Tuned coil
Tuned coil
(OP)
Hi
Can any one help??
I Have a tuned circuit which needs to be varible (25K-100K)
I've tried varactor diodes which only seem to go up to 100pF
which is not enough I need at least 2nF, is there a way of increasing the capacitance. Or a simple way of making a bandpass filter which is controled by voltage or resistance
Ive tried the semiconductor filters but they are to exspensive.
Many thanks for any help
DPJ
Can any one help??
I Have a tuned circuit which needs to be varible (25K-100K)
I've tried varactor diodes which only seem to go up to 100pF
which is not enough I need at least 2nF, is there a way of increasing the capacitance. Or a simple way of making a bandpass filter which is controled by voltage or resistance
Ive tried the semiconductor filters but they are to exspensive.
Many thanks for any help
DPJ





RE: Tuned coil
my memory says there is a cct used in power suppliies where a capacitor is used to bias a transistor. This gives you a multiplier effect for the capacitor. It would seem a logical extension that you could vary a divider cct to get an effective variation of the capacitance value. Put this into your filter cct and you should have a variable filter.
Now this is based on my memory and I cannot find a specific reference. But you should be able to find reference to it in books on power supplies.
How about playing around with an op amp (cheap one ) say lm741 or TL072
and a capacitor resistor cct on the feed back. This is how some of the tone controls are done in guitar amps.
Let us know how it goes.
Don
RE: Tuned coil
<nbucska@pcperipherals.com>
RE: Tuned coil
RE: Tuned coil
Good luck.
John Dunn
ambertec@ieee.org