Peter
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
--------------------------------------------------
From: "Alexander S. Yurkov" <[email protected]>
Sent: Monday, March 01, 2010 1:59 AM
To: <[email protected]>
Subject: LF: 9kHz without high voltage
I was wonder if it is posible to use a loop on 9 kHz. Serious problem
to radiate 9 kHz is high voltage we saw. Loop has that advantage that
voltage is not too high. Then i do some estimations. Let's assume
vertical
loop 15m x 50 m with 20 mm diameter coper tube as a wire. Then
effectivity
of such a loop on 9 kHz is about -65 dB. It is adequate to radiate 1 mW
on 9kHz (I=250A, TX power about 4 kW). We saw such a radiation should
give abt 100 km distance in QRSS. Besides such a loop is wellsuited
for 136 kHz. On 136 kHz it effectivity should be about -25 dB. Not too
bad: 1 W radiation with 400 W TX :-)
Regards,
Alexander
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