The
Radio Lab
for builders

All the building blocks to experiment and build radios

  • AM, SSB and FM
  • LW to VHF
  • 0 – 2GHZ RF Amplifier
  • 0 – 500MHz Mixers
  • Variable Gain 60dB IF amplifier
  • 7 Watt Audio Amplifier
  • 3 Signal Generators 8KHz to 160MHz
  • Color Display
  • ESP32 Controller
  • RF and IF Filter
  • 3 Prototyping areas
  • Spectrum Analyzer Detector
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What is the RadioLab

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. 

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Projects you can build

Direct Conversion Receiver

The Direct Conversion receiver works as follows:

  1. The RF signal from the antenna goes through the 40M bandpass filter to reject out-of-band signals.
  2. The filtered RF signal is then fed into the ADE-1 mixer.
  3. Simultaneously, the Si5351 under the control of the ESP32 generates a variable frequency LO signal that matches the frequency of the desired RF signal.
  4. The ADE-1 mixer mixes the RF signal with the LO signal, resulting in the audio frequency signal corresponding to the original RF signal’s modulation.
  5. The audio signal from the mixer is then passed to the TDA7266M amplifier to drive the output device (speaker or headphones).
  6. The ESP32 controls the display to provide a user interface and responds to user input via the encoder and switches to adjust frequency, volume, and other settings.

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.

Superheterodyne Receiver

The following changes or additional components required for the superheterodyne architecture:

  1. Additional Mixer and Local Oscillator:

    • An extra mixer is used to convert the IF signal to audio frequency, requiring an additional LO signal, which could be the second output from the Si5351.

  2. Intermediate Frequency (IF) Stage:

    • Includes an IF filter (like a crystal filter), which is not present in the direct conversion receiver, to select the desired IF signal with high selectivity.

  3. Fixed-Frequency Local Oscillator for IF:

    • A second fixed-frequency LO is introduced to mix with the first IF signal, producing a consistent second IF where most of the signal processing is done. This frequency is not changed during tuning.

  4. Variable IF Amplifier:

    • An amplifier designed specifically for the IF stage with variable gain, which may incorporate automatic gain control (AGC).

  5. IF Selectivity:

    • The crystal filter centered at the IF frequency provides better selectivity than the simpler filters used in direct conversion receivers.

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.

Spectrum Analyser

Combining the Si5351 and an AM detector creates a functional  basic spectrum analyzer.

This tool can be used for the following:

  • RF Bandpass Filters
  • Crystal selection for IF Filters
  • IF Filter shape and bandwidth

 

Frequency Counter

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.

Slow Scan TV

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:

  1. High Gain Op-Amp:

    • The SSTV signal, which is an audio signal, is first amplified by a high gain op-amp.
    • The amplified signal is then fed into a Schmitt trigger.

  2. Interrupt on Rising Edge:

    • The digital output  is connected to an interrupt pin on the microcontroller. The microcontroller is configured to trigger an interrupt service routine (ISR) on the rising edge of this digital signal.

  3. Frequency Measurement via Time Elapsed Between Interrupts:

    • To decode the SSTV signal, you need to measure the frequency of the audio tones. Since the frequency of a wave is inversely proportional to the period (the time between successive waves), you can measure the frequency by timing the period between the rising edges.
    • When an interrupt occurs, it indicates the start of a new period. By recording the time when the previous interrupt occurred, you can calculate the time elapsed between interrupts, which is the period of the audio tone.
    • Once you know the period, you can calculate the frequency by taking the inverse of the period (Frequency = 1 / Period).

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.

Prototyping Area

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.

LM386 Audio Amplifier

SSTV Decoder Circuit

RF Bandpass Filter

Plug In Modules

Software Defined Radio

The SDR (Software Defined Radio) module processes the RF signals to audio output. The signal flow from antenna to speaker is as follows.

  1. Antenna and Bandpass Filter (BPF):

    • The RF signal is received by the antenna and then passed through a bandpass filter which selects the desired frequency band, attenuating frequencies outside this range to reduce noise and interference.

  2. Local Oscillator and Mixer:

    • The Si5351 generates two quadrature local oscillator signals (0° and 90° phase shift) which are fed into the SN74CBT3253DR IC, acting as a double balanced mixer.
    • The mixer down-converts the RF signals to baseband I (In-phase) and Q (Quadrature-phase) signals.

