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Author Topic: 27.940 MHz Data / Pager System With Constant "Idle" Signal 27940 kHz - Finland  (Read 856 times)

Offline R4002

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This signal appears when the band is open to points east of the remote receiver I'm using (which is in the UK).  So it could be from Europe, the Near East...or any number of other places.

While there are dozens of active paging systems on right now, this one is unique, or there are just a half dozen signals on top of each other at once.

Typical POCSAG paging signals with 3-4 kHz bandwidth, 8 kHz bandwidth, others with 10-12 kHz bandwidth.

The "idle" (constant) data signal is a MFSK data signal 6.5 or 7 kHz wide.  Center frequency.   There appears to be an amplitude modulated part as well, and a carrier or pilot tone.  Currently two signals, with pretty typical very small offsets from the center frequency.

27940.05 kHz
27940.15 kHz

I will try and get some video and audio recordings of the signal.  There's a lot of weird stuff on the 25-30 MHz band (yes, including non-ham stuff within 10 meters) and 30-50 MHz (I know, there's another forum for that).

1315 UTC time
November 8th, 2023

UPDATE:

This is likely out of Finland.  Noted activity on another 5 watt paging and data link frequency out of Finland - 27.760 MHz 27,76 MHz 27.7600 MHz, active at the same time as 27.940 MHz
« Last Edit: December 20, 2023, 1431 UTC by R4002 »
U.S. East Coast, various HF/VHF/UHF radios/transceivers/scanners/receivers - land mobile system operator - focus on VHF/UHF and 11m

Offline fe8769

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Hello

I have many POCSAG type on 26 MHz band these days in France . I can't decode one . I tried WCODE , Sorfmon, PDW . I have some local POCSAG frequencies , I can decode them.

Can someone succeeded ?

Offline R4002

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There appear to be many different paging protocols in use.  Some of these systems seem to be POCSAG and others just sound like POCSAG.

There is a lot of 26 MHz band activity too.  I use 26.695 MHz / 26.745 MHz (plus center frequency 26.750 MHz) as well as 26.600 MHz, 26.645 MHz / 26.655 MHz and center frequency 26.650 MHz and the 26.850 MHz, 26.900 MHz, 26.945 MHz, 26.950 MHz, 26.955 MHz, 26.960 MHz, 27.300 MHz, 27.350 MHz, 27.360 MHz and 27.505 MHz ones as band opening indicators.

Plus there's the 27.450 MHz system (or systems) that transmit a continuous carrier when idle, and the 29.800 MHz, 29.900 MHz systems.  The 29.8 MHz and 29.9 MHz systems are believed to be located in the Nordic countries.

I don't know where 27.9400 MHz is coming from though.

Update: 

At 1344 UTC I tuned in to 27940 kHz FM 27.94 MHz FM and the signal is there.  I'm listening via SDRs located in the UK. 

There are at least two different transmitters with a carrier or pilot tone frequency:

Weaker of the two is on 27940.07 kHz, stronger of the two is on 27940.2 kHz.   There's POCSAG underneath this unique data burst mode, plus voice QRM from 27.940 MHz LSB and UK FM CB activity 27.94125 MHz FM. 
« Last Edit: November 16, 2023, 1347 UTC by R4002 »
U.S. East Coast, various HF/VHF/UHF radios/transceivers/scanners/receivers - land mobile system operator - focus on VHF/UHF and 11m

Offline R4002

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Here’s a video showing the waveform on a waterfall

27.940 MHz Data Signal With POCSAG Paging Underneath UNID Datalink 11 Meter Band G8JNJ SDR 11/16/23
https://youtu.be/FN4LZUrpz9w

U.S. East Coast, various HF/VHF/UHF radios/transceivers/scanners/receivers - land mobile system operator - focus on VHF/UHF and 11m

Offline R4002

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Its popped up numerous other times when the band is open to the eastern part of Europe.  Usually the 26.945 MHz and 26.960 MHz data link frequencies are alive when 27.940 MHz is coming in. 

Seems like the 27.450 MHz FM carrier also comes in around the same time.  The other POCSAG paging frequencies, including 27.300, 27.350 and 27.360 MHz, among other in-band frequencies, also seem to pop up around this time.  Other interesting ones include the 27.845 MHz / 27.850 MHz and the offset frequency 27.848 MHz or 27.8475 MHz POCSAG signals and the 27.505 MHz POCSAG bursts, with 1-2 kHz offsets +/- from that center frequency.  Like 27.940 MHz, 27.505 MHz seems to have numerous different bandwidth signals on it.  Some of them are closer to the 6-8 kHz bandwidth, others are 14-15 kHz and others are 18-20 kHz wide (!!)
U.S. East Coast, various HF/VHF/UHF radios/transceivers/scanners/receivers - land mobile system operator - focus on VHF/UHF and 11m

 

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