Software Defined Radio SDR Transmitter

A Software Defined Radio (SDR) transmitter is a type of radio communication system (traditionally implemented in hardware with mixers, filters, modulators, etc.) that is implemented either in software or digitally.

While a traditional radio relies on physical components to process radio signals, an SDR uses software to perform these functions. The advantage is that they can be dynamically adjusted without modifying hardware.

Note that there are some components such as power amplifiers, RF mixers, RF Filters etc. that cannot be implemented in software.

A SDR transmitter therefore generally consists of both hardware and software.

In this article we review some practical software-defined radio transmitters

HackRF One

This is a software defined transmitter and receiver. The transmitter operates from 50 MHz to 6 GHz.

Nooelec HackRF One Software Defined Radio, ANT500 & SMA Adapter Bundle for HF, VHF & UHF. Includes SDR with 1MHz-6GHz Frequency Range & 20MHz Bandwidth, ANT-500, and 4 SMA Adapters

The block diagram of the system is shown below. All the system functions prior to the Mixer block MAX2839 are implemented in software.

The output of the MAX5864 Digital to Analog converter is an analog signal. Everything after this stage is considered hardware.

HackRF Block Diagram

The maximum output power from the HackRF is +15 dBm or 32 milliwatt. The output has two hardware filters U3 and U8 and therefore it will limit the harmonics in the transmit signal.

Notes:

  • HackRF needs either a laptop or Single Board Computer to operate

Pluto SDR

The ADALM-PLUTO (PlutoSDR) is a compact and budget-friendly Software Defined Radio (SDR) that’s particularly well-suited for educational purposes, hobbyists, and experimenters.

AD-EV8634-EBZ AD9363 ZYNQ7010 SDR ADALM-Pluto Active Learning Platform

Here’s an overview of its performance and capabilities based on user experiences and tests:

Notes:

  • HackRF needs either a laptop or Single Board Computer to operate

RadioBerry for Raspberry Pi

The Radioberry is a highly regarded Software Defined Radio (SDR) transceiver designed to be used as a Raspberry Pi hat. It’s especially notable for its use of the AD9866 chip, which provides a 12-bit DAC and supports a frequency range of 0 to 30 MHz with a maximum bandwidth of up to 384 kHz. The max output power is 20 milliwatt.

This makes it suitable as a transmitter for amateur radio applications within the HF spectrum.

AURSINC SDR Radioberry for Raspberry Pi 4 Radio Card Analog Devices AD9866&10CL025 12-bit Broadband Modem With 7in HDMI Screen LCD Display Monitor for Raspberry Pi 4 4B 3B+ 3B 3A+ 2B B+ Windows 7/8/10

One of the key features of the Radioberry is its affordability and open-source nature, making it an appealing choice for hobbyists and educational purposes. It has active community support and open-source software development.

Notes:

How does a Software-defined Transmitter Work?

  • Flexibility: The software in an SDR can be swapped out or updated to change the functionality of the radio. This means it can transmit across a wide range of frequencies and use different transmission protocols without requiring new hardware.
  • Processing: An SDR transmitter takes digital data from the computer, such as audio or other types of data, converts it into a digital form that represents radio signals, and then uses a digital signal processor (DSP) to modulate it onto a radio frequency (RF) carrier wave.
  • Output: After modulation, the signal is converted from digital to analog, amplified, and transmitted via an antenna.

Summary

SDR transmitters are highly versatile, capable of handling multiple frequencies and modes, which makes them popular in amateur radio, research, military, and commercial sectors for various applications. The adaptability of SDR also means it can adjust to new technologies and standards, making it a future-proof investment.

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