Signals from the Subatomic World: How to Build a Proton Precession Magnetometer - cover image

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Signals from the Subatomic World: How to Build a Proton Precession Magnetometer

Stefan Hollos and J. Richard Hollos

Format and pricing: Paperback (150 pages) $24.95, Kindle/pdf $9.95
ISBN: 9781887187008 (paperback), 9781887187091 (ebook)
Publication date: May 2008

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This book is also available in paperback at most bookstores and distributors, including these:

Table of Contents

    1  Introduction
        1.1  The proton precession magnetometer
        1.2  How PPM’s work
        1.3  Overview of magnetometer

    2  Polarization Coil and Platform
        2.1  Materials not allowed
        2.2  Wire for polarizing coil
        2.3  Purpose of polarizing coil
        2.4  Positioning polarizing coil
        2.5  Inductance of a coil
        2.6  Magnetic field strength due to coil
        2.7  Polarizing coil parts list
        2.8  Specifications of polarizing coil
        2.9  Construction of polarizing coil
        2.10  Tiltable platform parts list
        2.11  Construction of tiltable platform

    3  Pulse Controller
        3.1  Purpose of pulse controller
        3.2  Quenching the current
        3.3  How a MOSFET works
        3.4  Advantage of using multiple MOSFETs
        3.5  Pulse controller circuit description
        3.6  Microcontroller circuit description
        3.7  Microcontroller software
        3.8  Power supply
        3.9  Assembly and enclosure
        3.10  Pulse controller parts list

    4  Sensor Coil
        4.1  Sensor coil requirements
        4.2  How the coils are wired together
        4.3  How to connect cable to coils
        4.4  Specifications of sensor coil
        4.5  Sensor coils parts list
        4.6  Construction of sensor coils

The content below here is only available with the book.

    5  Amplifier
        5.1  Why a differential amplifier is best
        5.2  Why a low noise amplifier is needed
        5.3  Description of amplifier circuit
        5.4  Supplying power to the amplifier
        5.5  Layout of amplifier circuit
        5.6  Capacitors at amplifier input
        5.7  Estimating precession frequency
        5.8  Amplifier parts list

    6  Data Acquisition and PC Control
        6.1  What sampling rate to use
        6.2  What resolution to use
        6.3  How long to take data
        6.4  The ADC board used in the Magnum
        6.5  Pulse controller and data acquisition software

    7  Data Processing and Analysis
        7.1  Signal averaging
            7.1.1  Why it improves signal to noise ratio
            7.1.2  Limits due to MOSFET slow down
        7.2  Filtering the data
        7.3  Spectral analysis using the FFT
        7.4  Converting bin number to actual frequency
        7.5  High resolution spectrum for peak location

    A  Magnum Control Program

    B  Microcontroller Program



This book is an excellent introduction to proton precession magnetometers. It starts with a simple nontechnical explanation of how these magnetometers work. The rest of the book is then devoted to a detailed description of how to build a magnetometer called the Magnum. The table of contents and sample chapters can be found below. The software for this book can also be found below.

About the authors

Stefan Hollos and J. Richard Hollos are physicists and electrical engineers by training, and enjoy anything related to math, physics, engineering and computing. They are brothers and business partners at Exstrom Laboratories LLC in Longmont, Colorado.

Software for the book:

  1. - contains the software for operating the Magnum:
    • mc.c - manual control program for the Magnum pulse controller.
    • adl.c - the program that handles the overall control and operation of the Magnum.
    • mag4.asm - allows the AT90S2313 microcontroller to receive instructions from a PC running the ADL program and then execute those instructions.
  2. - contains all gerber files and instructions needed for ordering the printed circuit boards from a manufacturer. The manufacturer we have used is Advanced Circuits at
  3. magnum1.pcb - printed circuit board file for use with the PCB program. This program is freely available at

Proton Precession Frequency Calculator

Converts from nanoTesla to frequency or vice versa.
Click an arrow button to convert.

NanoTesla: Freq. [Hz]:

Send comments to: Richard Hollos (richard[AT]exstrom DOT com)
Copyright 2020 by Exstrom Laboratories LLC