[time-nuts] retry: PRS10 has spurious frequencies

SAIDJACK at aol.com SAIDJACK at aol.com
Sun Apr 22 18:17:30 EDT 2007


 
(Sorry, retry the attachement was too big for the list:)
 
In a message dated 4/22/2007 11:30:22 Pacific Daylight Time,  
henk at deriesp.demon.nl writes:


>Hello,

>The output spectrum of my just bought PRS10 has  spurious frequencies  
>from 580MHz in steps of 10MHz up to  680MHz. The 580MHz and 680MHz  
>signals just above the noise.  The 630MHz amplitude 60dB down the  
>10MHz. Does anyone know if  this a normal output?

>Henk




Hi Henk,
 
I have a expensive 10MHz ultra-low-noise Wenzel oscillator that we bought  
some months ago that has similar very nasty noise on it's output.
 
See the attached HP8563E plot, you can see the worst spur at 280MHz at  
-56dBm, which is about -50dBc/Hz!
 
The Wenzel has a measured phase noise floor of -169dBc/Hz at  10Khz.
 
In comparison, see our Jackson-Labs Fury GPSDO output measured exactly  the 
same way - one can only see the second and third harmonic everything else  is 
killed by the seventh-order low pass filter.
 
I asked Wenzel about this noise, and they said "we see it too, it's  caused 
by the HP8563E spectrum analyzer itself, we are not worried about  it".
 
Well, Wenzel went silent when I sent them the attached plots of an  MTI-230 
OCXO raw output, and our Fury GPSDO output both measured on the same  8563E 
setup. Never heard from them since.
 
I think the measurements show that it's pretty important to put a low  pass 
filter on the output of OCXO's.
 
I wonder what is generating such high frequency, high energy spurs in  these 
OCXO's.
 
bye,
Said 












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