First SDR Signal: FM Radio Setup in SDR++

[Pavel]

Short answer: For the first SDR++ reception test, use a strong local FM broadcast station, WFM demodulation and a moderate sample rate. The goal is to prove the complete chain—device, driver, RF input, tuning, demodulation and audio—before moving to weak or digital signals.

Before you start​

• Use one strong, known local signal for the first test. FM broadcast is convenient in many countries because the expected modulation and audio are easy to recognize.
• Write down the receiver model, antenna, operating system, application and sample rate. If the result changes, this record shows which variable actually changed.

Step-by-step method​

1. Step 1: Select the correct source in SDR++ and choose the actual receiver from the source panel. Set a stable sample rate near 2 MSPS for an RTL-SDR-class device and press Play before changing display options.
2. Step 2: Enter the known broadcast frequency in the main tuner, select WFM and set the demodulator filter wide enough for broadcast FM, normally around 150 to 200 kHz. A narrow NFM filter will produce distorted or very quiet audio.
3. Step 3: Start with AGC off and moderate manual gain. Raise gain until the station rises clearly above the surrounding noise, then stop if unrelated peaks multiply or the whole band lifts without a better signal-to-noise ratio.
4. Step 4: Set squelch fully open, confirm the correct audio sink and volume, then click the signal peak so it is centered in the active channel filter. After audio works, save a bookmark with frequency, mode and bandwidth.

Concrete example​

If the local station is 100.7 MHz, tune 100.700 MHz, choose WFM, use about 180 kHz bandwidth and start near 25 dB tuner gain on an RTL-SDR. If the signal is already very strong, 10 to 20 dB may be cleaner; the best setting is where the station-to-noise separation is greatest.

How to judge the result​

Success means recognizable stereo or mono broadcast audio, a peak occupying approximately the expected WFM channel width, and stable reception after stopping and restarting SDR++. Save this as the known-good reference for later antenna and driver tests.

What to record​

• A useful first result is repeatable: the same station appears at the same frequency after restarting the application.
• Judge reception by signal-to-noise ratio and intelligible audio, not by how bright the entire waterfall looks.
• Change only one control at a time and wait several seconds before deciding whether it helped.

Common mistakes​

• Changing several hardware, software or RF variables at once, which removes the controlled comparison needed to identify the cause.
• Treating one autoscaled screenshot or one unusually good result as proof without recording the settings and repeating the test.
• Leaving NFM selected while tuning broadcast FM makes a valid station sound weak, clipped or distorted and can be mistaken for a hardware problem.

Final check​

Restart the receiver application and repeat the known-signal test with the saved settings. A beginner baseline is complete only when the same signal, mode and audio result can be reproduced without guessing.