70kHZ transmitter

[WM6]

If one need a 70kHz transmitter with exact frequency, I suggest this solution:

1.
Use this module from eBay ($38 + free shipping):

0.01- 5MHz DDS Function Signal Generator Module




http://www.ebay.com/itm/0-01-5MHz-DD...-/270864768941


2.

Signal generator has enough amplitude to act as transmitter you need, but if you insist that you need more power, then connect signal generator to this module from eBay:

Mono 25W Audio Amplifier Module Board, Based on LM1875



http://www.ebay.com/itm/Mono-25W-Aud...item5d30720799

Do not drive it with full power - 1/10 of max power, no more.

Inductance of antenna (ferrite core or air core - the last one is better) have to be about 50mH. Exact value depend of antenna windings stray capacitance. You need to connect antenna instead of loudspeaker.

Of course this transmitter can generate any other arbitrary frequency too (for some very different antenna inductance need to be recalculated).

Use sine wave.