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Parasitic Oscillations - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

Post subject: Parasitic oscillations Posted: Tue Jul 26, 2005 7:15 am

Could someone suggest a couple of good references on low frequency parasitic oscillations in microwave amplifiers?


Post subject: Posted: Tue Jul 26, 2005 7:58 am

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany

Please try the following: ... /LNA97.pdf

Good luck!

Best regards,

- IR


Post subject: ThnxPosted: Tue Jul 26, 2005 8:58 am
Thank you very much for the reference. I will have a re-look at the biasing circuitry and the bypass capacitors in my circuit. From a practical standpoint, how would one determine (when testing the amplifier) if low frequency products were modulating the suply voltages?


Post subject: Posted: Tue Jul 26, 2005 9:25 am

If you know the bandwidth of your input modulated signal you can see if the voltage on various points (Base, collector) on the amplifier's circuit has AC components (With high-speed oscilloscope or with spectrum analyzer don't forget to use DC block for this measurement) if you see these components at these points, you can estimate by their magnitude if your bypassing is adequate or not.

Alternatively, you can inject 2 input CW signals with known offset between them and do this measurement.

Should you need more information, please let me know.

Posted  11/12/2012

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