Key Capabilities

The RTL-SDR is ideal for learning about the RF spectrum. Because the processing is done in software, you can visualize 2.5MHz of a band at once using software with a waterfall display, making it easy to spot signals that would be invisible on a traditional radio.

• Broad Spectrum Monitoring: Easily view large chunks of the radio spectrum simultaneously.
• Versatility: Used for general listening, satellite tracking, weather map reception (NOAA satellites), and decoding digital modes like those mentioned in our FT4/FT8 section.
• Cross-Platform: Drivers are available for Linux, macOS, and Windows, making it compatible with almost any SDR software.

Signal Data

There are two primary ways an RTL-SDR outputs signal data: Quadrature Sampling (the standard mode) and Direct Sampling (a mode that bypasses the front-end RF filters for receiving lower frequencies, i.e., 24MHz and below).

• Quadrature Sampling (Standard): Covers the primary range (~24 MHz to 1.7 GHz). This is perfect for VHF/UHF, FM radio, and aircraft communications.
• Direct Sampling (HF): Many modern RTL-SDRs (like the v3/v4) include a "Direct Sampling" mode. This allows the dongle to listen to the HF (Shortwave) bands below 24 MHz, allowing for global communication monitoring without needing an upconverter.

RTL-SDR Versions

There are two RTL-SDR Blog versions available now, v3 and v4. Version 4 is the latest but being relatively new it isn't as universally supported as version 3 just yet. You may have to install updated drivers for it to function correctly with older software.

The latest version (v4) features improved shielding, better thermal management, more sensitivity and better filtering. The v4 version is also available with either a USB-A or USB-C interface.

• Interface: USB 2.0 (USB-A, also available with USB-C)
• Lowest frequency: 24 MHz (below 24 MHz in direct sampling mode)
• Highest frequency: 1766 MHz
• Max receive bandwidth: 3.2MHz (but really only stable up to 2.56MHz)
• Price: typically in the $30 to $45 range
• Widely copied by many companies (the design is open-source).

RTL-SDR Sources

There are a number of different sources for RTL-SDR devices. The ones used in the STEMLab are sourced from RTL-SDR Blog. If you look at alternative RTL-SDRs, be sure and check their specs as these can vary depending on their individual implementation.

For those sufficiently interested the RTL-SDR is an open-source project so its schematics and hardware designs are made publicly available. That's one reason why there are so many copy-cat designs out there.

A note on RTL-SDR device availability: These devices use commercial TV tuner devices that have been out of production for some time. The RTL-SDR Blog folks managed to stock a large amount of these discontinued tuners but that stock is now running low. This has impacted the production of the new V4 SDRs. RTL-SDR Blog has modified the design and is producing a v4 Lite version. The availability of v3 devices doesn't seem to be a problem at this time.

Alternate Sources

Noolec also produces RTL-SDR type devices that are inexpensive and perform well. These should not be confused with cheap knock-offs that can be found on a lot of online sources.

Some Nooelec RTL-SDR Dongles.

Nooelec SmartSDR v5

Nooelec Nano v3

SDR Applications

The RTLSDR Information webpage in the References below lists many applications that can support these SDRs. These applications encompass a range of interesting topics and give a good idea of just how versatile this device is.

We also list information on some useful SDR applications here:
  ⓘ SDR Software Applications