[time-nuts] Best way for generating 8994.03 MHz from 2899.00042272.....MHz?

[Lux, Jim (337C)]

On 8/16/09 10:19 AM, "Magnus Danielson" <magnus at rubidium.dyndns.org> wrote:


> Rich's proposal is very sound and similar to what I would consider. I
> just haven't toyed with DROs but should get my wet feet some day... also
> true for chip oscillators in that range.
> 
>

There's a company up near Lake Tahoe (California) (I think that's where they
are) that does a tiny (<1cc) YIG oscillator that would be interesting to
fool with.

The challenge in making a high performance synthesizer is not so much the
actual VCO (whether it be DRO or MMIC or YIG or whatever) but getting the
microwave frequency down to where it can be compared with the reference. You
can do a straight divider, but then, the number of divide ratios is limited,
because fast dividers tend to be powers of two, or, at best, small integers.

You can then PLL that against the output of a DDS.  (this is what we did in
a breadboard at JPL, mostly to test out the parts, more than as an actual
design.. Hittite was developing (has developed by now) a GaAs MMIC PLL for
this kind of application (basically a xN PLL where N is smallish (<100)).
Some of their VCOs have an onchip divider too, which makes getting the
frequency down to where the programmable divider in the PLL chip can handle
it.

Or, you can use your quiet reference oscillator, and multiply that up to
somewhere near your microwave frequency, mix it with the microwave signal,
and use the output of the mixer as the input to your PLL phase/frequency
detector.

Or, you can use a sampling phase detector in your PLL (which requires a
hefty drive power, typically) driven by some DDS derived reference
frequency.  This is the traditional approach we (and others) have used in
deep space transponders in the past (without the DDS.. Driven by a carefully
hand tuned VCXO.. We did do a breadboard with the DDS approach, but we
couldn't get DRO tuning ranges over the whole 50-100 MHz we needed.)

Or, you can do a variety of mix and match schemes where you multiply a quiet
fixed frequency reference up, and mix that with some DDS derived output,
possibly itself multiplied up.

They all have different tradeoffs in terms of ultimate phase noise and
tuning ranges (and, of course, the usual issues of inloop and out of loop
noise contributions, etc.), as well as gain budgets, filtering requirements,
etc.