All the building blocks to experiment and build radios
The RadioLab is an integrated laboratory system with building blocks to allow you to build and experiment with receivers for AM / SW / FM broadcast, ham radio SSB and CW bands. You can also build a transceiver with the RF Amplifier module. You can build direct conversion, superheterodyne, IQ Phasing type Software Defined Radio, and universal AM/FM/SW/LW fully integrated receivers.
The software is all open source so you can use it as is or modify it for your needs.
And there is a large prototyping area to allow you to design, build and test your own and integrate them with other building blocks.
The Direct Conversion receiver works as follows:
By using these components, you can construct a highly functional and interactive direct conversion receiver for the 40M band, with digital control over frequency and a user-friendly interface.
The following changes or additional components required for the superheterodyne architecture:
Additional Mixer and Local Oscillator:
Intermediate Frequency (IF) Stage:
Fixed-Frequency Local Oscillator for IF:
Variable IF Amplifier:
By adding these components, the superheterodyne receiver significantly improves selectivity and sensitivity over the direct conversion design. It can better reject adjacent channel interference and typically performs better in the presence of strong out-of-band signals.
Combining the Si5351 and an AM detector creates a functional basic spectrum analyzer.
This tool can be used for the following:
Utilizing the ESP32 as a frequency counter capable of handling signals up to 40 MHz is a remarkably efficient and cost-effective solution for the RadioLab. The ESP32’s built-in hardware timers and counters can operate independently of the core CPU, enabling precise pulse counting without significant processing overhead. This capability is ideal for measuring the frequencies of various signals.With the addition of dedicated libraries like
FreqCountESP, which streamline the frequency counting process, the ESP32 becomes an even more valuable tool. This flexibility and the high-frequency range make the ESP32 an indispensable tool for RF work for amateur radio experiments.
With just a few lines of code you can implement your own frequency counter and customise the TFT Display to suit your needs.
Decoding Slow Scan Television (SSTV) signals involves processing audio frequency tones that represent image data. The approach you’ve described utilizes a high gain operational amplifier (op-amp) and a Schmitt trigger to condition the incoming SSTV audio signal for digital processing by a microcontroller like the ESP32. Here’s a breakdown of how this works:
High Gain Op-Amp:
Interrupt on Rising Edge:
Frequency Measurement via Time Elapsed Between Interrupts:
This method of using interrupts to measure frequency is particularly effective for signals with relatively low frequencies, like SSTV tones, which are typically below 3 kHz. It allows for precise measurement without needing to continuously poll the input pin, which would be less efficient.
From Wikipedia. An image of a sunset sent as Martin M1.
By en:User:Little Professor, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9683443
Transmission of SSTV has not been tested yet but it is a trivial coding exercise.
If you are an experienced constructor / experimenter you already know the advantages of being able to concentrate on the circuit you are experimenting on and having a known working system to simply swap in and out your own circuit.
If you are new to construction or experimentation you can start off with the proven building blocks and get a feel for how all the different types of radios function.
You could start off by building an audio amplifier on the proto breadboard. A great starting experiment is to build a LM386 audio amplifier, then try a discrete transistor amplifier. The real beauty and what accelerates your learning is you only have to build one circuit. You have a working radio and you just swap your circuit in for the audio amplifier in the RadioLAB. Building audio filters using Op-Amps is not only a great way to learn but can make a profound difference to performance of a receiver.
Once you build up your confidence at audio frequencies you could start experimenting at RF frequencies. The breadboard is not ideal for RF frequencies but will work as a starting point so this is where the RF prototyping board is ideal.
Try a diode ring mixer, 4 diodes and two transformers. Compare your build with the professional ADE-1 RF Mixer. An RF amplifier could be your next challenge. A single transistor with passive components can give you 20dB of gain. The humble 2N3904, almost free transistor will work up to 30MHz.
You can add additional bands to the RadioLab with RF bandpass filters. Two transformers and a couple of capacitors is all that is needed. You can use the poor man’s spectrum analyzer included to tune the RF bandpass filters to match the band you want.
Crystal filters design is both art and science. You can build a CW crystal filter that really performs well with 3-4 crystals and a few passives. You can use the poor man’s spectrum analyzer included to match the crystal frequencies. By swapping your crystal filter design with the one provided you can compare the performance.
Designing oscillators is fun. There are many types but you could start off with a crystal controlled oscillator that acts as a BFO for the IF mixer. Once you have mastered that you can try a variable frequency oscillator and have a full analog setup.
Adding an AGC to the IF amplifier is another very interesting challenge. There is an option on the IF amplifier module to allow an external input to control the gain. You could start with an audio derived control signal and then do a IF frequency derived control signal.
At this stage you are mastering the art of radio building. You can take the individual blocks you have experimented with and build your 1st receiver, that’s all your own work. It’s unique to you and I have to tell you if you have never done this the feeling you get from achieving this is priceless. The only better feeling I have got from this hobby is when I build the transmitter side of this and put out a call and someone answers. It makes you feel like Marconi. It’s so good.
The SDR (Software Defined Radio) module processes the RF signals to audio output. The signal flow from antenna to speaker is as follows.
Antenna and Bandpass Filter (BPF):
Local Oscillator and Mixer:
Amplification and Filtering:
Digital Signal Processing (ESP32):
Digital to Analog Conversion:
Summation and Output:
You can design your own filters with the free software to suit your needs and you can also use the board to filter signals independently for use in Direct Conversion or Superheterodyne receivers.
The transmitter module is designed to interface with an ESP32 microcontroller. The ESP32 controls the module, through GPIO pins for keying the transmitter on and off.
