Re: Yo! RF dudes!

John Larkin <jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

[...]

> I've got a 50 MHz oscillator, using a 150 nH inductor, some fixed
> caps, a Maxim flecap (coarse tune), and a varicap (fine tune.)

[...]

> We can software compensate out the new TC, so the thing works, but
> I'd rather fix the inherent oscillator TC. If we apply a
> linear-with-temperature compensation voltage to the varicap, we
> can get a zero TC near room temp. But the varicap has its own,
> nasty TC that varies with capacitance, so this compensation winds
> up with a parabolic TC curve. OK, we could add a compensating
> polynomial in the software, if we didn't mind spending a week or
> so getting that right.

> RF requires a lot of patience.

> John

If the oscillator frequency is critical enough to require
compensation, why not lock it to a nearby crystal? You've already
got the varicap, why spend a week or so fiddling with compensation?

There has to be some crystal oscillator nearby. An hour's work
should get the divider and loop filter. Build, debug document and
ship in an afternoon.

You do this often enough. Why is there a problem in this case?

Regards,

Mike Monett
.

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