>
>> I also just got some advice from a ham friend who is also an
>> oscillator
>> expert. He suggested putting an LC parallel resonant
>> circuit at 14
>> MHz in
>> series with the sense line.
>
> That would reduce the currents in the line, and increase the
> impedance. Could be tricky since you'll need to keep the C
> low so as not to
> interfere with the sensing lines function (change of C equals
> change of
> state).
Actually, I haven't been able to have any capacitor interfere with the
sensing line function. I've tried all sizes of caps and none affect the
workings of the circuit. Since both the L and C are in series with the line
(parallel to each other), I think that just might do the trick.
>I think it'll also need to be a high Q circuit
> (Q>10) with a low DC
> resistance (you mentioned it quits working when a resistor is added).
Yeah, he suggested a Q of about 12 or so. You don't want the Q too hi as
that will reduce the RF bandwidth. He said I might want to de-Q it a little
by adding a resistor in parallel also. That shouldn't affect that sensing
ability since the resistor is in parallel with everything else.
>>
>> My friend says that one reason
>> why a choke may not work is that the choke has
>> capacitance between
>> the
>> windings. This capacitance then acts as a pickup for the touch
>> sensing line
>> and actually counteracts the effect of the choke.
> I think it has more to do with a change in capacitance. The
> distributed C is quite small so anything that changes the C
> even a tiny bit
> (like your hand being nearby) can have a large delta effect on C.
Well correct. Perhaps I didn't say it so well!
I am going to try some smaller chokes as well.
73,
Jon
NA9D
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