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Re: PLL Phase noise and SSB



The effect of phase noise on demodulating a signal is found by
integrating the phase noise over the frequency range of the modulation. 
So for SSB, phase noise at offsets between roughly 200 Hz and 2 kHz is
what counts.  A spec at 1 kHz offset would be much more meaningful than
one at 10 kHz, then.  

Typically, phase noise drops rapidly with increasing offset frequency,
but not always.  High-bandwidth PLLs can exhibit flat (or even
increasing) phase noise over their loop bandwidth.  That's one reason
why low-bandwidth PLLs are desirable in SSB receivers.  Of course, the
tradeoff is slow frequency switching.

73,
Bob KD1VV


Jon Ogden wrote:
> 
> on 1/5/01 11:23 PM, Frederick M. Spinner at fspinner@hotmail.com wrote:
> 
> > What is considered to be an acceptable and/or good amount of phase noise for
> > a narrowband SSB (or CW) receiver LO?  Also, is the proper measure point 1
> > KHz from the LO freq, or some other unit of measure, like "close in phase
> > noise"?
> 
> Boy it all depends.  Typically on VCOs that I sell to my customers, they
> spec them at 10 KHz from the LO.  But other people do measure closer as
> well.  I don't think I've seen anyone spec close in phase noise, but I've
> seen problems caused by it.  If I remember correctly, close in noise is more
> due to the internals of transistors in the oscillator than anything else.
> For example, while a BJT might give you good close in phase noise at 1 GHz,
> a FET will most certainly not.  FETs have horrible close in noise
> performance.
> 
> What's a good point for SSB/CW?  As low as possible?  :-)  I'll defer a
> better answer to someone else.
> 
> 73,
> 
> Jon
> NA9D
> 
> -------------------------------------
> Jon Ogden
> NA9D (ex: KE9NA)
> 
> Member:  ARRL, AMSAT, DXCC, NRA
> 
> http://www.qsl.net/ke9na
> 
> "A life lived in fear is a life half lived."
> 
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