  3. Amplification and Filtering:

    • The I and Q signals are then amplified by two sections of NE5532ADR op-amps to ensure they are at the correct level for the ADC.
    • The CS5343-CZZ ADC converts the analog I and Q signals into digital I2S format.

  4. Digital Signal Processing (ESP32):

    • The ESP32 processes the digital I2S signals, performing Hilbert transform filtering to select the desired mode, such as SSB with a 3 kHz lowpass filter or CW with an 800 Hz bandpass filter. This digital processing effectively isolates the signals within the desired frequency range for listening.

  5. Digital to Analog Conversion:

    • The filtered digital I2S signals are then sent to a CS4344-CZZ DAC which converts them back into analog form.

  6. Summation and Output:

    • The filtered analog I and Q signals are then summed using another stage of NE5532ADR op-amp. This summing process combines the signals into a single audio signal.
    • The summed audio signal is then sent to an audio amplifier (not shown in detail) and finally to a speaker, where the listener can hear the decoded signal.

 

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.

Transmitter Module

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:

  1. Si5351 Clock Generator:

    • This device generates the RF carrier frequency for the transmitter. It is controlled by the ESP32, which sets the desired transmit frequency within the 40M amateur radio band or potentially other bands, depending on the plug-in filters.

  2. 40M RF Bandpass Filter:

    • This filter is designed to pass signals in the 40-meter band (7.0 – 7.3 MHz) while attenuating frequencies outside this range. It ensures that the transmitted signal is clean and within the allocated amateur radio band.

  3. Optional Plug-In Filter:

    • The module allows for an optional filter to be plugged in, which could be designed for different bands. This makes the transmitter versatile and capable of operating on multiple amateur bands.

  4. 50 Ohm Dummy Load:

    • For testing purposes, a 50 Ohm dummy load can be used. This allows you to test the transmitter without radiating a signal, which is useful for setup and troubleshooting without interfering with other communications or violating regulations.

  5. Transistor Amplifier:

    • The schematic shows a BS170 MOSFET, which is part of the transmitter’s power amplifier. This amplifies the RF signal from the Si5351 to a level suitable for transmission.

  6. Digital I/O Interface:

    • The ESP32 interfaces with the transmitter module via digital I/O lines, which  controls the transmit/receive switching, activate the transmitter, and handle other signaling required for operation.

Universal Radio Module

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:

  1. 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.

  2. 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.

  3. Automatic Frequency Control (AFC): AFC helps in keeping the receiver tuned accurately to the desired station, reducing drift caused by factors like temperature variations.

  4. 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.

  5. 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.

  6. SPI/I2C Control: The IC can be controlled and configured using standard serial communication interface I2C (Inter-Integrated Circuit).

  7. Analog Audio Output: It provides analog audio output for connecting to speakers or headphones.

  8. Programmable Features: It offers various programmable features and settings to customize the radio receiver’s behavior to suit different applications and regions.

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RadioLab - Individual hardware blocks

RF Filter
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.

RF Mixer
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:

  1. Function: The ADE-01 is an RF double-balanced mixer. Like other RF mixers, it is designed for frequency conversion, allowing you to translate RF signals from one frequency to another.
  2. Frequency Range: The ADE-01 operates from 0.5MHz to 500MHz making it useable up to the VHF / UHF frerquencies.
  3. Double-Balanced Design: This mixer incorporates a double-balanced design, which provides good port-to-port isolation and helps minimize unwanted harmonics in the output signal.
  4. Low Conversion Loss: It is designed for low conversion loss ( 5dB Typical ) to minimize signal power loss during the mixing process, making it suitable for applications where signal integrity is critical.
  5. Port Isolation: The ADE-01 typically features port isolation of 55dB

RF Amplifier
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.

  1. Low Noise Figure: The amplifier is designed with low noise figure 3.8dB, making it suitable for sensitive RF receivers. Low noise is crucial for maintaining signal quality in communication systems.
  2. High Gain: 25dB of gain across a wide frequency band, which is beneficial for amplifying weak signals or for compensating for signal losses in RF systems.
  3. Consistent Performance: MMICs are manufactured using standardized semiconductor processes, ensuring consistent performance and repeatability from one IC to another. This predictability simplifies the design and production process.
  4. Broadband Matching: The BGA2815 include on-chip matching networks, which are designed for optimal performance over the specified frequency range. This eliminates the need for external matching components and simplifies circuit design.