Here’s the breakdown of the transmitter module’s functionality:
Si5351 Clock Generator:
40M RF Bandpass Filter:
Optional Plug-In Filter:
50 Ohm Dummy Load:
Digital I/O Interface:
The Universal Radio is based on the Si4735, the industry’s first fully integrated, 100% CMOS AM/FM/SW/LW radio receiver IC.
A patch is available allowing for the reception of ham SSB signals.
Some of the key features and functionalities of the Si4735 IC:
Digital AM/FM Radio Receiver: The Si4735 is designed to receive both AM (Amplitude Modulation) and FM (Frequency Modulation) radio signals. It can tune to different radio frequencies and decode the audio signals for playback.
Digital Signal Processing (DSP): The IC incorporates digital signal processing capabilities to enhance the quality of received audio and provide features like automatic gain control (AGC) and noise reduction.
Automatic Frequency Control (AFC): AFC helps in keeping the receiver tuned accurately to the desired station, reducing drift caused by factors like temperature variations.
RDS/RBDS Support: Many Si4735 variants also support RDS (Radio Data System) or RBDS (Radio Broadcast Data System), which can display additional information such as station names and song titles on compatible radio displays.
Built-in Antenna Tuning: Some versions of the Si4735 include a built-in automatic antenna tuning feature, which can optimize reception based on the received signal strength.
SPI/I2C Control: The IC can be controlled and configured using standard serial communication interface I2C (Inter-Integrated Circuit).
Analog Audio Output: It provides analog audio output for connecting to speakers or headphones.
Programmable Features: It offers various programmable features and settings to customize the radio receiver’s behavior to suit different applications and regions.
There is a built in 40M RF filter. The filter consists of two tunes circuits coupled together with a 10pF capacitor. The transformers are matched for 50 Ohm impedance. For other bands you can build these on the prototype board.
The RF Mixer uses an ADE-01. The ADE-01 is an RF mixer manufactured by Mini-Circuits, a well-known company specializing in RF and microwave components. Mini-Circuits is renowned for its wide range of RF products, including mixers, amplifiers, filters, and more.
Some key details about the Mini-Circuits ADE-01 RF mixer:
The RF Amplifier uses a BGA2815 Monolithic Microwave Integrated Circuit (MMIC) wideband amplifier which offers offers several advantages in various RF (Radio Frequency) and microwave applications:
Wide Frequency Range: MMIC wideband amplifiers are designed to operate over a broad frequency range, DC and 2.2 GHz, making them versatile and suitable for multi-band or wideband applications.
A Single-Sideband (SSB) crystal ladder filter is a type of electronic filter used in radio frequency (RF) and communication systems to selectively filter out one sideband of an SSB signal while rejecting the other sideband and unwanted frequency components.
Variable Gain IF Amplifier
The Variable Gain IF Amplifier provides a gain range of 30dB to 60dB. The gain can be controlled with a POT and there is also an external gain port to allow the implementation of automatic gain control.
THe IF Mixer uses an ADE-01 and has the same specifications and features as the RF Mixer.
The RadioLab operates on 12V DC. There is a 1.5A resettable fuse and also includes reverse polarity protection.
Variable Frequency Oscillators
The Si5351 is a silicon-based clock generator IC (integrated circuit) produced by Silicon Labs. It’s a highly versatile device that can generate multiple clock outputs at varying frequencies, making it particularly useful in applications where precise clock signals are required. The Si5351 is often used in radio equipment, especially in amateur radio projects.
Some key features of the Si5351:
Multiple Outputs: It typically has multiple output drivers, with the common variant Si5351A providing 3 independent clock outputs.
Programmable Frequencies: The frequencies of these outputs can be programmed over a wide range, typically from 8 kHz to 160 MHz, which covers most of the needs for digital electronics.
I²C Interface: It is controlled via an I²C serial interface, which allows for easy integration with microcontrollers and processors. Through the I²C interface, the Si5351 can be configured to generate the required frequencies and phase relationships.
Low Jitter: It is designed to produce a low-jitter clock output, which is crucial in many digital communication and signal processing applications where timing precision is vital.
“Poor Man’s” Spectrum Analyser
Combining the Si5351 and an AM detector creates a functional basic spectrum analyzer. Here’s how it works:
Local Oscillator (LO): The Si5351 serves as a tunable local oscillator. You would program it to step through a range of frequencies you are interested in examining.
Filtering: The output of the Si5351 is then passed through a filter or crystal that you’ve designed to only pass the frequency of interest at any given time.
AM Detection: The filtered signal is then sent to an AM detector. The AM detector is a simple diode-based envelope detector that rectifies the signal, followed by a low-pass filter to smooth out the rectified signal and recover the amplitude envelope.
Amplitude Measurement: The output of the AM detector, which corresponds to the strength of the signal at the specific frequency that the Si5351 is currently outputting, is then measured. This is done using an analog-to-digital converter (ADC) in the microcontroller.
Sweeping: By sweeping the Si5351 across the frequency range of interest and taking amplitude measurements at each step, you can build a simple spectrum analyzer. You plot the amplitude of the detected signal against the frequency to visualize the spectrum of the input signal.
This setup does not provide the same level of functionality as a commercial spectrum analyzer, especially in terms of dynamic range, resolution, sensitivity, and the ability to analyze complex signals. However, it can be a useful tool for hobbyist applications or educational purposes to understand the basic principles of spectrum analysis and signal processing.
The RadioLab uses an ESP32 microcontroller board, a 160×128 TFT display, a rotary encoder, and switches, allowing you can create a comprehensive radio receiver / transmitter controller.
ESP32 Microcontroller Board:
160×128 TFT Display:
Push Button Switches:
By integrating these components, you can create a versatile and interactive controller for radio receivers, enhancing the user experience and providing robust control over frequency selection and receiver settings. This setup could serve not only for listening and monitoring but also as an educational tool, demonstrating the intricacies of radio reception, frequency control, and digital signal processing.