sidmon records submarine-transmitter intensities and directions as a means to detect sudden ionospheric disturbances. It captures samples from sound cards from one or two loop antennae, and spectrally analyzes them. It has a spectral-peak measurement algorithm that measures and excludes the background intensity, and also a feature for excluding spectral outliers such as line harmonics. These allow more accurate intensity measurements. A veto feature detects and excludes Fourier frames with excess intensity, which helps exclude noise spikes.

sidmon version 2 was developed in 2017, which is able to measure intensities. sidmon 3 is a more recent developement, able to measure signal directions as well as intensities. When measuring directions, it utilizes two loop loop antennad with orthogonal orientations, and the stereo line/microphone inputs of sound cards with their simultaneous sampling. sidmon 3 is a work in progress, although I am getting good results now with direction sensitivity of ~0.1° with one minute integrations and a strong signal.

sidmon's repository is on sorurceforge.com under the name sidmon3. If down loading using the git clone command, specify the '-b correlate' switch to get the correct branch, and the '--single-branch' switch, e.g.,

git clone -b correlate --single-branch https://git.code.sf.net/p/sidmon3/code sidmon

Documentation is in the doc subdirectory in the files sidmon2.html for the older intensity-only sidmon, sidmon3.html for the direction enhancement, and RaspberryPi.html for setting up an RPi. The last is written in an elementary style fitting my linux level. Most of its content applies to other linux platforms, and I've run sidmon on an x64 computer as well as an RPi.

sidmon is very modest in its cpu usage. On an RPi 4B, it is less than 5% when measuring direction (dual audio channel) as well as intensity. I've tested sidmon with Asus Xonar models U5 and U7 sound cards, the StarTech ICUSBAUDIO2D, and Realtek ALC221 chip in my desktop.