Using polystyrene caps and with the VFO not having any buffer stage the
device fed by a 9v PP battery drifts not more than 20 Herz in 30 minutes.

Frank GM0CSZ / KN6WH

What kind of battery is a 9v PP battery? And, it would likely be helpful to
know what the Inductor is that the negative temperature coefficient of the
poly cap is compensating for. Is that drift specification for the first 30
minutes after turn on or after the oscillator has been on for a couple of
days?

W4ZCB