical antennas, but
it's either not on his website or it wasn't K9YC's.
73, kelly
ve4xt
On 11/1/12 7:28 AM, "Gene Fuller" <w2lu@rochester.rr.com> wrote:
> For anyone who is "trig challenged",, pencil, paper and a ruler and using
> about 8 feet to an inch (i.e.1/8th of an inch to a foot) would probably work
> out close enough. Anyway, trig wouldn't allow for any (though minimal ins
> this case) sag and wanting to throw in a little extra for tieoff and
> handling.
> Gene / W2LU
>
> ----- Original Message -----
> From: "Pete Smith N4ZR" <n4zr@contesting.com>
> To: <towertalk@contesting.com>
> Sent: Thursday, November 01, 2012 7:03 AM
> Subject: Re: [TowerTalk] 43 feet pole for vertical
>
>
>> There *is* no such thing as simple trig, if your last brush with a cosine
>> was 56 years ago! Fortunately, you can back this one out with the old
>> hypotenuse formula. Even I remember how to do that.
>>
>> 73, Pete N4ZR
>> The Reverse Beacon Network at http://reversebeacon.net, blog at
>> reversebeacon.blogspot.com,
>> spots at telnet.reversebeacon.net, port 7000 and
>> arcluster.reversebeacon.net, port 7000
>>
>> On 11/1/2012 3:35 AM, K8RI wrote:
>>> On 10/31/2012 11:00 PM, Hans Hammarquist wrote:
>>>> I was wondering if someone has experience with a 43 foot vertical,
>>>> mounted on top of a
>>>
>>> tower. I used one before on top of my roof, but that one was supported
>>> with simple guy wires.
>>>
>>> Needless to say that is not easy to do if I put it on top of my tower
>>> (85 feet tall).
>>>
>>> Any suggestion? Maybe it is a very stupid idea?
>>>
>>> Guying at 80 feet is almost as simple as guying when on the roof. I
>>> assume the tower is solid so use the same anchor points on the vertical
>>> as you would on the roof. It's just the ground guy anchor points have to
>>> be farther out.
>>>
>>> It only takes some simple trig to calculate the length of the guys
>>> assuming the yard is farily close to level. Use single or doubly braid
>>> poly. 1/8" is strong enough to anchor about 3/4 the way up the antenna.
>>>
>>> If the tower is 80 feet and the antenna is 43 then 2/3rds of 43 is
>>> roughly 28.6 feet (give or take a foot or two) So the height is 80 + 28.8
>>> is 108 feet. If the distance from the tower to the guy anchor is 80 feet
>>> then sqrt(108^2 + 80^2) and I don't have a calculator in there to run
>>> that last square root.
>>>
>>> I'd use double braided poly on the vertical and probably Phyllistran on
>>> the tower. However I think the 43 foot vertical is going to need radials
>>> so I'd use steel for those. I've done that with a 40 tower and 33 foot
>>> vertical and it worked just fine. I only used 4 radials but was pleased
>>> with the results. Course that was back in the late 60's until about 1980.
>>>
>>> 73
>>>
>>> Roger (K8RI)
>>>
>>>
>>>
>>>
>>>>
>>>>
>>>> Hans - N2JFS
>>>> _______________________________________________
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>>>
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>>
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