Created new POCSAG Receiver page

POCSAG-Receiver.md

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+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.
+
+[[img/screenshots/Receive_POCSAG.png]]
+
+# Display summary
+
+Description of displayed information, starting from top-left:
+
+- Receiver frequency, RF amplifier, VGA, LNA, 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](Hardware-overview), on-screen numpad, or loaded from frequencies saved on an SD card.
+- **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](Help!-Im-not-receiving-anything!---Receive-Quality-Issues#description-of-the-gain-settings)
+- **VGA gain** (0 to 62): Sets the VGA gain. Further information: [Description of the gain settings](Help!-Im-not-receiving-anything!---Receive-Quality-Issues#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 transmitted 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:
+
+```plaintext
+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](https://www.sigidwiki.com/wiki/POCSAG) - Provides frequencies commonly used in different countries and regions
+- [POCSAG - WikiPedia](https://en.wikipedia.org/wiki/POCSAG)