UltraMSK is a software application that runs under the Linux operating system. The software will run on most of the main Linux distribution families e.g. Debian, Ubuntu, RedHat, CentOS, Rocky, Fedora etc. You will need a GPS receiver, a VLF antenna and a computer with a sound card. The computer hardware requirements for UltraMSK are modest and similar to that for running the Linux OS itself. This will depend though upon the number of VLF signals being received. It is also possible to use small single-board computers such as the Raspberry Pi.
Please feel free to contact us should you have any questions about what is needed to get an UltraMSK receiver up and running. A free evaluation of the software is available on request.

UltraMSK system overview

Sound Card

UltraMSK makes use of standard audio sound cards for data acquisition. You will need a sound card with enough input channels to connect each of your VLF antenna signals plus one additional channel to input the GPS 1 PPS signal. Thus for a single vertical electric field antenna, a standard 2 input channel sound card would be OK. For a setup with orthogonal VLF loop antennas, a multichannel card would be required. The sound card must be capable of sampling at either 48 kHz or 96 kHz and must use sigma-delta analog to digital converters.
Many computer motherboards have a built in sound card which may be suitable. PCI cards such as the Creative Audigy SE can be used. Suitable multichannel sound cards include the M-Audio Delta series. USB audio interfaces such as the Focusrite Scarlett range are another option.
UltraMSK uses the VLF Software Receiver Toolkit for data acquisition from the sound card. The Jack Audio Connection Kit or ALSA can also be used.

GPS receiver

A GPS receiver with a precision 1 pulse per second (PPS) output is required. The 1 PPS signal is connected to an input channel of the sound card. The width of the 1 PPS pulse must be either less than or equal to 10 microseconds or else wider than 1 millisecond.
For accurate signal timing, the PC clock must be set to within +/- 500 milliseconds of UTC. This can be achieved using the Network Time Protocol.

VLF antenna

You will need to provide a VLF antenna. You can use electric field whip antennas or magnetic field loop antennas. The signal needs to be preamplified up to a line level suitable for connection to the sound card.