Anthony Clay wrote:
SNIP
> Right now the PLL will generate the "base" frequency of .1 - 20MHz.  The
> resolution can be set by the PIC.  Because I can't find a TXCO (which I feel
> is necessary for this application) at a reasonable price, I have obtained a
> 100kHz crystal to use in an external reference oscillator.

You said your IF was 455KHz and you are receiving 0 - 200 MHz
you will ahave all sorts of problems if your LO has .1-20 MHz mixed in.
A LO of 200 - 400 mhz is what you need


> The signal can then be mixed with a signal from an XTAL oscillator that uses
> several xtals.  A specific frequency xtal can be selected by the PIC
> uProcessor.  This frequency is then mixed with with the PLL and then
> filtered (which is also selected by the uP).

Don't bother to generate the LO precisely, but rather measure and
feedback
to give you accurate receiver frequency, concentrate on making
the response linear (starting with a higher frequency and mixing down is
one
way)

Avantec make some nice TO5 type VCO packages with four pins, ground, +,
Control Voltage
and output (50 ohms +10 dbm)
I think they make a .9 - 1.8 GHz unit, mix this with 700MHz and you have
your LO
They will sweep their entire range in uSecs

The control voltage goes from 0v to 33 if I remember correctly but you
may get away with
0V to 5V

I sugest you use double balanced diode ring mixers ie. SBL1(1 - 500MHz
there is a version that will go higher) they are simple to use and give
good results

>
> The problem with this is that after about 140MHz there are no more xtals
> available.  So right now, I am spending my time trying to develop the
> world's most complex xtal oscillator.
>
> I have saved your email, and when the synthesizer is finished, I will post
> it on my web page and email you the address and post it here on the PICList.
>
> Anthony Clay
> zarthrag@intcon.net

--
Peter Cousens
email: p.cousens@cwcom.net  or  p.cousens@virgin.net
smail: 48, Yarmouth Cresent, London, N179PQ, England.