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Date: Tue, 02 Mar 2010 23:19:51 +0000
From: Peter Dodd <g3ldo@ukonline.co.uk>
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Subject: Re: LF: 9kHz without high voltage
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  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" <g3ldo@ukonline.co.uk>
> Sent: Tuesday, March 02, 2010 10:15 AM
> To: <rsgb_lf_group@blacksheep.org>
> 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
>>>