[time-nuts] About HP10544A

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Mar 7 16:23:49 EST 2009


Esa Heikkinen wrote:
>> New 10544A's have a somewhat cleaner output than that.
>> Perhaps something is wrong with the emitter follower.
>>     
>
> Sorry I forgot to say that the oscilloscope picture was taken directly 
> from HP10544A output, without emitter follower but with 1:1 probe, 
> output terminated with 1 kohm. resistor. With spectrum analyzer the 
> emitter follower is necessary due to 50 ohm. input impedance of the 
> analyzer.
>
> Datasheet of HP10544A claims that harmonics should be more than 25 dB 
> down. Doesn't look like they are.
>
> Here's a spectrum measured from OCXO which is used in the Thunderbolt. 
> I'm not an crystal oscillator guru but I think that this is just what an 
> xtal oscillator output should be:
>
> http://www.amigazone.fi/files/gpsdo/tbolt-1.png
> http://www.amigazone.fi/files/gpsdo/tbolt-2.png
>
>   
Esa

The capacitance of the 1x probe is too high.
Use a 10x probe with 1k across its inputs at the 10544A.
The 10544A output stage is an emitter follower.

Bruce




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