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[SOLVED] Phase noise degradation due to 50 Hz component from linear voltage supplies

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shashy.br

shashy.br

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Hi all,

I am planning to use a linear voltage supply for the RF chain (Transmitter , Receiver etc )

I need to know if the 50 Hz component at the input of the linear regulator ( 230V AC ,50Hz) will be present at the output of the linear voltage supplies ,

which will degrade my phase noise performance at 50 Hz offset from the carrier.

Please let me know if my assumption is wrong.

Also please let me know if there is any equation to find out the phase noise affects due to the Power supply ripple .
 
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Allays I use batteries when I evaluate phase noise of devices.
So use batteries, do the phase noise measurements, and connect after to the power supply and see the difference.
Phase noise degradation due to power supply depends by many factors, so is better to find first if is an issue.
 
You can not easily measure PN@50Hz off-set frequency and VCO PN@50Hz coming from VCO itself is more dominant than Power Supply Noise contribution.That's why, don't hesitate..
In additional to, modern voltage regulators have very good PSRR values ( for instance 70-100dB) @ low frequencies, so that power supply itself won't be any trouble..
 
capacitors are your friends. Use them often and everywhere.

Also beware of ground loops between the chassis and the earth ground of the 220v input plug.
 
If you use a bridge rectifier in the PSU then the ripple will be most significant at 100Hz rather than 50Hz.

Also, with some types of linear regulator you need to be careful of adding smoothing capacitors everywhere because you can cause 'big' transients on the PSU output with step changes in load if you slug the regulator response time using large capacitors.

These days it is pretty easy to measure phase noise or spurious at a 50Hz offset if you use a narrow detection bandwidth via DSP :)
 
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