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Originally Posted by tINY
Did you guys use a 5 Hz oscillator and a mixer? If so, how did you filter out the base band?
Or was it considerably more complicated than a ring modulator?
-tINY
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Hi tINY
That's taxing the memory a bit but I believe it had a 5Hz oscillator with + and - phase outputs and these were fed into a pair of MC1495 linear four quandrant multipliers. The output of these was fed through a 5KHz low pass filter to the loudspeaker driving output IC. It had numerous filters to make it suitable for telephone use.
Here's a pdf of the multiplier
http://www.ee.washington.edu/stores/...ear/mc1495.pdf
PS It was designed for private 4 wire telephone lines but we also supplied a 2 to 4 wire hybrid in a little plastic box that had a pair of LO2567 transformers in it. The manner in which those transformers were wired was a marvel to behold!
