STEMlab RED PITAYA SDR Transceiver Build Part 4

 

In the last instalment (Part 3) of my STEMlab Red Pitaya SDR transceiver project, I covered the process of moving some of the control logic off the Red Pitaya and onto the controller module I designed around an STM32 “Blue Pill” microcontroller. This shift has given me far more reliable handling of RX/TX transitions, cleaner timing, and full control over the PE4302 attenuation stages—something the SDR software alone couldn’t provide. The effort that went into designing the controller and writing the firmware is now paying dividends, as the module has become the central piece that ties the hardware together and keeps the system predictable while I continue developing the rest of the transceiver. With the receive path behaving exactly as intended, the controller is now ready to support the next phase of the build as I move toward completing the transmit chain and integrating PureSignal.

As the build progresses, I’m really starting to appreciate the benefits of the new features being added. The digital attenuator in the receive path has already proven its worth, especially when strong nearby signals or a barrage of contest stations threaten to overload the ADC. Automatic switching of the RF preamplifier on the higher bands has also become a welcome addition, bringing weaker signals up out of the noise without me having to remember to enable it manually. These refinements make the receive chain far more robust and user‑friendly as the project continues to evolve.

In this blog post, I explore the role of audio codecs in my transceiver build, specifically how they convert analogue microphone signals into digital data for transmission, and then back into analogue audio for clean, low latency monitoring and listening. This marks an important step toward completing the audio path and integrating full voice capability into the SDR architecture.

STEMlab RED PITAYA SDR Transceiver Build Part 3

 

In the last instalment of my Stemlab Red Pitaya SDR transceiver project, I completed the design and build of the receiver front‑end module, which includes an RF pre‑amp, bandpass filters, and a digital attenuator. This module improves the Red Pitaya’s receiving performance and adds an extra layer of protection to the Pitaya’s ADC input.

With the new receiver front‑end built and tested, I’ve thoroughly enjoyed listening to the HF bands and evaluating the enhanced performance of the Red Pitaya when integrated with the superb Thetis software.

If you are not familiar with the Thetis software, it is an advanced SDR client originally developed for the Apache Labs ANAN transceivers, and it’s become a popular choice for Red Pitaya‑based SDR projects. It provides a highly configurable interface, low‑latency DSP, powerful filtering, and excellent visualization tools. With features like adaptive noise reduction, customizable panadapter displays, and flexible transmit/receive profiles, Thetis brings out the full potential of the Red Pitaya hardware and offers a polished, professional operating experience.

To continue documenting my SDR transceiver build, this post covers the design and construction of a dedicated controller that enhances and complements the Red Pitaya module, the heart of the project.

STEMlab RED PITAYA SDR Transceiver Build Part 2

Now that the Stemlab Red Pitaya 125-14 module has been modified for use as an SDR (software defined radio), it is time to design and build a front end module with filtering, RF amplification and digital attenuation.

The Red Pitaya board has very wideband, high-speed ADC's that will digitize everything from DC up to tens of MHz and while this is desirable for a software-defined radio receiver, it is not without some downsides.

Building an SDR transceiver with the STEMlab Red Pitaya.

 

The Red Pitaya board itself is a compact, open‑source FPGA‑based test and measurement platform. It’s often described as a Swiss‑army knife for electronics because it can act as an oscilloscope, signal generator, spectrum analyzer, VNA, logic analyzer, and more. It is fully open-source and widely used in industry, education, RF labs and hobbyist electronics.

HF Transceiver VFO Microcontroller Software.

In this blog post, I present an overview of the "Irwell HF Transceivers" vfo microcontroller software. It is intended as a guide to key features for those who have requested the software or are building the transceiver. 

The software and MCU hardware are responsible for generating the VFO signal, oscillator frequencies and to provide control of the various transceiver stages.

The main VFO and controller hardware is based around an affordable STM32 Bluepill microcontroller board.

A High Performance HF Transceiver RF Subsystem.

 

In this blog post I bring some of the completed "Irwell HF Transceiver" modules together and consolidate them on to a single PCB.

Modifying An Analogue Meter.

