Hi Jim,
So I just went through Rob's slide show. Seems to me he filled it with
enough technical information to impress the pants off a patent inspector or
radio newbie, but I'm not sure he has reinvented the wheel on this one.
I just bought an Anttron HM40W 40-meter whip (like the Lakeview Hamsticks).
Let me describe it's construction: from the mount up the fibreglas shaft is
a helix, running to about six or seven inches below the attachment point for
the stainless steel whip. Between the helix and the whip is a loading coil
to complete the loading for 7 MHz.
Sounds an awful lot like a DLM to me, and Hamstick-like antennas have been
on the market for years. (And work really, really well.)
It seems to me that his slide show reads a lot like Sevick from the 70s in
QST: W2FMI demonstrated that you can get excellent efficiency from shortened
antennas -- as long as you place them over lots and lots of radials. Sevick
also demonstrated the advantages of top loading, and experimented with
various forms of inductive loading, including helix, lumped inductance at
various points on the antenna and linear loading. I remember he had
excellent results from a 40 meter vertical that was less than six feet tall.
It had a huge top hat and enough copper underneath to upset world commodity
markets.
If anyone saw anything in that slideshow that's new, please let me know. It
certainly hasn't led me to believe the no-free-lunch rule about antenna size
has been repealed just yet.
73, kelly
ve4xt
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: "TowerTalk" <towertalk@contesting.com>
Sent: Tuesday, September 07, 2004 7:09 PM
Subject: [TowerTalk] Vincent loaded antennas
> I was following up on Rob Vincent's "miracle antennas" at URI. There's a
> fairly long slide show available from a link at:
>
> http://www.uri.edu/news/releases/?id=2659
>
> It's kind of hard to follow everything through this, but it looks like a
12
> foot high DLM (aka a partially continuously loaded monopole) has a
> bandwidth of about 150kHz at 7.2 MHz. This is nothing special, in my
> opinion, since it's only 1/3 the height of an unloaded regular monopole
> (which would have comparable bandwidth, depending on the physical
diameter).
>
> He also goes through a whole lot of stuff about the desirability of top
> hat, because it makes the current more uniform, but, again, this is
nothing
> new.
>
> I think Tom, W8JI, has a bunch of stuff on his website that goes through
> all the current distribution and tophat stuff (and Tom's is a lot better
> organized!)
>
> Rob Vincent did do some interesting stuff with measuring current profiles
> along the antenna (moving a donut type current probe over the antenna
along
> a track). I don't think he adequately controlled for the effects of the
> cables and such to his current probe, but it's hard to tell from the slide
> show.
>
> The slide show also changes the story a bit on melting the antenna. In the
> press release it sounds like it was accidental, but in the slide show it
> sounds like a deliberate test to destruction. Without actually having
> talked to Rob, I can say that the narrative in the press release could
have
> been a nicely juiced up version created by a PR flack. (been there, done
> that, read the story and thought, "I said that?")
>
> Jim, W6RMK
>
>
> Meanwhile, I am on a quest for small, reasonably efficient, rapidly
tunable
> radiators. In numbers:
>
> small == on order of 1 meter in size
> reasonably efficient = 50% would be nice (free space - ignoring effects
> from ground loss)
> BW has to be >10kHz (without retuning)
> tuning speed 1-10kHz/second within bands, several seconds for
> bandswitching. (that is, I'd like to be able to tune over a hundred kHz
> about as fast as I can turn the knob on the radio)
> Multiple bands (80-10 would be nice)
> Lowish cost (several hundred dollars each)
>
>
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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