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.
Source: ZFM
