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Radio Tuner Notes.md
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Radio Tuner Notes.md
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# Radio Tuner Notes
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This is how frequencies in the FM spectrum are delegated
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| Label | Frequency |
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| --------- | --------- |
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| Min | 87.5 MHz |
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| Max | 108.0 MHz |
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| Step Size | 100 KHz |
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Since we cannot represent these values in the UI (using the dial element), we will instead use these values and multiply by $10^5$
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| Label | Frequency |
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| --------- | --------- |
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| Min | 875 |
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| Max | 1080 |
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| Step Size | 1 |
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## Message Format
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I think I would like to implement the GNU-Radio Script as a client server application that binds to some `localhost` port and can operate with the following messages
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| Message Format | Description |
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| -------------- | ---------------------------------------------------------- |
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| ?VER; | Outputs the current version of the server |
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| ?STATUS; | Gets the status of the program |
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| ?FREQ; | Queries the frequency that the program is currently set at |
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| :FREQ=%f; | Sets the frequency according to the float %f |
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| :QUIT; | Shuts down the server |
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To test out the server
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```bash
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telnet localhost 65432
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```
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## BUGS/ENHANCEMENTS`
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**Bug Fix:** Investigate different event handlers because the one that's currently used will send too many frequency set messages over to the server. (Maybe one that's like "when you release the dial...")
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**Feature Request:** Favorite radio stations section
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**Enhancement:** Listen again once the client closes the connection **[FIXED]**
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**Enhancement:** Allow multiple connections to the socket and have the server handle it appropriately
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**Enhancement:** Probably should more intelligently receive the number of bytes as opposed to setting it to an arbitrarily high number.
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**Enhancement:** Maybe use local sockets? (Nah, this will prevent me from having the Pi contain the radio and controlling from my laptop) **[INVALID]**
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**Bug Fix:** Send out full number instead of scientific notation. **[Not Needed]**
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**Bug Fix:** Include appropriate error messages for when the client can't connect.
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**Bug Fix:** Kick the client back to the connect screen when it disconnects.
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## Connect Screen
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In this screen the user can input the `IP address` and `Port` that the SDR server is hosted on.
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From there, it will confirm if it can connect successfully and if so, it will present the dial screen.
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There should be some sort of notification if the client loses connection. Maybe popping them back up into the connect screen.
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## Sending Audio Over the Network
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This requires the UDP Sink box in GNU Radio. Make sure you set the type to `float`.
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To hear the output do the following command:
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```bash
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netcat -ul address port | aplay -c num_channels -t raw -r sample_rate -f FLOAT_LE -
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```
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This tells netcat to listen to UDP on localhost:port and play it with ALSA with the above settings
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My current configuration
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| Name | Value |
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| ------------------ | ------------- |
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| Address | x.x.x.x |
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| Port | 7654 |
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| Number of Channels | 1 |
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| Sample Rate | 48000 |
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| Sample Type | Float |
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| Endiness | Little Endian |
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### Compressing Audio
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Command to convert the raw input stream into a ogg stream in standard output with a bitrate limited to 32 kb/s
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```bash
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ffmpeg -f f32le -ar 48k -ac 1 -i pipe:0 -f ogg -ab 32k pipe:1
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```
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## TODO
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So we should have the GNURadio program still act as a server to be able to change channels, but this time write the raw audio to a file descriptor from which ffmpeg grabs and compresses it to an ogg stream that gets transmitted over the network.
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Current command:
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```bash
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ffmpeg -f f32le -ar 48k -ac 1 -i pipe:0 -f ogg -ab 32k pipe:1 < raw_audio_pipe | nc -l 127.0.0.1 6003
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```
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Grab audio from named pipe that gnuradio is outputting to, then convert it to ogg and compress it with a 32k bitrate and then send that audio over the network.
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**TODO:** Convert the gnuradio blocks program to be a server again
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