In this blog post, I go all OLD SCHOOL and prepare an analogues s-meter for my  Irwell HF Transceiver project. 

Big thanks to my ham radio buddy Frank G6YAQ who kindly donated the meter for this project.

Irwell HF Transceiver Digital Modes Interface

 

My last blog post was made on the 10th July 2022, which is just a tad over four and a half months ago. Traditionaly, I do not spend a lot of time during the summer months working on homebrew projects but now that autumn & winter are here, it is time to melt some solder again and play catch up!

Irwell HF Transceiver VFO Oscillator Module Re-Visited Pt2

For part 1 of revisiting the Digital VFO Oscillator  module click here.

 

In the last blog post, I looked at replacing the three 25MHz xtals that are used for  reference clocks on the Si5351 ICs located in the the oscillator module of my digital VFO. 

The mod/upgrade to a single TCXO (temperature controlled xtal oscillator) module was carried out and tested in a lash-up fashion with great success. In this blog post, I report on the fabrication of a new PCB that is TCXO ready!

Irwell HF Transceiver VFO Oscillator Module Re-Visited Pt1

 

My last blog post was in February of this year (2022) and it is hard to believe we are now at the end of the month of May and close to the halfway point of 2022!

I expect followers of the blog may have been left wondering if my Irwell HF Transceiver project has been abandoned but alas that is definitely not the case!

Balanced Modulator For The Irwell HF Transceiver

Before I get into the first blog post for 2022, I would like to take the opportunity to wish everyone who follows the blog a belated happy new year.

HF Transceiver - Modulator

"High Performance AM, CW & SSB Modulator for the G6LBQ Irwell HF Transceiver"

In this blog post, I cover work on the first of the transmitter modules for my Irwell HF Transceiver, a multi-mode modulator that is capable of SSB, AM and CW modes.

The Cascode IF Amplifier Revisited

 For my original Cascode IF Amplifier article click here.

Cascode IF Amplifier Updates

"For The G6LBQ Irwell HF Transceiver"

Welcome to my blog post on the Cascode IF amplifier where, I address a problem that I discovered with the AM demodulator circuit and I also update the PCB to include the S-Meter electronics.

A note to self for future reference: 

"pay closer attention to manufacturers' product data sheets"

Part 5 Of A Digital VFO For The G6LBQ Irwell HF Transceiver

For part 1 of the Digital VFO click here.

For part 2 of the Digital VFO click here.

For part 3 of the Digital VFO click here.

For part 4 of the Digital VFO click here.

Digital VFO I/O Expander Module

"For The G6LBQ Irwell HF Transceiver"

Welcome to part 5 of my blog post series covering the Digital VFO developed for use with my “Irwell HF Transceiver project”.

In this concluding article, I present the I/O expander module, which interfaces to the STM32 microcontrollers I2C bus, its job is to extend the number of digital outputs available and provide switched logic outputs to drive my BPF and LPF transceiver modules.

Illustration of the I/O expander

 

 

 

Band Pass Filtering For The G6LBQ Irwell HF Transceiver Part 3

 For part 1 of the BPF module click here.

For part 2 of the BPF module click here.

HF Transceiver - Band Pass Filter Module

"High Performance RF Band Pass Filtering For The G6LBQ Irwell HF Transceiver"

In this blog post, I conclude the development of my high performance RF Band-Pass Filter suitable for the Irwell HF Transceiver as well as SDR receivers and other transceiver builds.

Band Pass Filtering For The G6LBQ Irwell HF Transceiver Part 2

For part 1 of the BandPass Filter click here.

HF Transceiver - Band Pass Filter Module

"High Performance RF Band Pass Filtering for the G6LBQ Irwell HF Transceiver"

Band Pass Filtering For The G6LBQ Irwell HF Transceiver Part 1

 

HF Transceiver - Band-Pass Filter Module

"High Performance RF Band Pass Filtering for the G6LBQ Irwell HF Transceiver"

In this blog post, I lay the foundations for a high-performance RF Band Pass Filter  suitable for the Irwell HF Transceiver as well as SDR receivers and other transceiver builds.

