[OKDXA] Dipole Antenna Question

Fri, 01 Nov 2002 16:20:03 -0600

Yes for a change I am glad I asked.
I have read about that type of tuneing, but not in that much detail.
The broad banded dipole is a wonderful idea.
Their are allot of antenna makers who claim that their product will do broad
band and don't.
The B&W adds a resister to the top of their folded dipole and sey its like a
squashed rhombic. bull sh!#.
The gears were working on the tuneing bit but got lost with the last bit.
Hopefuly soon I can get some poles in the ground.
We never know when a move is near.
Thanks again
.
PS: I put some DX wax on one side of my 2 meter vertical and get a wonderful
front to back ratio, hi hi

Jim   AD5KD

----- Original Message -----
From: "Nelson Derks" <[email protected]>
To: <[email protected]>
Sent: Friday, November 01, 2002 11:15 AM
Subject: Re: [OKDXA] Dipole Antenna Question

> > Okay I hafta ask.
>
> You're a brave man...
>
> > say our home brew ladder line hainging from the center insulater is
> > pruneable, and it is. Would their be any way to tune the little bugger
> remotly?
>
> As a matter o'fact... YES.
>
> In the case of the 40 Meter Extended Double Zepp presented earlier, there
> would be little need to adjust the tuned feeder once it's dialed in. EDZ's
> are very broadband and the antenna would likely cover all of 40 with an
SWR
> of better than 1.5:1 at the edges. It would also have a very wide sweet
spot
> of 1:1 SWR probably 250 kHz or so in width, and that's a big slice of the
> band. In the case of the 20 Meter EDZ I had on the air for about a year,
the
> SWR curve was like 1.5:1 @ 14.000 MHz, 1:1 @ 14.060 MHz (that's the steep
> curve at the low end) and it held a 1:1 SWR through 14.300 or so... At
> 14.350 MHz it was around 1.3:1. Fully plug & play across the band with no
> tuner needed. The pattern was a tight Figure-8 and it was killer into
> Hawaii.
>
> Why is this so much better than a simple dipole?
>
> The EDZ is nothing more than a three half wave Dipole with the center
> section pulled down into a non-radiating tuned feeder. Since we're dealing
> with three times the wire length, the percentage of change from pruning in
> QSY'ing is also cut by a third. The antenna tunes more broadly. You can
> think of the tuned feeder as a phasing line that times the half waves
> presented to the 1.25 wavelength radiating section. This sharpens the
> Figure-8 pattern for best gain perpendicular to the wire, and you can
slide
> the center insulator to shorten the top section to 1 wavelength tip-to-tip
> and lengthen the feeder accordingly. Then it's called a Doublet and has a
> slightly broader pattern. Take the ends of the Doublet and solder them
> together, arrange the wire into a square, triangle, or circle, and that's
> called a Full-Wave Loop. Are the gears between your ears starting to
> turn...?
>
> Now... Since we're tuning the total wire length and have discovered we can
> arrange some sections to radiate while others don't, let's take this a
step
> further: Imagine you have some yard space that can comfortably fit 100' of
> wire. No magic number here, it could be 85' or 112' just as easily.
> Calculate an odd number of half wavelengths for 10 Meters (by using 492 /
f
> in MHz) that comes out to more than 100' of wire. My calculator says 7
half
> waves come in at 120'. It also says 5 half waves are at 116' on 15 Meters.
> We build a 100' antenna with an 8' tuned feeder and prune it to resonance
on
> 15. Then we add an oblong box with relays inside. And lengths of ladder
line
> hanging below. A short piece of ladder line added should give us a match
on
> 10, a longer piece would add 20 Meters. Calculate ladder line jumpers as
> needed for the bands you like and you can tune your 100' antenna anywhere
> you want by switching a series of relays. For the truly mechanically
> inclined, there may be a spooling option with sliding contacts on bare
wire,
> or you could use a model train engine and call it The Lionel Antenna...
It's
> the concept that counts.
>
> (Hey, I think I just found the next advert for ShaZamaHamaTronics! Combine
> two popular geezer hobbies and you know someone will buy it!)
>
> The outdoor relay idea looked like a maintenance problem to me, and the
> pattern will vary from band to band, so I ended up with an Off Center Fed
> Dipole (Coaxial Windom) that uses ~137' of wire fed ~46' from one end
> through a 4:1 current Balun and tunes everything except 160, 30 and 15
> Meters. 75 Meter 'fone needs a little help from the antenna tuner in the
> rig, but otherwise it's plug & play all the way from 80 CW up to 6 Meters.
I
> could add a second pair of wires for 30 and 15 Meters, but I'm having
enough
> fun as is...
>
> Now, aren't you glad you asked?
>
> And... Yes... You could take a pair of 102" CB whips and feed them with a
> very long ladder line tuned until it resonated on 75 Meters. The
efficiency
> would be poor, but you'd probably make it out to Union City on a good
night,
> and that's all that counts... Or, if your call is KD5DLL, you can forget
the
> feeder and just use the CB whip on 27.185... Hellllooooooooooooooo
> Newfoundland!
>
> - AC5UP
>
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