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MrBungle · 26th Jan 2018, 3:59 pm

I have built a quick VFO as a test case for measuring VFO drift. This is a simple Spectrum 2u6L coil, 27pF NP0 capacitor in parallel and 2x 330pF NP0 caps in a colpitts arrangement. There is a 2n3819 driving this and it uses a 78L06 as a voltage source. Driven from linear supply and monitored with a TF930 counter connected to the computer using some software I have written. This is all inside a cardboard box and the room temperature is a constant 19.2 degrees.

Getting slightly horrible drift on this as illustrated below:

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X axis is time in seconds. This is approx 34 minutes.

Does anyone know of any canonical references for tackling this problem as I evolve this VFO into something usable?

26th Jan 2018, 3:59 pm	#1
MrBungle Dekatron Join Date: Jun 2016 Location: London, UK. Posts: 3,687	Compensating for VFO drift I have built a quick VFO as a test case for measuring VFO drift. This is a simple Spectrum 2u6L coil, 27pF NP0 capacitor in parallel and 2x 330pF NP0 caps in a colpitts arrangement. There is a 2n3819 driving this and it uses a 78L06 as a voltage source. Driven from linear supply and monitored with a TF930 counter connected to the computer using some software I have written. This is all inside a cardboard box and the room temperature is a constant 19.2 degrees. Getting slightly horrible drift on this as illustrated below: X axis is time in seconds. This is approx 34 minutes. Does anyone know of any canonical references for tackling this problem as I evolve this VFO into something usable?