Oscillator
Measurements:

Here are phase noise plots for four different high quality 10 MHz     
oscillators. The best performer is the Ovenaire ovenized crystal      
oscillator (OCXO).                                                                  

The Flex-Radio SDR1000 requires a reference clock running at 200 
MHz.  When multiplying  the frequency of an oscillator the phase   
noise degrades by 20log(N).  Where N is the multiplication factor.  
Multiplying a 10 MHz reference to 200 MHz degrades phase noise   
by 26dB.  Figure 2 shows the measurements normalized to 200      
MHz by adding 26dB.                                                              

Close in phase noise limits a receivers ability to detect a weak    
signal in the presence of a very large nearby signal.  Such as an 
S9 +50dB signal 100 Hz away from an S2 signal.  Farther out      
phase noise (at the IF or detection frequency), may  limit overall
receive sensitivity.                                                               

Here you can see the 200 MHz VF161 SDR reference clock compared
to the normalized 10 MHz oscillators.  Figure 4 shows that past 900 
Hz the VF161 phase noise performance is as good a $500 OCXO.     
The VF161 performance is much better than I anticipated.  Hats off 
to Gerald for selecting such a clean oscillator!                               

Copyright 2006
John Eckert
k2ox

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