Phase Noise Plot to Equivalent C/N ratio conversion?

to

If I got it right : you have a ( phase_noise vs frequency ) and you want to convert this into a ( dBc vs frequency ) ?

What's "dBc" against mW ( and/or mV ) rms ?

to

of

Hi Paul,

First undo the "dB" operation, so you get "Noise power density (W/ Hz)" over "carrier power" ratios (W) versus frequency (don=92t convert to voltage ratios).

Integrate versus frequency over the required frequency span, and you have "noise power" over "Carrier power" ratio. This equals 1/(C/N) ratio. Make a good judgment on the skirts adjacent to the carrier to avoid that carrier power is assumed noise power.

Best regards,

Wim PA3DJS

) to

t of

Ok, this is exactly what i did. However, it's debated where exactly, is the cutoff frequency between the carrier and the noise.

It's actually really simple--the CNR is

CNR = 1/(2 (Delta phi)**2)

Cheers

Phil Hobbs

) to

t of

How do you define Delta phi? The change in phase?

How would you get this from a phase noise plot?

Sounds like you are talking out of your ass!

Suit yourself.

Cheers

Phil Hobbs

gmail/googlegroups, what do you expect ?:-)

...Jim Thompson

ts) to

ort of

rt

Hello Paul,

I assumed you did measurements with a spectrum analyzer (just scalar measurements, no vector based stuff). For determining "delta phi" you need a vector analyzer (or at least a quadrature down conversion setup).

You might change the RBW setting and look how the spectrum changes. Below a certain RBW setting, it will not change. In that case the skirts can be because of the signal's phase/frequency noise, or phase/ frequency noise from the analyzer.

When you have a known stable source, you might be able the measure the frequency/phase noise contribution from the analyzer. An indication of the analyzer's noise is the response at zero Hz.

I don't know your application, but noise very close to the carrier might be suppressed by your application (digital frequency tracking loop or just block length of the digital demodulation process?). Is it possible for you to derive the CNR from the output at some stage in you digital processing? Of course in that case the receiver front- end must be good.

Best regards,

Wim PA3DJS

sets) to

sort of

vert

ere

We measured this with a dedicated Agilent phase noise analyzer. It contributes very little to the phase noise in most cases.

Ok, you were on the right track by first converting the dBc/ Hz to a power ratio, and then integrating by adding these powers together. I have a basic MATLAB script that does this.

The real question is: where does the Carrier end, and the Noise begin, when looking at a phase noise plot? I'm sure it's dependant on your DSP processing, as some people have said that it's the phase noise outside of your tightest FIR filter that should be integrated, to get the total Noise.