SDR devices

About a decade ago, SDR devices where merely programmable tuners, i.e. tuners with an analog output signal, that could be fed into the soundcard of the computer. One of the examples - my first SDR device - the print from Elektor. No preselection, frequency range 0 .. 30 MHz and analog output, AD conversion by the soundcard, but lots of fun.

devices

For very long waves (i.e. in tens of KHz), an antenna in the input plug of the sound card might do (although it is adviced to decouple the antenna from the computer by using some transformer).

With the soundcard based systems, limitation is obviously the bandwidth of the soundcard. Most on-board soundcards where either mono, or limited to 96000 samples per second. While sufficient for e.g. AM, and even DRM, for e.g. FM one needs a bandwidth of at least 192K, not often available on an average laptop.

Last 5 to 10 years there is a huge amount of more advanced SDR devices on the market, devices with large bandwidths, high samplerates and enormous tuning ranges. Most devices now support a (selectable) bandwidth in the MHz, and a tuning range to 2 .. 6 GHz.

Examples of devices are shown in the picture below (there are many others, but these are just the devices I have)

  1. Top right, a LimeSDR in a yellow enclosure, with a receiver from 10 MHz to up to 3.5 GHz, and programmable samplerate. The limeSDR has next to being a receiver, a transmit option;

  2. the Adalm Pluto device, an SDR with a receiver range from app 70 Mhz to up to 3.8 GHz, and a samplerate of up from app 2.1 MHz. The Pluto can simultaneously transmit and receive. The Qt-DAB program - if so configured - is able to receive with the Pluto and transmit the audio in a selected service as stereo FM on a user selected frequency;

  3. two SDRplay RSP devices, the RSP Ia and RSP II, with a frequency range from a few KHz to 2 GHz, i.e. devices covering the lowerbands such as long waves, medium waves and short wave bands and samplerates from 2 MHz and up. With samples of 12 to 14 bits wide, these devices are pretty good for the things I do;

  4. The almost classic RTLSDR DAB stick, this one with an RT820 tuner. Of course, the device is less sensitive than others, output samples are just 8n bits wide, and the frequency offset is larger than that of some of the other devices;

  5. the HackRF One, a device with a receiver from 1 MHz to 6 GHz, i.e. also covering most of the lower frequency bands. The output samples are limited to 8 bits, but the oscillator is stable and the frequency offset small. As with the limeSDR, the HackRF has next to being a receiver, a transmit option.

  6. the Airspy (old model), a receiver with a range from 24 MHz to 1700 MHz, and a samplerate of 2.5 or 10 MHz.

Of course, such SDR devices can be used for more than just DAB decoding, I use them for e.g. receiving - and decoding - SW signals, ADB-b signals and FM, others use them for decoding GSM and WiFi signals.

devices