Talk:Radio-paging code No. 1

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Example file

I am unable to decode the POCSAG1200 message attached to the bottom of this page, is anyone else? (download/make/install multimon wget http://www.baycom.org/~tom/ham/linux/multimon.tar.bz2) Download the sample file: wget http://upload.wikimedia.org/wikipedia/commons/2/27/Pocsag-simple-stardado.ogg I converted the file from ogg to wav: oggdec -r Pocsag-simple-stardado.ogg Try to decode using multimon: multimon -a POCSAG1200 -t wav Pocsag-simple-stardado.wav No visible result. Any ideas? --ViceVirtue 23:20, 28 November 2006 (UTC)[reply]

The POCSAG transmissions use FSK with a deviation of roughly 4.5 kHz (actual deviation varies). Consequently, the channel bandwidth must be more than 9 kHz just to see the zero or one tones. The data modulation rate widens the bandwidth requirement. To faithfully turn the original FSK signal into an AFSK waveform, a bandwidth of more than 10 kHz should be used. I would do something simple such as map the center frequency to 10kHz and use a bandwidth of 20kHz.

IIRC, the POCSAG ogg file is sampled at 11 ksps, so its bandwidth will only be about 5 kHz. The result is one of the data tones is coming though, but the other is being lopped off by the anti aliasing filter. The result is an ASK waveform rather than an FSK signal. The multimon decoder probably cannot figure out what is going on. In a sense, the decoder software should issue a warning when it sees a sample rate of 11kHz. If the ogg file was upsampled when it was converted to a wav file, then the decoder would think the file was OK, but the ogg file had already destroyed the upper tone.

Glrx (talk) 20:09, 2 January 2011 (UTC)[reply]

I have replaced the example file with one I recorded as FLAC - this one does decode. I've also added examples for 512 bps and 2400 bps.

CubeTunnel (talk) 22:24, 30 March 2024 (UTC)[reply]

Orphan comments

Does anyone know where the official specification is?

There's a British Post Office specification

CCIR Recommendation R-584-1

Glrx (talk) 20:09, 2 January 2011 (UTC)[reply]

Is there any limit of length of message this standard allows to be send?