On Thu, 2012-08-16 at 09:15 -0700, Harold Hallikainen wrote:
> I can't provide a whole lot of info here, but here are some comments.
>=20
> I GUESS these are ceramic filters. They sound like they are for the sound
> section of an NTSC TV receiver. NTSC transmitted sound as an FM carrier
> with +/-25kHz deviation 4.5MHz above the video carrier. Since the video
> was transmitted using vestigial sideband (lower sideband suppressed below
> something like 1.25MHz), the sound carrier appeared to be the same as a
> 4.5MHz subcarrier on the video. Early TVs used a separate FM receiver for
> sound, but, for maybe the last 50 years or so, TVs used "intercarrier"
> sound where the audio was considered to be a subcarrier on the video
> signal. So, the complete 6MHz channel went through the video IF. An
> envelope detector demodulated the VSB AM video. The sound carrier then
> appeared as a 4.5MHz signal above the video. This was notched out with a
> filter before being sent to the remainder of the video circuitry (color
> demodulator, etc.). A 4.5MHz bandpass filter was used to pull out the
> sound carrier, which was then sent to the sound IF. Finally, the sound wa=
s
> demodulated using one of several types of FM demodulators. A common one i=
s
> the quadrature detector or discriminator. These used either a "quadrature
> coil" (parallel resonant LC) or a ceramic discriminator. That's what you
> have. I've used a ceramic discriminator with an SA639 to demodulate FSK
> data.

Hello Harold,

thanks for the info.

Would you happen to have a datasheet? I don't know what a "ceramic
discriminator" is. What of the other 3 filters? They can't all be used
for the same thing?

Thanks, TTYL

--=20
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