Keyboard shortcuts

Press ← or → to navigate between chapters

Press S or / to search in the book

Press ? to show this help

Press Esc to hide this help

Your first receiver

Build an NFM receiver using the built-in signal generator. You will see its spectrum and hear a test tone without an SDR or antenna.

1. Open the signal generator

Start sdr– and open its interface. A fresh installation creates a workspace with three nodes:

  • a Device waiting for a radio;
  • a Scope already connected to the Device’s IQ output;
  • a Speaker waiting for channel audio.

On the Device node, choose Signal Generator (virtual). The device opens immediately and the Scope begins drawing a synthetic spectrum and waterfall.

If you do not see the starter nodes, create them from + Node. Draw a wire from the Device’s IQ port to the Scope’s IQ port.

2. Add a channel

Choose + Node, search for NFM, and add an NFM channel. Connect the nodes from left to right:

Device IQ → NFM IQ
NFM audio → Speaker audio

The patch applies as you work. If a channel says it has not been created, press Apply patch on that node.

Set the NFM channel to 300 kHz above the radio’s centre. The generator places an NFM carrier there with a 1 kHz audio tone.

3. Start audio

Use the Speaker node’s control. Your browser may require a click before it permits audio playback. Adjust the channel squelch if the tone stays muted.

4. Explore the interface

Try these next:

  • Drag the channel marker across the Scope to change its frequency.
  • Use the Device dial to retune the whole receiver.
  • Press [ or ] to change the tuning step, then use the arrow keys to tune.
  • Select a node and press p to pin its face to the Rack view.
  • Open Library → Templates to inspect ready-made FM, airband, ADS-B, ACARS, AIS, APRS, pager, PMR446, digital voice, ISM, and HF setups. Templates that require real off-air traffic still configure the signal generator, but their decoders will remain quiet.
  • Add a Recorder and wire the Device IQ output into it to create a short SigMF recording.

The ? button in the top-right corner opens the complete keyboard reference.

Move to real hardware

On the Device node, choose Forget this radio, then select the attached receiver. Device controls are built from the capabilities reported by its driver, so gain stages, antennas, sample rates, bandwidths, and advanced settings vary by model.

Run sdrmm --doctor or press Check hardware on an unbound Device node if your receiver is missing. The hardware guide covers supported modules and USB setup.