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78 lines
2.9 KiB
Markdown
78 lines
2.9 KiB
Markdown
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---
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title: "Getting started with Digital Modes in Linux"
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date: 2019-09-04T09:52:21-04:00
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draft: false
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---
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This blog post is going to describe what steps I took to be able to decode signals using digital modes. Hardware wise, you will either need a RTL-SDR receiver or a transceiver radio with a cable plugging into the computer's soundcard.
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## Software Required
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- Gqrx (depends on GNU Radio)
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- This is if you are trying to work with RTL-SDR
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- It acts as a AM/FM/CW/etc demodulator for the data sent by the equipment
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- Fldigi
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- This is what decodes the protocol used to package the data
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- It acts as a modem and provides capability to transmit data using a transceiver
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- Pavucontrol
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- This connects both Gqrx and Fldigi if using RTL-SDR
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As you can see, if you are only using a transceiver then you can skip the parts mentioning Gqrx and Pavucontrol
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## Process
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### Gqrx
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When you first open up Gqrx, it'll ask you to configure the device. I have the RTL2832U, so if you have the same tool...
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Select the profile partially labeled RTL2832U. If you want to look at frequencies between 0 and 28MHz then add to the device string "direct_samp=3". Otherwise don't add that string.
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You can keep the rest of the settings the same.
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### Fldigi
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When you first open up Fldigi, it'll ask you for our operator info.
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| Field | description |
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| ----------------- | ----------------------------------------- |
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| Station Callsign | Your callsign |
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| Station QTH | City, State |
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| Station Locator | Your grid code. (Can look this up on QRZ) |
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| Operator Callsign | Your callsign |
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| Operator Name | Your name |
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| Antenna | Your antenna type |
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In Audio->Devices, make sure you select the physical device if you're using a transceiver, otherwise select PulseAudio.
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You can keep the rest of the settings as the default.
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### Pavucontrol
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Finally to link the two, run the following lines in bash to create a sink in order to push the audio from Gqrx to Fldigi.
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```bash
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pacmd load-module module-null-sink sink_name=MyLoopback
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pacmd update-sink-proplist MyLoopback device.description=MyLoopback
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pacmd load-module module-loopback sink=MyLoopback
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```
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Now open up `pavucontrol`. On the Playback tab, change the output device of GQRX to be "MyLoopback"
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On the Recording tab, change the input of fldigi to "Monitor of Null Output"
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## Conclusion
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Now the software is sufficiently setup to be able to receive and decode signals. Best of luck finding things out there!
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## Beginner Pitfalls
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Since I'm also a beginner, I will share what I got stuck on and how you can avoid it.
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Make sure that you know the appropriate mode to demodulate the signal. I've had luck getting information from https://www.sigidwiki.com/wiki/Signal_Identification_Guide
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-> This needs to be configured on both Gqrx and Fldigi
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