POCSAG Receiver

With this app you can receive pager messages using the POCSAG protocol.

This protocol operates in the VHF/UHF bands using FSK modulation. More technical details can be found by following the links in the References section.

Display summary

Description of displayed information, starting from top-left:

• Receiver frequency, RF amplifier, LNA, VGA, RSSI and Channel indicators
• Phase, Bit/baud rate, Log checkbox
• Ignore address checkbox and address
• The lower area of the display will show the latest received messages.

Settings

• Frequency: Sets the frequency to receive pager messages on. Can be adjusted with the encoder thumb wheel, on-screen numpad, or loaded from frequencies saved on an SD card. 439.9875 MHz is the most popular worldwide frequency used by Amateur radio for POCSAG. Amateur radio POCSAG uses 1200bps.
• RF amplifier: (0 or 1): Enables/disables the internal RF amplifier.
• LNA gain (0, 8, 16, 24, 32, 40): Sets the LNA gain. Further information: Description of the gain settings
• VGA gain (0 to 62): Sets the VGA gain. Further information: Description of the gain settings
• Phase (Positive or Negative): Usually set to positive. Typically the FSK lower frequency designates a high bit. Setting the phase polarity to negative will invert this, so the FSK lower frequency now designates a low bit.
• Data rate (512pbs, 1200bps, 2400bps): Sets the baud rate (bits per second) of the received data. Typically older paging systems use 512bps, while newer systems use 1200bps or 2400bps.
• Log checkbox: Enable/disable logging of received messages to an SD card. This log can be found on the SD card root directory, filename: pocsag.txt.
• Ignore address checkbox: Used to ignore messages sent to the address set.

Message display

Typical received message:

12:34 1200bps ADDR:432123 F2
This is a test message

Description (from top-left):

• 12:34 - Time: The time that the message was received (time from PortaPack).
• 1200bps - Data rate: The data rate used to receive the message.
• ADDR:432123 - Address: The address of the intended pager recipient.
• F2 - Function: (0 to 3) Indicates the type or source of message sent (can be used to provide a category of sorts).
• This is a test message - Message: The message data displayed as ASCII.

References

The following resources provide more technical information about the POCSAG protocol:

• POCSAG - Signal Identification Wiki - Provides frequencies commonly used in different countries and regions
• POCSAG - WikiPedia