I think one of the biggest problems you might encounter is intermodulation
between mixers.

If a strong signal is present on any of the mixers, it will intermodulate
with the oscillator due to imperfect balance in the mixer. If these
intermodulation components get into the other mixer LO ports, it might cause
spurious responses.

Try to build some port-to-port isolation into the LO splitter, either
resistively (if you have power to spare), with a magnetic or LC 'hybrid' of
some sort, or vith individual buffer amps for each stage. If you choose the
latter, common base amps would be a good choice as they have very high
reverse isolation. Avoid ampliifiers with feedback, as feedback usually
ruins reverse isolation.


Joe
W3JDR



"MarkAren" wrote in message
oups.com...
Amongst other things it depends on the freq of the LO, the physical
distance between the SA605s.

What freq is the LO ?

How far apart are the SA605s ?

-Mark

On Mar 8, 8:18 am, wrote:
I'm designing a box that will use four SA605 receiver/mixer chips that
all need the same crystal reference. Even with all the good
application notes for the SA605, I'm not sure how to do this. Do I
build a Colpitts oscillator from transistors, buffer it, and then use
this output as an "external LO" for the mixers? Or do I connect up
the crystal to the SA605 oscillator pins as usual and then tap off of
this for the other chips? Using a function generator as an external
LO, I get the best results injecting a 300mVpp sine wave, if that is
useful.

Thank you!