SID stands for Sudden Ionosphere Disturbance, which are usually caused by solar flares. Members of the American Association of Variable Star Observers (AAVSO) SID program use inexpensive radio equipment to detect and record these quick changes of the ionosphere. Members then send in reports at the end of the month listing SIDs they have recorded. Their reports typically contain the time a SID starts, peaks, and ends. The ability to detect solar flares with radio immediately caught our attention. The theory behind the program is not difficult to understand. But constructing the equipment for the SID monitoring station was a little over our head. So it appeared best to drop the idea. Then it became apparent that a SID monitoring station could be constructed with the help of NJAA research members. Also the station could be located at the observatory and be used by members wishing to get a taste of amateur research.
High Frequency (HF) radio waves and Very Long Frequency (VLF) radio waves typically bounce off the ionosphere and the earth. Hence these radio signals can literally travel great distances by bouncing from the earth to the ionosphere many times. In brief, a VLF or HF signal transmitted in Europe can be received without difficulty in America. (Note* Typical FM radio signals do not use the ionosphere in such a way, hence we do not hear FM radio stations from very distant transmitters). Many countries, including the U.S., use VLF signals to communicate with their submarines. This is due to the VLF signals excellent ability to travel the earth. Our receiver will most likely use NAA, a US Naval VLF radio station in Maine. NAA is located at 24.0 kHz and puts out a continuous signal.