[sdiy] HF VCOs and tracking problems

[Matthew Smith]

Quoth Richie Burnett at 14/11/12 09:04...
> I'd put in a good word for Direct Digital Synthesis (DDS) technology.
>
> DDS chips are cheap, give outstanding frequency linearity, allow you to set
> the frequency to mHz resolution from DC to MHz frequencies, can change
> frequency at the drop of a hat with no "settling time" and the output drift
> spec is as good as the crystal you use for the master oscillator!  These are
> gradually replacing PLLs in conventional frequency synthesiser applications
> because of their improved frequency agility and fine frequency resolution.
> They're also easier to set up than a PLL - No messing about with loop
> filters, stability calculations etc.

Any favourites you'd care to share?

> The only downside might be that you have to program in the frequency
> digitally over SPI.  This might complicate your application if it's all
> analogue so far.

Although, if you do have any digital, SPI is about as simple as you can 
get, even if you have to bit-bang it!

What's the actual frequency accuracy like? From what you say, it sounds 
like they're very "true to themselves." Or do they use a crystal, so as 
good as is the crystal?

Cheers

M

-- 
Matthew Smith

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