On Aug 20, 2010, at 4:56 AM, Grant Hodgson wrote: > You've come to the right place - well, that is if you want to devote a > significant amount of your life in the pursuit of ever-more accurate time and > frequency measurements....
:) > If you've only got one source then you need to use the frequency > discriminator method (aka delay line method) of phase noise measurement. > Basically you take the output of the source, split it in two, delay one of > the signals, re-combine the two and then measure the resultant signal on a > base-band spectrum analyser. [...] > The limitation of the frequency discriminator method is that the noise floor > of the measurement system is often worse than the DUT, especially if your DUT > is very good, and it's even worse if you're trying to measure close-in noise. > The Sherer article gives a good graph illustrating this. If you're trying to > measure the phase noise of the oscillator inside a Tbolt then I don't think > that a frequency discriminator will be sensitive enough, although I might be > wrong. I got the impression that for "good" OCXOs like the HP 10811 or (supposedly) the OCXO in my TBolt, the delay line method wouldn't provide enough sensitivity for measuring close-in phase noise. > Despite what you said, you might want to consider buying an HP 10811 > oscillator or similar which you could use in a phase detector measurement > system which is likely to give superior results. I might need 2 or 3 of them so I can weed out the under-performers! :) I had originally considered getting one of the surplus HP/Agilent GPSDOs with HP 10811 OCXOs, but I settled on the TBolt since it appeared to be almost as good (in terms of phase noise), a bit cheaper, and a bit easier to power than one of the HPs that need 48VDC. Well, I bought another power supply for the TBolt, anyway, but at least it would be easier to build a power supply that operates from +12VDC, a voltage that's always available in a ham shack. -- Mark J. Blair, NF6X <n...@nf6x.net> Web page: http://www.nf6x.net/ GnuPG public key available from my web page. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
