Stan,
Operating from my sailboat I'm restricted to horizonal antennas no more than
24' wide and supported in the middle from my mast. I've built a series of
single and multiband antennas for 40-10M and have used the bent end approach as
required with reasonable success. Success in my case meaning that I'm
competitive with the other LP locals using full sized dipoles at similar and
even higher heights.
I recently ditched the multiple dipole program since they were a hassle to
hoist and switched to a 40-10M Keleman 38' long unit that gives me 4 bands in
one antenna. I drop the ends just past the 20M trap.
KK4OBI has a full range of models and the related data on bent dipoles in
nearly every configuration at this link. Perhaps even the small losses
associated with that configuration are unacceptable in a highly competitive
station like yours, but the data suggests the losses are rather small and
perhaps equivalent to your proposed configuration if the bent section is <50%
of the length.
https://www.qsl.net/kk4obi/
GL - 73
Patrick, W7TMT
-----Original Message-----
From: TowerTalk <towertalk-bounces@contesting.com> On Behalf Of Tom Hellem
Sent: Sunday, December 22, 2024 08:34
To: Stan Stockton <wa5rtg@gmail.com>
Cc: TowerTalk@contesting.com
Subject: Re: [TowerTalk] A different dipole design
Simpler maybe is just drop the ends of the dipole straight down to make it fit
the available space?
I have done it many times and I don't believe there is any sacrifice in
performance.
It does require the total length of wire to be increased a bit.
73
Tom Hellem
K0SN
On Sun, Dec 22, 2024 at 8:09 AM Stan Stockton <wa5rtg@gmail.com> wrote:
> A few months ago I designed and my son built a 2L 40m Yagi using this
> type of design for loaded elements inspired by the W6NL style Moxon
> since that’s what he was going to build. The results are virtually
> the same in terms of gain, pattern, etc., but it is not as unwieldy
> and reduces the weight out on the element that causes it to sag
> excessively. TBD, but I believe it is less likely to interact with a 15m
> antenna.
>
> I have the need to put up a 40m dipole between a couple of towers here
> at ZF9CW. If the towers were about 20 feet farther apart I would just
> put up a flat dipole but they are a little close spaced for that. The
> element is going to be less than 50 feet long and it will be 50 ohm
> direct feed as opposed to about 75 ohms if it were just a normal dipole.
>
> For those who want to put up a dipole for any band, do not have the
> room for a flat dipole and do not want to either do some impedance
> matching with a 12th wave transformer or live with 1.5-1 SWR at best,
> here are the details of what I am going to find the time to do on 40
> meters. I will be limited to using the materials on hand. I would rather use
> #14 wire.
>
> 49 feet total (24-1/2 feet either side of center) of #16 wire fed in
> the center. At 15 feet out from center on either side there will be a
> 6 foot piece of 3/8” aluminum tubing that will be electrically
> connected in the center to the wire which will continue out for
> another 9-1/2 feet. So there will be 3 feet of aluminum tubing either
> side of center. From the ends of the aluminum tubing there will be
> #16 wires that will connect to the end of the wire (24-1/2 feet out).
> Those two wires should be ever so slightly slack so when the dipole is
> pulled up to its flat position there won’t be any significant stress on the
> ends of the aluminum tubing.
>
> If you just draw this on paper it looks like a dipole that is 20 feet
> shorter than a normal dipole and near the ends you have what looks
> like an arrow.
>
> I have this skewed a little toward the bottom end of the band, but
> about 4 inches shorter overall length would give you less than 1.5-1
> from 7.0 to 7.225.
>
> The gain of this dipole is about 1/4 dB less than a full sized dipole.
> Its bandwidth between 1.5-1 points is about 25 khz less than a full
> sized dipole but only if you do a perfect job of matching your 50 ohm
> coax to the higher impedance of the full sized antenna.
>
> I probably won’t do anything other than write this but if I get
> inspired I might sometime write it up for a magazine. I can see great
> benefit for those with limited space. A flat dipole is so much better
> than what’s commonly referred to as an inverted V.
>
> I’ll be glad to send an EZNEC file to anyone who wants to get a better
> picture of the design. Just send me an email.
>
> 73 and Merry Christmas.
>
> Stan, K5GO/ZF9CW
>
>
>
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