[TowerTalk] Vincent loaded antennas

[Jim Lux]

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)