Ionisation is the process in which electrons, which are negatively charged, are removed from (or attached to) neutral atoms or molecules to form positively (or negatively) charged ions and free electrons. It is the ions that give their name to the ionosphere, but it is the much lighter and more freely moving electrons which are important in terms of high frequency (HF: 3 to 30 MHz) radio propagation. Generally, the greater the number of electrons, the higher the frequencies that can be used. During the day there may be four regions present called the D, E, F1 and F2 regions. Their approximate height ranges are:
E region 90 to 140 km;
F1 region 140 to 210 km;
F2 region over 210 km.
Only the E, F1, sporadic E when present, and F2 regions refract HF waves. The D region is important though, because while it does not refract HF radio waves, it does absorb or attenuate them
The lifetime of electrons is greatest in the F2 region which is one reason why it is present at night. Typical lifetimes of electrons in the E, F1 and F2 regions are 20 seconds, 1 minute and 20 minutes, respectively.
Aurora is caused by interaction between the Earth's magnetic field and the solar wind (a mix of charged particles blowing away from the sun). During solar storms, enough of these charged particles make it through to the Earth's upper atmosphere that they interact with the earths natural magnetic field lines. When enough of these particles collide, energy is released in the form of auroral light. In addition to creating a pretty light show (mostly in upper latitudes), radio signals scatter off of these particles and can greatly enhance propagation on 6 meters and above. High levels of aurora can also make propagation via polar routes difficult. This plot shows 3-days of 5-minute solar x-ray flux values measured on the SWPC primary and secondary GOES satellites. One low value may appear prior to eclipse periods. Click on the plot to open an updating secondary window This images dynamically updates once a minute. specialy designed by NOAA National Weather and Space Service Prediction Center. for HF Radio communications prediction. Click on any thumbnail to view a larger image. Real-Time Northern Hemisphere Auroral Activity Real-Time Southern Hemisphere Auroral Activity
Solar X-ray Flux D-Region Absorption Prediction Map
Artical taken from
Issued by Pascal
These day's Amateur Radio is not only for talking thru a microphone anymore. No Sir, Various modes of communication are available to ham operators.
One such mode of much interest is the Digital mode.
Which Digital mode you ask?,
Well, there again you have a variety of selections and groups involved.
Here is an attempt to explain how simple it is to tune and decode this exciting digital broadcasts and how one can get involved even without having an amateur license. All you need is a radio connected with a computer and some software.
The digital side of amateur radio allows data to be sent over the airwaves.
With your computer, your radio, and appropriate cables, you can hook the two together and communicate to others - No other special hardware necessary, although if desired, it can be optional. There are a number of digital modes that grace the airwaves these days. Some of the modes are intended for the lower HF bands, where communication can be made over longer distances.
Others are intended for local areas, using VHF and/or UHF frequencies, but can be extended over longer distances using digital repeaters, or digipeaters. Some of the digital modes can be done with just your computer and radio - using the computer's sound card to receive and decode the bits of information from audio to data.
All that is needed to use sound card modes is audio cables between your radio and sound card, and a cable hooking up to either the serial or parallel port on your computer to handle the PTT on the radio. You can use plain old cables, or there are a number of companies that make interfaces to simplify hookup - Hook common cables to an interface box, and plug the box into your radio. Some of the interfaces will reduce the audio output a small amount, allowing a clean audio signal to go between the radio and the computer, and vice versa.
Overview Digital Radio Operating Modes:
Article taken from
This plot shows 3-days of 5-minute solar x-ray flux values measured on the SWPC primary and secondary GOES satellites. One low value may appear prior to eclipse periods. Click on the plot to open an updating secondary window
This images dynamically updates once a minute. specialy designed by NOAA National Weather and Space Service Prediction Center. for HF Radio communications prediction. Click on any thumbnail to view a larger image.
Real-Time Northern Hemisphere Auroral Activity Real-Time Southern Hemisphere Auroral Activity
Real-Time Southern Hemisphere Auroral Activity