How do I wire a PKE antenna (inductive transmitter) ?

I bought this $5 PKE antenna

I've not opened it yet, but I'm sure it's simply a copper coil around a ferrite rod, optimised for 125khz.

I want my arduino to use this to send low-speed data a short distance (3 meters, undersea, hence my need for using LF induction).

How would I do this? I expect it needs an AC sine-wave current fed into it (resonator?) - how would I wire my arduino to transmit ? I expect a capacitor is needed in series, and the arduino needs to clock something that generates an approximately 125khz sine wave...

My receiver is a 3-axis inductive coil and parallel capacitor connected for now to an oscilloscope.

by cnd
September 19, 2018

1 Answer

Answer by mikerogerswsm

Difficult to answer without seeing the product. It may be a ferrite rod with a winding or it may be same with a C in parallel. Try driving it from a sig gen with a series resistor (say 1k) and see where it peaks. If it doesn't, add a parallel C, say 500pF and see where it peaks then. Try other values.

Driving it should ideally be sine wave but square wave will work. See ham radio mags for better matching circuits.

125kHz sounds rather high for undersea work, VLF, 3 to 30 kHz, is more usual

Alternatives include optical and acoustic.

+1 vote
by mikerogerswsm
September 19, 2018

Thanks! When you say "peaks", what would I be measuring? Current/Voltage driving it, or looking for a signal on my receiving coil?

The chips which drive these things have selectable output from 250ma to 1amp - so I'm guessing I'll probably need one or two transistors at some point.

Clever comment re VLF, and yes, any RF above "tens of khz" simply does not go through salt water - which is why I'm not using RF, but magnetic inductance instead. I also want only a short range; a bit like a personal-area-network for divers.

by cnd
September 19, 2018

Voltage driving it.

by mikerogerswsm
September 19, 2018

Not sure how a ferrite rod behaves as a magnetic inductor.

You may find it works without a capacitor.

by mikerogerswsm
September 20, 2018

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