Hi all,
I cannot seem to find any strong explanations for "residual AM", "residual PM", and "residual FM" in any of my electronic's books or Online. What are the causes and symptoms of these particular effects? Any help is most appreciated!
Thank You,
Bill
Beefy Logs! Did you serve them with Cheezy Poofs and Snacky-Cakes? ;-P
-- Cheers! Rich ------ "Do not rejoice in his defeat, you men, For though the world stood up And stopped the bastard, The bitch that bore him is in heat again." -- Bertolt Brecht"
instead of residual PM or FM.... look up "phase noise"
Mark
"residual AM" is the unwanted amplitude modulation when you frequency-modulate an oscillator. This can be because your FM is tuning outside the bandpass of some element or simply because of gain-bandwidth product for very wide deviations. You eliminate it by running the signal through limiter stages.
"residual FM" is the unwanted frequency shift caused as you attempt to do amplitude modulation. Cause is usually too much coupling of the modulation into voltage-variable-reactances in the tank. The solution is usually to add more buffering and isolation between the oscillator stage and the modulator stage.
"residual PM" is an unwanted phase shift as you amplitude-modulate a stage or as the input level to a discriminator changes. Solution is usually better limiting/isolation/bypassing/power supply regulation (this is often not too different than residual FM).
The above definitions of residual AM and FM are pretty much as described in old radio texts. Unwanted PM most often occurs in a comparator stage (boundary between analog and digital).
Tim.
Gee, I can't imagine that Google would fail in this arena.
Anyway, residual AM means that one gets some amplitude modulation of a signal when the intent was FM or some other type of modulation. This can happen when power supplies are not stiff or when the modulators (the circuits that combine the intelligence signal with the carrier signal) are marginal.
Residual FM means that one gets some frequency modulation of a signal when the intent was AM. This one is easier as it usually is caused by non-stiff power supplies.
QUAM modulators have some interactions and subtle effects that I cannot help you with here. QUAM is an acronym for Quadrature Amplitude Modulation. I am certain that you can Google for this.
Good luck!
Thanks Tim, Charles, and Mark -- very much appreciated!
Best Regards,
Bill
Incidental FM is FM due to AM, Incidental AM is AM due to FM! Residual is due to random noise and or hum
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