"Mike Kaliski" wrote in
:


"John Smith I" wrote in message
...
Actually, old news from 3 years ago ...

http://www.eetimes.com/showArticle.j...cleID=21600147

JS

The guy doesn't even seem to realise that height is one of the prime
factors in optimising propogation, particularly at medium wave
frequencies and vhf. Building a tall mast costs plenty of money and if
commercial radio stations could broadcast efficiently from an antenna
the size of a bean can, they would have done it years ago.

This is surely just a couple of coils wound in opposite directions
with capacitive coupling and a capacity top hat to prevent coronal
discharge and maximise current in the top half of the antenna.
Basically a form of top loaded, inductively wound whip antenna tapped
somewhere up from the base in order to pick up a 50 ohm matching
impedence at the design frequency. I don't see any new or innovative
principles at work here.

Now if he could make it work efficiently on all frequencies with 50
ohms impedence and with no requirement for further matching or
adjustment of any sort, I would be impressed. :-)

The other day, just for fun, I modelled a shortened 80m dipole hung from
a 100-foot high supporting rope. The dipole was 35 feet long and had two
loading coils about 4 feet from each end. I fed it at the bottom end.

The thing would be fairly narrow and would require an autotransformer or
tuned match at the base (or a quarter wave open stub) but the PATTERN was
very nice, indeed. With all that current up that high, it's nice and
flat and low to the ground. Gain isn't spectacular, though, only about
1.5dbi. But phase 4 of them and you're up there with the big guns,
though probably only for about 10-20khz of the band.

And, on receive, it's a horizon-scraper. You'd hear stuff you didn't
even know was there before. Whether you can outshout THEIR local noise
and QRM is a different question, of course!



--
Dave Oldridge+
ICQ 1800667