For my own transceiver project, the filter module needs to meet the following criteria:

• Have a sufficient number of filters to enable general coverage reception of 0.5MHz to 30MHz and provide uniform high performance for any given frequency within this range.
  
  
• Be usable on the transmit path with a rf power handling rated at 1 watt.
  
  
• Provide good suppression to frequencies that fall below or above the desired frequency pass band.
  
  
• Provide low insertion loss within the wanted pass band & good return loss.
  
  

Part 4 Of A Digital VFO For The G6LBQ Irwell HF Transceiver

For part 1 of the Digital VFO click here.

For part 2 of the Digital VFO click here.

For part 3 of the Digital VFO click here.

Digital VFO & RF Oscillator Module

"For the G6LBQ Irwell HF Transceiver"

Welcome to part 4 of my blog post series detailing the Digital VFO and RF oscillator module for my “Irwell HF Transceiver" project.  

The PCBs have arrived from the fabrication plant so it is now time to get busy with the soldering iron and hopefully call time on this part of the project, or at least for now. Providing there are no issues with the PCBs or hardware, all that remains to be done is software updates to coincide with the future development of the project.

A trio of G6LBQ VFO boards.

Part 3 Of A Digital VFO For The G6LBQ Irwell HF Transceiver

For part 1 of the Digital VFO click here.

For part 2 of the Digital VFO click here.

Digital VFO & RF Oscillator Module

"For the G6LBQ Irwell HF Transceiver"

Welcome to part 3 of my blog post series in which I present details of the hardware for my Digital VFO and RF oscillator module. This is a significant building block for the “Irwell HF Transceiver" project and I Present my buffer amplifiers for the SI5351 ICs and design a PCB to produce a completed working module.

My prototype SI5351 buffer & signal splitter circuit!

 

 

Part 2 Of A Digital VFO For The G6LBQ Irwell HF Transceiver

For part 1 of the Digital VFO click here.

Digital VFO & RF Oscillator Module

"For The G6LBQ Irwell HF Transceiver"

Welcome to part 2 of my blog post series in which I present further details of my Digital VFO and RF oscillator module for the “Irwell HF Transceiver" project. This is a significant building block and is solely responsible for frequency generation and the control of other modules in the project.

Since I posted part 1 on the blog, I have made good progress with the software changes that I outlined. I have added additional commands to JA2GQP’s source code for the I2C Multiplexer and I am now at the stage where I can communicate with two SI5351 devices to produce two chip independent clock signals. In order to achieve this, I have had to make changes to both the main code as well as the SI5351 library file.

For now, I only need to generate two clock signals for my transceiver, one for the VFO and the other for the BFO. This will permit the radio to run as a single conversion superhet in its current state. Once further modules are developed, the receiver will be upgraded to a dual conversion superhet, this will require a third clock signal  for the requisite conversion oscillator.

The additional software code required to support a third SI5351 is going to be a bit more difficult for me to implement. I hope to replicate JA2GQP’s BFO oscillator code for this as it includes a routine for calibrating the BFO frequency and saving it to memory. If I can do this, it should also pave the way for implementing an IF shift control.

Part 1 Of A Digital VFO For The G6LBQ Irwell HF Transceiver

 Digital VFO & RF Oscillator Module

"For the G6LBQ Irwell HF Transceiver"

In this blog post, I present my digital VFO and RF Oscillator module for the Irwell HF Transceiver project, which is based on the Silicon Labs CMOS SI5351 Clock Generator.

Before we begin, I would like to pay homage to an era in my life which has flourished and brought great happiness, prosperity and achievement. 

I make the aforementioned statement with a sense of humbleness and I also feel privileged to have experienced great wealth in the recent flourishing times. 

If all this has got you thinking, I have won the national lottery or been a beneficiary to a nice windfall you are excused and forgiven :)  The truth is I have only ever been good at making other people wealthy and said people choose to forget what the catalyst was for their wealth status. Those people know who they are, shame on you!

I digress a little as I sailed off course for a moment there but suffice to say I am very happy with my modest lifestyle.