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Subject: Re: Analog FM

From: "james holloway" <jimh54@...
Date: 1999-08-21

I've read about electronotes from time to time but am unable to locate any
of them. is there anyplace online that one may download them?

>From: "Douglas R. Kraul" <dkraul@...>
>To: <>
>Subject: [motm] Analog FM
>Date: Sat, 21 Aug 1999 10:01:30 -0400
>From: "Douglas R. Kraul" <dkraul@...>
>Sorry, I'm a lurker (But Paul can vouch for me)
>Analog FM's limitations are actually more basic then what was discussed.
>why all of the points are valid the most fundamental limitation of trying
>accomplish "DX-7 style FM synthesis) with conventional analog VCOs is that
>such a VCO is not capable of modulating "through zero frequency". This
>limits the modulation index to the less interesting lower range. For
>example, using a 1:1 carrier to modulator frequency ratio the maximum
>modulation index with a conventional VCO is 1. Unfortunately if any of you
>remember your DX-7 experiences the most interesting sideband evolutions
>start occurring above this figure.
>The reason for this limitation has to do with some pretty esoteric
>details but in a nutshell most VCOs can not "reverse on themselves". By
>this I mean that as the modulating wave drives the carrier's frequency
>toward zero Hz it can not force it into "negative frequencies". And yes
>these really exist, it just a 180 degree phase reversal on the waveform.
>There is a way of making a VCO that is capable of this performance and is
>something I discuss if anyone is interested. or you can just scan some old
>Electronotes issues in the issues around #63 I think for a good write up.
>Back into lurk mode.
>Douglas Kraul
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