[time-nuts] retry: PRS10 has spurious frequencies

John Ackermann N8UR jra at febo.com
Wed Apr 25 18:54:56 UTC 2007


SAIDJACK at aol.com wrote:

> Also, try making the sine wave of the PRS10 into a nice, fast edge rate  
> square-wave with a Fairchild NC7SZ04 driver inverter for example. The Wavecrest  
> units don't work as well with sine waves as with square waves. On the SZ04, put 
>  a 10nF cap in series to the input, and a 1 MEG resistor from it's input pin 
> to  it's output pin. Feed the chip from a very low noise 5V power source. 
> Insert a  40-50 Ohm resistor into the output path going to the coax. Put an  
> attenuator/AC-coupler into the coax so the Wavecrest doesen't get  overloaded by 
> the 2.5Vpp DC signal. Result: low noise comparator/buffer :)

And on the opposite front, the TSC-5120 isn't very happy with a square 
wave input, particularly if harmonics fall within its input range.  The 
symptom is lots of spurs showing up in the phase noise plots.  Adding a 
low pass filter with an appropriate cutoff helps a lot.

John




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