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to answer your specific question, sometimes connecting a non-50 ohm load will impact the phase noise, sometimes not. If your concerned about it you could connect to the main oscillator output thru:
1) 3 db pad, to guarantee a good load
2) connect oscillator to a buffer amplifier. Unless you are measuring a very low noise oscillator, the added noise of the buffer amplifier is probably not going to factor in.
You do not want a varying load! Lets say there is a long coaxial cable between your oscillator and the measuring system, and that cable is vibrating (fan noise, etc), it could be a big factor.
to answer your specific question, sometimes connecting a non-50 ohm load will impact the phase noise, sometimes not. If your concerned about it you could connect to the main oscillator output thru:
1) 3 db pad, to guarantee a good load
2) connect oscillator to a buffer amplifier. Unless you are measuring a very low noise oscillator, the added noise of the buffer amplifier is probably not going to factor in.
You do not want a varying load! Lets say there is a long coaxial cable between your oscillator and the measuring system, and that cable is vibrating (fan noise, etc), it could be a big factor.
there is nothing wrong with a cable, as long as it is not mechanically vibrating! The small movements of the cable can give rise to transmission phase noise.
Depends on how low a SBN you need to measure. I believe the Agilent PSA phase noise option is just a graded unit that has about 5 db lower SBN then regular unit. It is good for about -115 dbC/Hz at 10 kHz offset.
If you are needing to measure phase noise of a TCXO with -145 dbC/Hz spec at 10 kHz offset you need a signal source analyser like Agilent E5052.
It should be loaded as close as possible to the way it will be loaded in actual application.
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