From: "Pedro Wyns" <Pedro.Wyns@emmaus.be>
Date: Wed, 18 Aug 1999 12:41:53 +0200
Subject: encoders...

on your excellent artice on stereo encoders I would like to add the following:
...even the best encoder with over 60 db of separation is worthless on a
non-suitable modulator.  Most modulators use high impedance (100 kiloohms) bias
resistors on the varicap diodes and the audio is coupled using a simular
resistor.  This in combination with the capacity of the varicap creates a low
pass filter and phase distortion from 1 kHz on...  one should use a modulator
with a low value resistor (2 or 4 kiloohms in series with a RF choke such as
VK200).  Failing to do so may render your 3000 $ digital encoder worthless.
Much stress should be pointed at this issue to all interested people trying to
transmit decent MPX signals...
...same with synthesisers, they must be slow enough so they won't act on the MPX
signal.

Pedro M.J. Wyns
ex-fm transmitter designer.