Crystal Filter
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.

  1. Filter Configuration: The SSB crystal ladder filter consists of four matched crystals in a ladder-like arrangement. These crystal resonators are piezoelectric devices that have a precise and stable resonant frequency 9.21MHz determined by their physical dimensions and crystal properties.
  2.  Low Loss: Crystal ladder filters are known for their low insertion loss, meaning they don’t significantly attenuate the desired signal when it passes through the filter. This is important to maintain signal quality.
  3. Impedance Matching: The input and output of the filter are impedance-matched to 50 Ohms matching the surrounding RF circuitry to minimize reflections and ensure efficient signal transfer.
    Application: SSB crystal ladder filters are commonly used in SSB transceivers, HF (High Frequency) radios, and other communication systems where bandwidth efficiency and precise frequency selectivity are crucial. They help to improve signal quality and reduce interference.

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.

IF Mixer
THe IF Mixer uses an ADE-01 and has the same specifications and features as the RF Mixer.

Power In

The RadioLab operates on 12V DC. There is a 1.5A resettable fuse and also includes reverse polarity protection.

Audio Amplifier

  1. The audio amplifier has an LC low pass filter to reduce high frequency hiss.
  2. There is a preamplifier with a selectable 50 Ohm termination.
  3. The preamplifier can be bypassed with a direct input to the power amplifier.
  4. The power amplifier is the TDA7266M, which is a mono bridge amplifier specially designed for TV and Portable Radio applications.
  5. 7 watts of output is available giving enough volume to fill a room.
  6. The audio power amplifier has thermal overload and short circuit protection built in.
  7. An external mute port is made available for transceiver applications.

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:

  1. Multiple Outputs: It typically has multiple output drivers, with the common variant Si5351A providing 3 independent clock outputs.

  2. 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.

  3. 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.

  4. 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:

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

Microcontroller Section

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:

  1. Frequency Tuning: Utilize the ESP32 to control the Si5351 clock generator, providing precise frequency tuning for the radio receiver.
  2. Signal Processing: Implement software-defined radio (SDR) techniques to process incoming RF signals. The ESP32 can handle demodulation of signals (AM, FM, SSB, CW, etc.), depending on the complexity and the receiver’s architecture.
  3. User Interface: Manage the interface displayed on the TFT, reading the encoder input, and debouncing the switches for stable operation.
  4. Connectivity: Take advantage of the Wi-Fi/Bluetooth capability for remote control or additional functionalities like streaming audio or updating receiver firmware.

160×128 TFT Display:

  1. Frequency Display: Show the current frequency to which the receiver is tuned.
  2. Spectrum Visualization: When used with a software-defined radio approach, it could show a real-time band scope or waterfall display.
  3. Receiver Status: Indicate the mode of operation (AM, FM, SSB, etc.), signal strength (S-meter), and other receiver statuses like volume level.

Rotary Encoder:

  1. Fine Tuning: Allow fine-tuning of the receiver frequency. The increment/decrement step size could be adjusted for quick scanning or precise tuning.
  2. Menu Navigation: Navigate through menus for additional settings and receiver options.

Push Button Switches:

  1. Mode Selection: Change the modulation mode of the receiver (e.g., AM, FM, LSB, USB).
  2. Band Selection: Quickly switch between predefined frequency bands or channels.
  3. Filter Selection: Choose among different bandwidth filters for signal optimization.
  4. Mute or Volume Control: Mute the audio output or adjust the volume.

Frequency Control:

  1. Direct Frequency Entry: With a combination of switches and encoder, implement a direct frequency entry system, allowing users to quickly jump to specific frequencies.
  2. Memory Channels: Use the ESP32’s memory to store favorite frequencies or channels for quick access.
  3. Scan Function: Implement a scanning function to automatically search for active frequencies within certain bands.
  4. Automatic Gain Control (AGC): Control the AGC settings for optimal listening experience across different signal strengths.

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.

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