UltraMSK block diagram

UltraMSK is a software application that runs under the Linux operating system. The CentOS distribution of Linux is recommended. 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 CentOS. This will depend though upon the number of VLF signals being received. For example, an AMD Semperon 2500+ CPU will use around 10 % of its CPU processing time to receive 6 VLF signals.

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.

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. More information on Linux sound card drivers can be found at the ALSA project.

UltraMSK uses the Jack Audio Connection Kit or ALSA for data acquisition from the sound card.

GPS receiver

A GPS receiver with a precision 1 pulse per second (PPS) ouput 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.