From: Bruce Griffiths <bruce.griffiths@xtra.co.nz> Subject: Re: [time-nuts] Advice on 10 MHz isolation/distribution     (Clay) The calculation is useful to help eliminate amplifiers that will not meet the phase noise floor specs. The amplifiers that remain will then need to be tested/measured for their actual phase noise. Bruce I have been thinking about how to make the measurement.  I don't normally measure OCXO phase noise.  I buy them to spec and lock my synthesizer to them, measuring phase noise at microwave frequencies using an older Agilent E5500 system with an 8254 (?) signal generator reference, which is an older version of their 8257. I was thinking I could split an OCXO signal, run one path thru the amp, and then mix them together and put the IF output into the E5500.  I think I would need a phase shifter to ensure the signals are in quadrature at the mixer.  I guess if I had two OCXOs I could let the E5500 control the EFC port on one, it would then use it's internal PLL to lock the 'reference' OCXO to the 'DUT' OCXO/amp.

> I have been thinking about how to make the measurement.  I don't > normally measure OCXO phase noise.  I buy them to spec and lock > my synthesizer to them, measuring phase noise at microwave > frequencies using an older Agilent E5500 system with an 8254 (?) > signal generator reference, which is an older version of their 8257. > > I was thinking I could split an OCXO signal, run one path thru > the amp, and then mix them together and put the IF output into > the E5500.  I think I would need a phase shifter to ensure the > signals are in quadrature at the mixer.  I guess if I had two > OCXOs I could let the E5500 control the EFC port on one, it would > then use it's internal PLL to lock the 'reference' OCXO to the > 'DUT' OCXO/amp. The E5500 manuals will talk about residual measurements to some extent. When measuring an amplifier, you can indeed use a phase shifter in one leg, but be sure to use a well-filtered test source. If you use a low-end signal generator (or any broadband generator at all, really) you need to filter the broadband noise from it, or it will degrade the apparent performance of your amp under test. I measured a few MMICs with a 3048A system using this technique here: http://www.ke5fx.com/pnamp.htm ... and a simple common-emitter amp with a transformer here, courtesy of Bruce: http://www.ke5fx.com/norton.htm On the first page you can see the importance of the filter, even when using a decent signal generator. -- john, KE5FX