ODP: thru zero VCO questions

[Roman Sowa]

And how can one make stable VCO running so high?
I mean if we want to tune it at, say, 50Hz (afer downconversion)
and have reasonable stability, it must run at 20050Hz, and no 0.1Hz
less. It's almost crystal stability...
Of course, such thing would be used only for deep modulation,
but how can we tune it anyhow?

BTW, better to put 'braking point at 40kHz (LO=40kHz, VCO=20..60kHz,
IF=20kHz..0..20kHz) which makes stability problem bigger.

Am I missing something?

Roman


-----Oryginalna wiadomooeæ-----
Od: mbartkow at ET.PUT.Poznan.PL [mailto:mbartkow at ET.PUT.Poznan.PL]
Wys³ano: 14 wrzeoenia 1999 16:04
Do: synth-diy at mailhost.bpa.nl; chordman at flash.net; don at till.com;
uzs159 at uni-bonn.de; harrybissell at prodigy.net
Temat: Re: thru zero VCO questions


Did you guys try to do it in a completely different way ?
This probably sounds very radio, but...

what about modulating the frequency of an ultrasonic VCO
and then shifting its spectrum down by the means of AM ?

Consider a V/oct VCO with a scale shifted by say 20kHz,
i.e. f=k*exp(Uin)+20kHz. You can freely do a FM as deep
as 20kHz without worrying about the thru-zero problem.
Then its output is multiplied by a stable 20kHz sine wave 
and filtered with a 20kHz lowpass in order to reject the 
hf artifacts. Of course, a sinusoidal output of the VCO
is used, otherwise higher harmonics would not retain their
proper relations, but the final output may be freely waves-
haped to your taste.


MB


--

Maciej Bartkowiak, PhD
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