RF Transmitter

I have been using a signal generator to send a 50KHz signal along the perimeter wire and it works very well. I need to replace this with a stand-alone circuit. This could be an astable relaxation oscillator although sending square waves through a large ariel could mean I create a lot of interference with harmonics so I believe a sine-wave oscillator is a better solution.

A colpitts oscillator looks like a good candidate for a transmitter as I can use a similar tuned circuit as the one in the RF Receiver and do not need to use custom tapped coils. I need the ability to tune its frequency of oscillation to match the receiver unless I'm lucky enough to have just the right components to hit the resonant frequency spot-on. This probably rules out a crystal oscillator so I need to be aware of drift but at 50KHz, I believe the oscillator should be pretty stable.

Colpitts oscillators are often used at frequencies of many megahertz and are typically wired in a common-base configuration although at 50kHz, common-emmitter should be ok. Therefore, I will experiment with the following circuit:

Resonance is calculated using this equation:

By making C1=C2, this simplfies to:

Using a 1mH coil and two 22nF capacitors give a frequency of 48kHz. This seems a good starting point although it may be necessary to adjust the capacitor values to more closely match the resonant frequency of the receiver (measured at 50.2kHz).