Esa Heikkinen wrote: > I also doubt that there could be something wrong with emitter follower > so I also did some tests with "capacitive coupler" build on bottom PCB > of the HP10544: > http://www.amigazone.fi/files/gpsdo/544coupler.jpg > (1 kohm. terminaton is not visible on the picture) > > Generally it's just a wire going over 10 MHz trace on the PCB and then > it's connected to the spectrum. By this way it's possible to measure the > output without loading it with any galvanic connection. Of course there > is almost 30 dB of loss but it's not any trouble with spectrum analyzer > having over -145 dBm noise floor. > > But with that kind of measure the output specrum looks like this: > http://www.amigazone.fi/files/gpsdo/544-5.png > > So there's less harmonics but 2nd and 3rd are still high if compared > with other OCXO's. Hard to say anything of higher harmonics because that > kind of coupler takes in all background noise like FM broadcasts etc. so > I wouldn't trust these measurements too much (and because of that I > didn't even mention them at first). > > Esa
The distortion now appears to be within specification. You cant expect much better given the 10544A internal buffer amplifier topology. Your can always use relatively high Q traps for the 2nd and 3rd harmonics if they are a problem. The best location for these is within your external low distortion buffer amplifier. It would seem likely that the scope measurements with a ~ 50pF load are misleading, try for a 10pF or lower load capacitance. Your external emitter follower also has significant distortion when driving a 50 ohm load. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
