POCSAG Receiver

Receives 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.

UI Overview

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
• RSSI/Audio: Top bar indicates signal strength. Bottom bar indicates the audio level. The audio bar can be useful for tuning settings without headphones/speaker to hear the tone.
• Squelch (0-99): Sets the signal to noise threshold. 0 disables squelch. Higher values allow more noise. Should be set so that strong signals are clearly received without any dropped audio.
• Volume: Output volume for the received audio. Can be used to monitor received signal quality.

Information

• Decoder Status: Indicates the status of the decoder state machine. White: Idle, Cyan: Clear, Yellow: Waiting for message start, Green: Waiting for rest of message.
• Batch Count: Number of message batches that have been received. A batch has 16 codewords.
• Bits: Displays the bits that are being decoded into codewords.
• Sync: Green when the frame decoder has received a "sync" frame. Messages are not decoded unless a sync frame is found.
• Codewords: Shows the number of codewords in the current batch. When the bar fills, the batch is complete and is processed.
• Baud Rate: The detected rate of the current message. 05: 512bps, 12: 1200bps, 24: 2400bps.

Buttons

• Ignore Last: Enables "Ignore" mode for the last received address.
• Config: Enters the settings page to configure options.

Config

• Enable Log: Logs messages to the SD Card at "LOGS/POCSAG.TXT"
• Log Raw Data: Logs the batch codewords as hexadecimal. Useful for debugging decoder bugs.
• Use Small Font: Uses the 5x8 font in the UI to show more messages on the screen.
• Hide Bad Data: Don't show (or log) codewords that fails checksum validation.
• Hide Addr Only: Don't show (or log) codewords that don't contain a message.
• Enable Ignored Address: Don't show (or log) codewords sent to the specified address.
• Beta: Enable the new POCSAG baseband processor. The app must be restarted for this to take effect.
• Save: Save any settings changes.

NOTE: App Settings must be enabled for settings to be saved.

Message Display

Typical message:

12:34 1200 #432123 F2
This is a test message

Description (from top-left):

• 12:34 - Time: The time that the message was received (time from PortaPack).
• 1200 - Data rate: The data rate used to receive the message.
• #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