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VK3ABK > TECH 15.04.07 13:06l 47 Lines 2262 Bytes #999 (0) @ WW
BID : 54651_VK3HEG
Read: GUEST OE7FMI
Subj: Re: A Different Dipole. (VK2TV)
Path: DB0FHN<DB0RGB<DB0AAB<DB0FSG<DB0MRW<OK0PKL<OK0PCC<OM0PBC<OK0PPL<DB0RES<
ON4HU<ON0BEL<ZS0MEE<VK4TRS<VK3HEG
Sent: 070415/1042Z @:VK3HEG.#WEV.VIC.AUS.OC #:54651 [Ballarat] $:54651_VK3HEG
From: VK3ABK@VK3HEG.#WEV.VIC.AUS.OC
To : TECH@WW
Hello again VK2TV and all.
Ray, VK2TV, has responded, with obvious delight, after I referred to his
'AR' article 'A Different Dipole'. Yes! That is the one, Ray. I just
retrieved the magazine and confirmed what I had done years ago. Very good
effort on your part; I didn't recognise you in print!
Ray wrote...
"I wrote an article for my local radio club newsletter in late 1982. The
article was picked up by the WIA and published in AR in February 1983
under the title of "A Different Dipole", using my previous callsign of
VK2BVO. The article was also published in "Break-In" in New Zealand. I
didn't claim originality for the design. I merely presented a different
view of an old design. A bit of lateral thinking."
I have just connected the dipole I made at the time (using RG8 coax) to a
70cm TX, and with a 'Revex' SWR meter, I find the dipole shows below 1.2:1
SWR from 432MHz to 440MHz. This antenna would have been made for 435MHz, so
you can see the good bandwidth properties of this design. I'm usually wary of
a direct coax feed to a 'balanced' dipole, and I haven't determined any effect
from the coax. But, as the SWR is so low, without any 'matching', it seems
that something is working as a 'conjugate' as Roger, G0CJM, has suggested.
My dimensions, calculated as I normally do, (300 divided by 432 X .95 and
divided by 2 to get a halfwave) gives the overall dimension. I have not
included a factor for the coax dielectic on part of the dipole. The .95 is my
usual allowance for 'end effect' (of the dipole). This would be allowed for
in Ray's equation, 'L = 299780 X k (or vf)' but I like to use basics.
So, my dipole dimensions are 31.5mm for the dipole and 115mm for each coax
section, with a 10mm gap at the feed point. You can see the diagram from
Roger, G0CJM, in Ray's bulletin to get the form of construction.
Thank's for reference, Ray, I didn't note the AR issue, just the memory.
As you say, this dipole would make a good driven element in an array, and
your ropable portable antenna is a 'doosy'! I hope that translates to WW.
I don't remember where I saw the criticism (I can spell it now!) of this
antenna, but it would have been in Ham Radio or QST.
73. Dick. VK3ABK.
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