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How can i measure the oscillator phase noise?

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John_li

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Hi all,
I want to measure the oscillator phase noise?Which point can i directly connect to avoid the mismatch or couple to measure?
Thanks,
John
 

I use Agilent PSA with phase noise option. The oscilator can be directly connected to the PSA.
 

    J

    John_li

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in ads in harmonic balanced you can in noise section calculate phase noise in any shape of this.
 
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.
 
biff44 said:
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.
Click to expand...
Thanks for biff44's kindness.I use SA to measure it.And how can i avoid the effect of the long coaxial cable as possible as i can?
 

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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