This Stereo encoder circuit built with MC1496.
It produces a very clean signal with good separation
(it performed as well as any other encoder, which
included some expensive professional ones) and has
been used on many professional commercial radio stations.
There's no input filtering on it so it has to be
proceeded by a 15 kHz low-pass filter (which was
something I put on my processor instead of on the encoder).
It needs a +/- 8 Volt supply but +/- 9V would work equally
well and it produces 1 Volt peak-to-peak into a 75 Ohm
load (and a bit more into a high impedance one) with 0dBu
audio drive. XL1 should be a 4.864 MHz one
The wires and extra PCB (off the top of the shot) in the
picture are for a composite clipper that was added afterwards,
which provides about another dB and a half of loudness.http://alectronics.blogspot.com/2010/05/fm-stereo-encoder-this-stereo-encoder.html