POCSAG clearpath over AMPS

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POCSAG clearpath over AMPS
POCSAG clearpath.PNG
Frequencies 450450 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
0.45 kHzKiloHertz (kHz) 10^3 Hz
4.5e-4 MHzMegaHertz (MHz) 10^6 Hz
,455 MHzMegaHertz (MHz) 10^6 Hz455,000,000 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
455,000 kHzKiloHertz (kHz) 10^3 Hz
0.45 kHzKiloHertz (kHz) 10^3 Hz
4.5e-4 MHzMegaHertz (MHz) 10^6 Hz
455,000 kHzKiloHertz (kHz) 10^3 Hz
455 MHzMegaHertz (MHz) 10^6 Hz
Frequency Range 450 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).0.45 kHzKiloHertz (kHz) 10^3 Hz
4.5e-4 MHzMegaHertz (MHz) 10^6 Hz
- 455 MHzMegaHertz (MHz) 10^6 Hz455,000,000 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
455,000 kHzKiloHertz (kHz) 10^3 Hz
Mode FMFrequency Modulation
Modulation AFSKAudio Frequency-Shift Keying
ACFAutoCorrelation Function
Bandwidth 12500 KHzKiloHertz (kHz) 10^3 Hz12,500,000 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz).
12.5 MHzMegaHertz (MHz) 10^6 Hz
12,500 kHzKiloHertz (kHz) 10^3 Hz
12.5 MHzMegaHertz (MHz) 10^6 Hz
12,500 kHzKiloHertz (kHz) 10^3 Hz
12.5 MHzMegaHertz (MHz) 10^6 Hz
Location Chicago, IL
Short Description This was/is a special version of POCSAG developed by Ameritech Mobile Services in Chicago, Detroit, (now AT&T). It was primarly used as a 2 way version of POCSAG that allowed 2 way pager messaging. Not used much anymore as it was only used in the 90s and rapidly growing technologies and Ameritech being bought by AT&T shutdown many licenses.
I/Q Raw Recording
Audio Sample

remember the "possible APOC signal with multiple AFSKAudio Frequency-Shift Keying modulations" that was made too many months ago? Well, this signal could finally be identified as of now, as what is described in the short description.

This version of POCSAG was developed by Ameritech in the 1990s and was used to provide two way paging/text messaging in the form of rapidly switching of modes as seen here. It makes it harder to decode as all modes are AFSKAudio Frequency-Shift Keying modulated, and are variable length. The idle codewords remain the same though. However, baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. speeds, mark and space tones will vary.

There is one signal actually still active near the Chicagoland area, that is under an expired license. (hence this audio sample and image). Luckily, a good friend of ours was lucky enough to take a business trip down there to pick these samples up, with his SDR. He got some luck, thankfully. But the SDR almost had a hardware issue and didnt have enough juice to make a clear I/Q. But the audio from the scanner describes a better story.

If I got my analysis down correctly, here are all the modes based off of my research: And yes, my AFSKAudio Frequency-Shift Keying plugins for audacity can render about 80% of these modes:

1. 2200 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). tone. 2. 1200 hz tone appearing after the data bursts. 2. MDC1200. 3. 1300 hz mark, 1950 hz "middle", AND 2600 hz space idle tone, but the 2600 hz tone caused by distortion from 1950 HzHertz (Hz), unit of frequency, defined as one cycle per second (1 Hz). actual "space" being too strong. Therefore making the appearance of "3 tones". 4. 1300 mark and 2000 hz space with 1200 and 2400 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. detected (preamble and data). 5. 1300 hz mark, 1950 hz middle, AND 2600 hz space for a preamble and 1200 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. data. 6. Possible 2400 and 4400 hz 2400 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. preamble and data?

7. 1200 and 2200 hz idle. 8. 1200 and 2200 hz 512 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. and 1200, and on rare occasions, 2400 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. preambles with data at their respective speeds. 9. And a teaser tone that cuts off the 1950 hz tone, therefore leaving the 1300 and 2600 hz at a rather short rate.

I/Q, samples and others will be linked here as soon as time can make room for me.

Additional images[edit]

POCSAG clearpath 2.PNG