Alex Discovers Amateur Radio

8 # 2 The strength of ionisation in the ionosphere depends on the amount of radiation, mainly UV , received from the sun. It varies with the time of day, and with the season, i.e. summer to winter, and with other factors such as sun spots and electromagnetic storms. The stronger the level of ionisation the higher the frequency of signals that will be bent (refracted) back. VHF and UHF signals usually pass straight through into space. During the day signals as high as 30MHz can be bent back - at night this is lower, often 3MHz or less. The highest frequency refracted back at a particular time is called the M aximum U sable F requency for long distance contacts - MUF . Amateur Radio is fun! Watch! G1PSK . This is M6CAM M6CAM This is G1PSK . How’s it going, dad? Okay, see you then M6CAM , out. Great! I just made contact with France on 40 metres and Canada on 20 metres. Meet me for lunch at 13 hundred hours. G1PSK , clear. Did he say he just made contact with Canada and France? How is that possible? Even my mobile phone is out of range and doesn’t get a signal here in the woods. VHF and UHF frequencies are used for communications with satellites overhead in space; and “ line of sight ” on earth for both base station # and hand held radios working direct to each other – or sometimes over longer distances through nearby repeater stations on hill tops or high buildings. Some repeaters also allow contacts to be made all round the world because they are connected through the internet to other repeater stations in other countries. As well as “ line of sight” (ground wave) , HF allows direct communications all round the world (sky wave). With the right sort of antenna, and conditions, even back pack, and mobile HF rigs can make international contacts. There is a conductive ring of gas 70 to 400 km above the earth called the IONOSPHERE . When the ionosphere is strongly ionised it bends some radio waves back to earth instead of allowing them to escape into space. Signals can therefore bounce repeatedly between ground and ionosphere and travel all round the world. Part of the fun is deciding which band will be open to the part of the world you want to contact. #2 The world is divided into different time zones . To avoid confusion during contacts Radio Amateurs all over the world use UTC (same as GMT) and the 24 hour clock. # Base stations use separate external antennas .