From: John Woodgate
Subject: Re: Why is Envelope delay distortion bad in AM systems?
Date: Tue, 17 Sep 2002 03:58:56 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Tue, 17 Sep 2002 06:55:04 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Tom
wrote (in <firstname.lastname@example.org>) about 'Why
is Envelope delay distortion bad in AM systems?', on Mon, 16 Sep 2002:
>I am looking for the "old fashioned" explanation as to why Envelope
>delay (or group delay) distortion is bad in Amplitude Modulation
>systems. I know what group delay is and why it is bad for digital
>communication systems (pulse distortion and all that). However, what
>difference does it make if the envelope of an Amplitude modulated
>waveform is delayed, when the modulating waveform is not pulse shaped?
>Or, better yet, if you have a delayed envelope (of an AM system), how
>does that relate to the mathematical definition of group delay, which
>is delta phase/delta omega.
Isn't this normally just a theoretical problem? If there is differential
phase across the spectrum of the modulated carrier, the recovered
modulation has non-linearity distortion. But in most practical cases,
the modulation bandwidth is very much smaller than the carrier
frequency, so the probability of getting much differential phase across
it is low.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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