[sdiy] Black Magic oscillator cans

[Tim Ressel]

--- Glen <mclilith at charter.net> wrote:
> I just visited the ECS web site and viewed the data
> sheets for a few of
> these devices. I also viewed the page about the
> dedicated programmer you
> would need to program these devices. Considering the
> need for a programmer,
> it seems somewhat expensive to get started with
> these devices, if you only
> need to program one or two it's going to be too
> expensive, but if you are
> doing thousands it wouldn't be bad.

Digi-key will do the programming, for free I think...
that is not clear either.

> There is one thing that bothers me even more than
> needing a programmer. I
> could not find any reference to the *Precision* with
> which these devices
> could be programmed. I could only find reference to
> the frequency ranges
> they would operate over. For example, if I want an
> oscillator set to
> 2.00024 MHz, can I actually program that particular
> frequency? It's
> possible that the closest frequency you could
> program would be 2.0002 MHz;
> or even worse, 2.000 MHz might be the closest
> frequency this device
> provides for. I would definitely want to know how
> fine I could adjust the
> frequency before I got into working with these
> devices.

This bothers me as well.

> If all you want is to feed a TOG, why not do what
> has been done
> commercially for several years. Use an LC oscillator
> containing a variable
> inductor. 

Interesting. But not totally precise. I gues you could
combine the two and use a DDS like the AD9831. That
way you get crystal stability, low jitter, and
adjustability.

> If you really want crystal stability, wouldn't it be
> fairly simple to have
> some custom crystals made? There are crystal houses
> that do this sort of
> thing all the time. I don't think it costs all that
> much, and it will
> probably provide you with even more stability and
> less jitter than these
> programmable devices. I know that most of the
> typical fixed-frequency
> crystal oscillators are not quite as accurate or
> stable as a good discrete
> crystal oscillator design, using a high-quality
> crystal.

Digikey used to offer a service like that. I went
looking for it in the catalog when I found the prog
oscillators. Custom crystal is another possibility. I
don't know what the price on that would be. But if the
prog oscillators work, then it seems $6 is reasonable.

--tr


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