In the last 5 years, the availability of powerful DSP and Communications design software, and the emergence of relatively affordable devices that receive and digitize RF signals, has brought Software Defined Radio (SDR) to the desktops of many communications engineers. However, the more recent availability of very low cost SDR devices such as the RTL-SDR, costing less than $20, brings SDR to the home desktop of undergraduate and graduate students, as well as both professional engineers and the maker communities. Since the release of the various open source drivers for the RTL-SDR, many in the digital communications community have used this device to scan the RF spectrum and digitise I/Q signals that are being transmitted in the range 25MHz to 1.75GHz. This wide bandwidth enables the sampling of frequency bands containing signals such as FM radio, ISM signals, GSM, 3G and LTE mobile radio, GPS and so on. In this paper we will describe the opportunity and operation of the RTL-SDR, and the development of a hands-on, open-course for SDR. These educational materials can be integrated into core curriculum undergraduate and graduate courses, and will greatly enhance the teaching of DSP and communications theory, principles and applications. The lab and teaching materials have recently been used in Senior (4th year Undergraduate) courses and are available as open course materials for all to access, use and evolve

We present an unshielded, double-resonance magnetometer in which we have implemented a feedforward measurement scheme in order to suppress periodic magnetic noise arising from, and correlated with, the mains electricity alternating current (AC) line. The technique described here uses a single sensor to track ambient periodic noise and feed forward to suppress it in a subsequent measurement. This feed forward technique has shown significant noise suppression of electrical mains-noise features of up to 22 dB under the fundamental peak at 50 Hz, 3 dB at the first harmonic (100 Hz), and 21 dB at the second harmonic (150 Hz). This technique is software based, requires no additional hardware, and is easy to implement in an existing magnetometer.

We present the design process and implementation of fully open-source, ultra-low noise programmable current source systems in two configurations. Although originally designed as coil drivers for Optically Pumped Magnetometers (OPMs), the device specifications make them potentially useful in a range of applications. The devices feature a bi-directional current range of ±10 and ±250 mA on three independent channels with 16-bit resolution. Both devices feature a narrow 1/f noise bandwidth of 1 Hz, enabling magnetic field manipulation for high-performance OPMs. They exhibit a low noise of 146 pA/[Formula: see text] and 4.1 nA/[Formula: see text], which translates to 15 and 16 ppb/[Formula: see text] noise relative to full scale.

Abstract-Optically pumped atomic magnetometers (OPMs) offer highly sensitive magnetic measurements using compact hardware, offering new possibilities for practical precision sensors. Double-resonance OPM operation is well suited to unshielded magnetometry, due to high sensor dynamic range. However, sensor response is highly anisotropic with variation in the orientation of the magnetic field. We present data quantifying these effects and discuss implications for the design of practical sensors.

Radio communication through attenuating media necessitates the use of very-low frequency (VLF) and ultra-low frequency (ULF) carrier bands, which are frequently used in underwater and underground communication applications. Quantum sensing techniques can be used to circumvent hard constraints on the size, weight and noise floor of classical signal transducers. In this low-frequency range, an optically pumped atomic sample can be used to detect carrier wave modulation resonant with ground-state Zeeman splitting of alkali atoms. Using a compact, self-calibrating system we demonstrate a resonant atomic transducer for digital data encoded using binary phase-and frequency-keying of resonant carrier waves in the 200 Hz -200 kHz range. We present field trial data showing sensor noise floor, decoded data and received bit error rate, and calculate the projected range of sub-sea communication using this device.