On 2013-04-02 22:07, RussellMc wrote:
> Transmit and receive aerial systems *MUST* be resonant for efficient=20
> power
> transfer and anything like sensible range.

Russell,

Thanks, this is helpful.

As for range I need ~10" max, I'm looking to use this for=20
identification & timing of small go-karts.

For the TX, I assume this means making a resonant tank with the coil=20
inductor and a matching capacitance?  I can measure various wound cores=20
with my Atlas LCR (so long as L is >1uH) and calculate the C to test=20
this out.  If I am on the wrong track here please say.

For the RX I am more confused.  Professional systems simply use a=20
length of wire buried in the track with a resistor at one end and a=20
black box at the other (which connects to a coax feed line).  I had not=20
considered whether this was "active" (like RFID) or completely passive. =20
Regardless the maximum length of the detection wire is around 20m, which=20
doesn't seem like a highly tuned/coupled system!

My solution last year was a completely untuned inductor that I simply=20
saturated from a 9v battery.  The resulting mess of a spike (and ringing=20
afterward) was picked up by a passive loop and the gaps between these=20
measured to identify the transponder.  I am sure I can improve this=20
year, if only to stop polluting the local radio spectrum!

David
--=20
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