VCO Phase noise: consequence for mixing...

Hi, there!
I'm new on this board, and maybe I'm veryy close to rules, so sorry in
advance!
My question, despite its simplicity, is rather head breaking: I'm
trying to understand and quantify the consequence of phase noise, due
to a VCO, when injected in a mixer.
As I think this phase noise could be assimilated as a coloured noise,
so a gaussian SPD, I don't really imagine what could happen going
through mixing process: a white noise??
Then, is it possible to quantify the consequence of this phase noise on
the mixer's sensibility?

Sure you could teach me some, and it'll be very kindfull.
Thanks in advance!

Mike

PS: sorry for my unperfect english!

Chromatik wrote:

> Hi, there!
> I'm new on this board, and maybe I'm veryy close to rules, so sorry in
> advance!
> My question, despite its simplicity, is rather head breaking: I'm
> trying to understand and quantify the consequence of phase noise, due
> to a VCO, when injected in a mixer.
> As I think this phase noise could be assimilated as a coloured noise,
> so a gaussian SPD, I don't really imagine what could happen going
> through mixing process: a white noise??
> Then, is it possible to quantify the consequence of this phase noise on
> the mixer's sensibility?
> 
> Sure you could teach me some, and it'll be very kindfull.
> Thanks in advance!
> 
> Mike
> 
> PS: sorry for my unperfect english!
> 
Your English is good enough.

Your question is technically outside the topics of this newsgroup, but 
may not be a perfect fit for any (sci.electronics.design may have been a 
good one to cross-post to).

Phase noise (and frequency drift) at the mixer LO port translates to 
phase noise (and frequency drift) at the mixer IF port.  This has the 
potential to cause two problems with your IF: your intended signal will 
have phase noise, etc., and unintended signals will be phase modulated. 
  Calculating the effect on your intended signal should be easy to 
calculate.  Less obvious is that if your desired signal is weak and 
there is a high-power signal that should end up outside of the passband 
of the IF the phase modulation could put that high-powered mixing 
product right in the middle of your IF, drowning out your desired signal.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Hi, and thanks, Mr Wescott, for your advice (cross posting in this
other group) , and your help.
Hopefully transistors works in a way that they produce the less PN and
drift as I can, but as the signal is low, the resulting signal suffers
from unsollicited modulations.
Now, it's time to go to the correct board :)
Thanks again,
Regards

Mike