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how to KILL 50Hz signal:(

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liberal

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I have design a L-Band PLL,but there is a distinct spur at 50Hz,is it from power supply?I add 100u 10u 0.01u 10p caps at the supply,but no effective?can u tell me how to KILL the 50Hz signal?eliminate it.Thank u
 

Capacitors alone are not very efficient at low frequecies.
Try to connect 2 inductors , say 10-100mH, on both supply lines between power supply and your circuit ..
Also, if possible, put your circuit into metal enclosure and connect it to earth; this will provide some sort of shielding ..
Regards,
IanP
 

You may not be seeing power supply ripple. If your power supply is full-wave rectified, then the ripple is usually twice the AC mains frequency, or 100Hz.

Try checking for some easy problems:

Be sure you aren't injecting 50Hz via ground loops, such as two grounded instruments connected together with coax cables but plugged into different AC mains outlets.

Be sure your spectrum analyzer isn't creating the 50Hz spurs.

Try powering your RF circuit from a separate bench power supply to see if the hum disappears.

Be sure your project isn't too close to a big humming power transformer.
 

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