It is probably worth mentioning, that if you build a near-field, magnetic induction, power transfer project, that there will be some RF present anyway. Those "escaping waves" would be of great interest to the FCC (or $local_governing_body). Meaning to say that, "It's not supposed to be RF" isn't sufficient to ignore EMI regulations. (If it's a hobby project, the alternate rule is, "don't get caught" : ) On Tue, Apr 2, 2013 at 2:07 PM, RussellMc wrote: > Transmit and receive aerial systems *MUST* be resonant for efficient powe= r > transfer and anything like sensible range. > > > Russell > > > > On 3 April 2013 08:58, David 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 an= d > > > 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 rang= e > > 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 > > -- > > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .