[time-nuts] About HP10544A

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Mar 9 19:47:30 UTC 2009

Esa Heikkinen wrote:
> Hi Bruce,
>> White emitter follower circuit attached.
> Here are the results. First, the circuit draws 33.3 mA at 12 vols. And 
> it's gain is 1:1 as expected with emitter follower - checked that with 
> RF generator as an input just to make sure that I built it correct.
> With HP10544A the output level is below +8 dBm:
> http://www.amigazone.fi/files/gpsdo/544-10.png
> (with 2 meters of RG174 and SMA-connectors between the circuit and SA)
> Now the harmonics look like this:
> http://www.amigazone.fi/files/gpsdo/544-11.png
> And 2nd harmonic level:
> http://www.amigazone.fi/files/gpsdo/544-12.png
> So the spec told that 2nd harmonic should be more than 25 dB down, it is 
> just in spec...
> So the final result looks that the 10544A is OK but it really has this 
> kind of output spectrum?

The distortion is about what one would expect given the buffer circuitry
within the 10544A.
Since retrofitting an improved oscillator circuit isn't really an option
you will need to filter the output to reduce the harmonic content.
Try a bandpass filter driven by the buffer and terminated in 50 ohms.

Should you retrofit an improved oscillator circuit you may as well
replace the oven controller to eliminate the oven switching frequency
related sidebands.


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