Transmit and receive aerial systems *MUST* be resonant for efficient power
transfer and anything like sensible range.


         Russell



On 3 April 2013 08:58, David <lists@edeca.net> wrote:

> On 31/03/2013 16:16, Sean Breheny wrote:
> > As your message hints that you suspect, any structure that generates
> > changing electric and magnetic fields IS an antenna to some extent.
> >
> > However, you can design structures which work better as an antenna and
> > those which do not radiate as much power for a given input current.
>
> Thanks to all who have offered help, I left it a while before replying
> as I have learned lots from some of the interesting conversations.
>
> Previous research had led me to Fair-Rite branded ferrite rods, made
> from 61 material[1].  These have good permeability below 10Mhz and the
> datasheet describes "a high frequency NiZn ferrite developed for a range
> of inductive applications up to 25 Mhz".
>
> Right now I have made a simple system around 4 transistors/FETs [2]
> (crystal oscillator, buffer, modulation, power amp).  This was based on
> a ham design and the basic carrier & modulation works, delivering ~25mW
> into a resistor load from 3.3v PSU.
>
> Coupling this to a transmit "antenna" made of the ferrite such that I
> get good results from my passive pickup loop[3] is where I am now
> encountering difficulty.  From a few inches I get some small mV at best
> out of the coax connector.
>
> How would you suggest driving a small coil round a ferrite core such
> that it works well for magnetic induction?
>
> David
>
> 1 - http://www.fair-rite.com/newfair/materials61.htm
> 2 - https://dl.dropbox.com/u/55193788/Temp/2013-04-02%2021.45.35.jpg
> 3 - https://dl.dropbox.com/u/55193788/Temp/2013-02-26%2021.40.56.jpg
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