In article , Stewart Pinkerton
wrote:
On Sun, 25 Jul 2004 17:13:33 GMT, "Fleetie"
wrote:


32ks/s (==16kHz bandwidth)? Isn't FM capable of up to 19kHz? ISTR
hearing that, or at least, that the difference signal (?) is stuck up
19kHz above the main signal.

Yes, it is, which means a 'brick-wall' filter from 15kHz to suppress the
pilot tone, since brick walls weren't so high back in the '50s!

IIRC It was common on some of the early stereo decoders to use notch
filters to kill the 19 and/or 38 kHz, combined with a relatively slow lpf.
This was a fiddle to set up for nulling the 19 kHz, but meant you could
avoid having a more demanding design to make on a production line.

Again IIRC the 'Toko' filters that were often used in the 1970's and 80's
also had an alignment that notched down at these frequencies to give
improved 19/38 rejection values without having to have ultra-high brickwall
cutoff for their LP slope.

By way of comparion, an old mono Leak Troughline I have leaks 19, 38, and
indeed, IF, like a sieve from its audio outputs. Filters? What are they?
Its got a time-constant. What more do you want?... 8-]

Slainte,

Jim

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