The elements are. Except I uninsulated the 20m reflector and director.
These are the longest elements and will control how long the boom plus
elements appear.
A careful modeling of tower, mast, C31 boom and 20m ref/dir shows the
self resonance at around 1750 kHz. Just what I need for 160m.
Also if the tower is loaded and those 2 elements are insulated, there
is a lot of high voltage across the insulators. Takes that extreme
high rf voltage away to the ends of the two 20m elements.
Similar concerns would apply to loading the boom, though I agree the
C31 is really short to load to 80. Maybe a 40 meter yagi like the
340N? Path from one tip through boom to another tip is 29+12+36+12+27
or some such. The two twelves are the linear loading. So you would
have 36' of radiator plus 80 feet of end loading. That's 116 feet, so
it's probably doable. The 340N would need something like a center tap
on the element jumper to ground on the boom to make it happen.
36 feet of radiator is going to have a very low radiation resistance
on 80, so all in all there's probably a much better solution going,
like an 80 meter half-sloper. And if you can't get it up pushing
110,120 feet plus, 80m on a loaded boom will STILL be a cloud-warmer.
73, Guy.
----- Original Message -----
From: <n4kg@juno.com>
To: <TOWERTALK@contesting.com>; <n7vm@lgcy.com>
Sent: Thursday, January 24, 2002 10:06 PM
Subject: Re: [TowerTalk] Loading C31XR boom for 80m
A full size 3L40 on a 48 ft boom would make a good candidate
for a matched boom antenna for 80M. A tribander on a 31 ft
boom is pretty small. It possibly could be done but the BW
will be very narrow and efficiency questionable.
Besides, aren't the elements of the C31XR also insulated
from the boom?
Tom N4KG
On Thu, 24 Jan 2002 "Bill Ralston" <n7vm@lgcy.com> writes:
>
> Anyone ever tried to feed the boom on a C31XR for 80m?
>
> I had been planning inverted vee on tower, but this might interact
> with the
> 40-2CD & C31XR I'm planning to put up near the top at 105 and 95
> feet. So,
> I got to thinking about the idea of using the boom on one antenna to
> try and
> get 80m. Although many have done such for 40, how about 80?
>
> The problem I see with the 40-2CD is that the driven elements are
> insulated
> from the boom, so this won't look very symettric (and won't get any
> capacitive loading from the driven elements). Perhaps the C31XR
> with it's
> longer boom (31' versus 22' of the 40-2CD) is a better choice. With
> all
> those elements it will have a lot of capacitive loading!
>
> -- Bill
> N7VM
>
>
>
>
>
>
>
>
>
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