Do you need this to be continuously variable, or could you channelize
this? 600 ppm at 16 Mhz come out to 9600 Hz, so you need to hit about
+/- 10 KHz. DDS would make this pretty easy. Analog devices has some
chips that might work. Look for the 9851 on the AD web site. 
Failing that, you could warp a very high frequency fundamental
oscillator and mix down. If you were at 160 Mhz, you would only have
to warp +/- 60 PPM, which is acheivable. Then you could mix down to 16
Mhz by using a 146 or 176 Mhz Local oscillator. More complicated this
way. 


Good luck,

Dave Bengtson



On Mon, 9 Aug 1999 20:19:06 -0400, in  you wrote:

>Hello again,
>
>Was just wondering if any of you electronic gurus out there could help
>with a PLL problem.
>
>The problem is we need a PLL circuit which can vary freq. by about 1200
>PPM with center frequency at 16 MHz.  Problem is most VCXOs are
>manufactured to around 100 PPM or better.  A _poor_ crystall oscillator
>(which allows a lot of freq swing) is still not sufficient, and is even
>harder to control when it comes to introducing jitter.
>
>Any ideas would be greatly appreciated.
>
>Digital frequency sysnthesizers are being looked at, but we still need an
>analog circuit which works.
>
>Thanks,
>
>Vincent Deno