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PJL · 26th Feb 2009, 12:04 am

I've started off with an oscillator coil from a transistor and have now got a reinartz oscillator producing a pretty clean sinewave. The next step was to add a varicap to be driven from the sweep from the tek scope.

This looks easy I thought but it isn't. The varicap is coupled to the tuned circuit so it has AC on it. Too much AC and the varicap becomes forward biased. I am also guessing that if I don't keep all of the AC swing in the linear operating area of the varicap then frequency will change with amplitude.

I have AC coupled the sweep via a pot to set the sweep width and DC bias for centre frequency via a pot but the next problem I encountered is the oscillator amplitude drops badly when damped by even a tiny load (50K).

Do I have any hope at all using the reinartz oscillator design or am I chasing the wrong design?

26th Feb 2009, 12:04 am	#1
PJL Dekatron Join Date: Sep 2005 Location: Seaford, East Sussex, UK. Posts: 5,997	IF wobbulator design I've started off with an oscillator coil from a transistor and have now got a reinartz oscillator producing a pretty clean sinewave. The next step was to add a varicap to be driven from the sweep from the tek scope. This looks easy I thought but it isn't. The varicap is coupled to the tuned circuit so it has AC on it. Too much AC and the varicap becomes forward biased. I am also guessing that if I don't keep all of the AC swing in the linear operating area of the varicap then frequency will change with amplitude. I have AC coupled the sweep via a pot to set the sweep width and DC bias for centre frequency via a pot but the next problem I encountered is the oscillator amplitude drops badly when damped by even a tiny load (50K). Do I have any hope at all using the reinartz oscillator design or am I chasing the wrong design?