Graham,
I would be most interested on seeing the construction of your toroid
antenna. Any pictures?
I couldn't get mine to work until I had got the structure resonant and
designed a matching network for it. Resonance was determined by the
physical size of the coils and a home made air-spaced capacitor.
Matching was achieved using two capacitors in an Amega arrangement
(suggested by Prof James Corum, K1AON). Any possible coax feedline
radiation was suppressed with a common-mode choke (Very important if you
want to ensure it is the antenna and not the feedline that is doing the
work) . From this you can tell that my antennas were single band but
they exhibited a wide SWR bandwidth for such a small antenna.
All experiments on 14 and 21MHz were conducted using a mobile setup so I
guess the vehicle was part of the antenna system (ground). I had several
long SSB QSOs with VK and South America but the sunspots were kind in 1994.
My version would be impractical for LF. I tried to get a smaller single
coil version with end plates to work without success. I tried to get
feed impedance figures from G2AJV without success.
I do have a copy of Prof James Corum's European patent (13/01/1982), 52
pages of it, covering every conceivable toroid structure. One thing they
all have in common is that they are all resonant at the operating
frequency. The USA version appeared in 9/7/1980.
Regards
Peter, G3LDO
Yes , the counter wound construction was challenged during the
lecture and the concept of a mirror was introduced ... this then
negated any constructional / geometric problems , by simply using the
induced eddy currents in the metal plate to produce a virtual
'mirror' image of the coil ... an exact copy ... Thus the feed
requirements where reduced to one end of the coil and the back
plate ...
I made one based on the concept outlined during the lecture , 12
inch diameter coil , 3 inch x 3/16 pitch , resting on a 1/8 perspex
plate on a 3 ft diam alloy plate resting on a plastic dust bin . ,
fed with a short length of 450 ribbon cable via a air spaced
balum from a racal auto tuner , the results where quite odd , it
basically worked on all bands from 160 to 10 , the tuner achieved
a good match.
Running 150 watts , it gave good reports round Eu on 80 , 14
was very lively and a Russian found it quite funny that he was
getting a 10 over 9 signal on 10 mt from a garden bin .. even at
400 > 450 watts carrier power the ae did not flash over or heat
up ..how it worked ive no idea ! but the mirror concept seemed to
be the missing like that no one had though of .. im sure some one
at the lecture made a video of it ....
A very small 2 mtr one was also demonstrated , using 9 turns app
10 mm dial round a 10 mm former and a 100 / 75 mm disc ,
apparently he had used it mobile with good results. I have the
idea a 6 ft back plate with a 3 ft x 6 inch coil may work on
500 .. ive yet to find the 6 ft plate ....
Very sad to see he has passed on , as its possible a lot of his
later work may of been lost ?
G ..
--------------------------------------------------
From: "Peter Dodd" <[email protected]>
Sent: Tuesday, March 02, 2010 10:15 AM
To: <[email protected]>
Subject: Re: LF: 9kHz without high voltage
When I was technical editor at the RSGB in 1994 an interesting
article was received from Prof Jennison G2AJV on a toroidal antenna.
Before publishing it I felt that I should make one. This turned out
to be a problem but after several phone calls with G2AJV a 14MHz
version using two toroid coils and no end plates was made to work
The article was published in RadCom April/May 1994 'The G2AJV
Toroidal Antenna'.
After the article was published I continued to experiment with this
antenna. I also met Prof James Corum, K1AON at Dayton, who passed on
additional information on this antenna - he has a patent on the
toroid antenna.
Eventually my 14MHz version performed as well as a 14MHz loaded whip
antenna and the whole saga was written up in RadCom August 1994
'Evaluation of the G2AJV toroid antenna'.
All these RadCom articles are well illustrated with colour photos.
Regards
Peter, G3LDO
On 01/03/2010 19:56, Graham wrote:
Making a Torodial antenna, as presented at the Egham HFC
would be a good start .. the concept of the mirror differed
from the published articles ... I made one and oddly it worked
quite well at Hf ..how it worked ive no idea .how a 12 inch
diameter coil resting on a old no-entry sign (alloy plate) one end
fed with coax from the atu the other open achived qso's from
160 to 10 mtrs .. who knows .... .its still hanging in the shed
.. but a large one may work at 9 khz without the need for all
the coils etc ... Did anyone else attend the lecture ?.. it
followed the chap from Birmingham with a selection of loop
antennas . ....
G ...
NB .. Can anyone read this .. as '' design of toroidal reflector
..... Antennas '' is showing in the google search
http://www.informaworld.com/smpp/content~content=a770413350&db=all
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