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 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.
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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.
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
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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.
Here’s an overview of its performance and capabilities based on user experiences and tests:
- The transmitter operates from 325 MHz to 3.8 GHz and has a bandwidth of up to 20 MHz.
- There’s no filtering on the output which means the transmit signals will have spurs.
- Max output power from the ADALM Pluto transmitter is +8 dBm
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.
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:
- The device requires a Raspberry Pi to operate.
- Radioberry can be turned into a QRP radio with this amplifier
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.
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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.
Related Posts
- Best SDR Antennas
- Best Software-defined Radio
- HackRF vs Pluto SDR
- HackRF vs RTL-SDR
- Best Portable Software-Defined Radios
- Building an FM Transmitter using SDR
