For our latitude (nort-west of Italy) we have decided to use Cyprus 2 wich has an intervall time of 300″ and a offset time of 240″.
You will need to calculate the great circle distance between your location and cyprus (or any other ionosonde). For this project we have used three main piece of hardware : The units are connected in this way : The GPS unit output (10MHz and 1PPS are connected to the USRP2 ext clock input Ref.
Both vertical and oblique sounding work on the same basic principles and the main difference between these two techniques is the location of the transmitter with respect to the receiver, in this case we are using an Oblique ionogram.
Obliquely propagating waves are gradually refracted as they travel trough an ionospheric layer with increasing electron density, making them more receptive for variations in the ionosphere.
In this spectrogram as an example, the frequencies between 19-24MHz using a single reflection from the ionosphere would be available to a HF radio user to establish communications between Svalbard and Chilton.
Between 13 to 15MHz would also available utilising a propagation route that involves two reflections from the ionosphere and one reflection from the ground.
The different ionization layers or regions influence radio waves propagation depending on elctron density of free electrons.
Two types of ionosonde exist, Vertical and Oblique.
Solar flares are associated with release of charged particles into the solar wind that reaches the Earth and interacts with the geomagnetic field.
In principle between 7-11MHz would also be available using either two, three and four ionospheric reflection propagation.