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Radio waves travel from one point to another by several different means. The general term for these methods of wave travel is "Propagation".

You may know that "short-wave" broadcast signals can be propagated over distances of several thousand miles by reflection off upper regions of the atmosphere. This can give CB radio operators the "advantage ?" of being able to talk to the USA on 4 watts power, when conditions are right. Two-way radio, on the other hand operates on Low Band VHF (68 - 88Mhz), VHF (134-174MHz) or UHF (420-470MHz) band. On these bands, radio waves generally do not reflect off the ionosphere; instead the radio waves behave almost like light waves and they travel in a straight line, and when they meet a building or obstruction, they go no further in that direction. The effect is more pronounced the higher in frequency that you go, but with more reflections and less absorbtion at higher frequencies. As a generality the lower frequencies go furthest, but are more subject to interference Hence for a rural Farmer or vets practice you would generally recommend a Low bBand VHF system, whilest for a security firm in a city centre a UHF system.

Therefor, when operating a VHF or UHF radio, it is best for you to be as high and free from obstructions as possible, so as to cover the greatest distance. If you operate a handportable radio from inside a car or building, the surrounding metal can be expected to absorb a significant amount of signal (both transmitted and received). Coverage may therefor be very poor under these conditions. Moving closer to a window will, of course, improve the situation in many cases, or indeed using an external aerial attached to the portable radio. Hence the best performaning radio base stations are located on hill tops or high buildings.

Because radio waves at VHF and UHF are similar (in many ways) to light waves, they will reflect off hills and buildings to some degree. In a crowded urban area , with buildings close together, these reflections can cause rapid variations in signal strength as you walk or drive variations in signal strength as you walk or drive around. Therefore, if a signal is very weak, try walking a few feet in any direction. Reception may suddenly become clear, as a particular reflection path becomes dominant. Such reflections are frequently useful, as they may allow communications between two stations over a highly-obstructed path.

The effects of multipath reflections and fading become more pronounced the higher in frequency that you go, which results in the common phenomena of Cellphone St Vitus Dance !, as the hapless cellphone user tilts and jerks his head from side to side in an effort to find the best signal, in an enviroment where the signal strength is changing continually due to different reflectios as objects move around the phone user.

Always hold the radio up high, near your mouth, while transmitting. In this way, the antenna is high and in the clear, and coverage is best.

You will also note a significant reduction in radio performance if you use a remote speaker mic, with the radio strapped to your belt. Although you may have the convenience of the small handheld microphone, the radio waves are greatly absorbed by your body! May professional users of radio solve this problem with a "Public safety microphone" ( available for high tier products like the GP900 / GP1200 ) this remote microphone has the radio antenna mounted on top it, and can often been seen used by policemen.

 

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Last modified: February 09, 2006