[sdiy] Help needed with AFVL

[James Patchell]

Boy, bet you get a lot of different answers to this one....

at 440Hz 1 cent is 0.26 Hz which is 0.06%.  Generally, 5 cents is about the 
limit you might want to see, so that would be 0.3% which is about the ball 
park you are in right now.

What you should really do is do a temperature run.  The tempco will only 
compensate for scale drift.  VCO's have two major modes of drift, scale and 
offset.  Scale drift is the one that is most difficult to deal with.

What you need to do is measure the frequency at to CVs and record the 
ambient temperature .  Then you need to change the ambient temperature and 
make the same two measurements.  I generally make the measurements 2 volts 
(octaves) apart.  And also, the more measurements you make, the 
better.  Then, doing a little math, you can calculate the scale tempco and 
the offset tempco.  Hopefully, you will find the scale tempco comes out 
very small.  Offset tempco will be caused by something within the 
oscillator itself.

If you are interested in doing all of these measurements, I can take the 
time to outline the procedures in more detail....I probably should do that 
anyway :-)

One of these days I need to finish the little tester I am building that 
will automate this process...


At 04:43 PM 3/29/2004 -0800, Peter Grenader wrote:
>(Acceptable Frequency Variation Limits).
>
>Dear Colleagues,
>
>I've got a VCO circuit I've been playing around with and finally got around
>to slapping a tempco in there for temp compensation.  SO far (an hour-ish),
>I've seen a .25% variance at 440 hertz.
>
>Naively I ask you - what's acceptable (%)??
>
>Not lab grade - but what's A good mean for our type application?
>
>I just need an idea to see how horribly bad (or good) this is and what to
>shoot for once I start noodling around for improvement.
>
>Thanks in advance,
>
>Peter

         -Jim
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