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Spectrum Analyser | Telephone Exchange | FORTH Computers | VB Profiler | Wireless Thermostat | Ethernet Receiver | Frequency Synthesizers | Core Memory | Spread Spectrum | Avalanche Pulse Generator | Delta Loop Antenna | Huff & Puff | Duplex Radio-Telephone | GPS Receiver | GPU_FFT

Spectrum Analyser

This DC to 50 MHz spectrum analyser uses a standard oscilloscope for display. Dynamic range is better than 70dB using the received signal strength indicator (RSSI) of an FM demodulator IC.

Telephone Exchange

This miniature, 8-line home telephone exchange (PABX) works with standard telephones and features high-quality, user-friendly progress tones and AC ringing. The exchange is all solid-state: no relays.

Mark 1 FORTH Computer

A microcoded stack computer built from discrete logic.

Mark 2 FORTH Computer

Here's another, this time using bitslice and programmable logic devices.

What is FORTH?

Visual Basic Profiler

Here's a software project. This profiler will help you optimise the performance of middle-tier Visual Basic DLLs running under ASP, Microsoft Transaction Server (MTS) on NT4 and Component Services (COM+) on Windows 2000. You can also profile VB Form executables.

Wireless Thermostat

Over the mains carrier current remote control for central heating. Unusually for me, this project was mounted in a box!

Ethernet Receiver

Capturing 10BASE-T Ethernet packets using PLL clock recovery.
Left: a capture transient on the VCO control line.

Fractional-N frequency synthesizers

38-76 MHz and 800-1600 MHz fractional-N synthesizers using Spartan 3 FPGA
15-25 MHz fractional-N synthesizer with 1 Hz steps
Fast & accurate behavioral PLL simulator
Reducing PWM distortion phase noise in fractional-N synthesizers (PDF)
My first fractional-N frequency synthesizer
RACAL RA1792 synthesizer.   Dana Digiphase synthesizer.

Magnetic Core Memory

An experiment to observe the sense output whilst flipping the state of a single bit in an early Univac III magnetic core memory plane.

Spread Spectrum Link

Experimental direct sequence spread spectrum (DSSS) voice link.

Avalanche Pulse Generator

500 pico-second rise and fall time with one transistor!

Delta Loop Antenna

A water-resistant back-garden HF receiving loop for general shortwave listening.

Huff & Puff VFO Stabiliser

A "fast" Huff & Puff VFO stabiliser using a CPLD.

A Portable Duplex Radio-Telephone (PDF)
Lewis and Milner; THE WIRELESS ENGINEER; September, 1936.

"A practical system of duplex radio-telephony [...] in which each set is made alternately transmitter and receiver at a supersonic frequency. The interrupted oscillation provides super-regenerative amplification [...] The quench frequency must be selected according to the distance between the sets."

Duplex Radio-Telephone (Revisited)

Re-creating Lewis and Milner's 1930's experiments with modern (well, 1970's) components. They used just two valves! This design employs four 4000-series CMOS ICs and a dual-gate MOSFET to achieve full-duplex telephony with phase-locked quench oscillators.

Homemade GPS Receiver

A homemade GPS receiver built from the ground up using discrete components and featuring a limiting IF followed by 1-bit ADC ahead of DSP signal processing in a Xilinx Spartan 3 FPGA. Fast FFT-based search, and navigational solutions computed by "C" code on Windows and Linux. May 2013: 12-channel, battery-powered, truly-portable Raspberry Pi version. September 2014: Source re-released under GNU GPL.


An FFT library for the Raspberry Pi which exploits the BCM2835 GPU V3D hardware to deliver ten times more data throughput than is possible on the 700 MHz ARM.