AW(Magnus): [sdiy] analogue phase modulation

[Magnus Danielson]

From: harrybissell at copper.net
Subject: Re: AW(Magnus): [sdiy] analogue phase modulation
Date: Fri, 12 Jan 2007 15:52:36 -0000
Message-ID: <380-220071512155236440 at copper.net>

> The other hidden feature is that the opamp
> will clip ay some constant level... you NEED
> a really stable power supply here

Actually no, not more stable than the VCO has. What you do care about is that
it is the same +/- 15V as the VCO and that the +15 V and -15 V is mirror
images around ground, but that you want anyway.

If you recall, most VCOs will reset their sawtooths as they have reached the
threshold which is typically set by a resistor divider of V+ -> ground. The
amplitude changes with V+ but not the frequency even if some modulations occur
during the shift. The scaling with the resistor will mimick that shift in
amplitude.

So, yes it depends on the voltage rails, but it should actually match the VCO
pretty well and that is the important thing.

MVH
Magnus