Ok, you're not going to answer my questions and prefer to spoon feed
us information while we keep guessing. With all due respect, I don't
have the patience to interrogate you for basic information, especially
when you won't even bother to confirm my guesses.
I think I've mentioned this to you in previous similar exercise, where
you also provided the absolute minimum amount of ambiguous information
in your question and in followups. Please excuse the repetition. If
you want to get sane answer on usenet, you will need to provide:
1. What problem are you trying to solve? A one liner is sufficient.
In this case it would be "I'm trying to design an FM broadcast band
receiver that will provide an indication when a 19KHz pilot tone is
received".
2. What do you have to work with? What existing hardware, software,
programming facilities, devices, do you have available?
3. If for troubleshooting, what have you done so far, and what
happened.
Ok, It's now a standard FM receiver, probably with a 10.7MHz IF.
What you're looking at is something like this:
<
http://upload.wikimedia.org/wikipedia/commons/e/ec/Frequency_Spectrum_FM-Radio.gif>
Note the -6dB/octave rolloff from the de-emphasis network. By time
you get to 19KHz, there's not much left from the original modulation
to trash 19KHz. Note the highly visible 19KHz line. Looks like about
-6dB down from peak audio level. That should be easy to decode.
As I previously mentioned, with pre-emphasis, there's no garbage at
19KHz to worry about. If there are any harmonics of the audio, or
intermod mixes, fix your receiver as such distortion will never be
tolerated in a typical FM broadcast receiver.
Correct. The narrower the bandwidth, the higher the sensitivity. See
the typical stereo decoder chip for details. Tell me why you need
extra sensitivity when the above GIF file showing the audio spectra
shows rather fabulous SNR?
Think about an all digital solution. Most FM receivers are all
digital these days, including the cheap receivers found inside
headphones, cell phones, and music players. I'm not really very
familiar with them, but some of them have a 19KHz pilot tone decoder
that lights up a "stereo" light on the front panel. With luck, you
may not need to design very much.
--
Jeff Liebermann
[email protected]
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558