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Scarecrow · July 5th, 2007, 20:55

Text taken from another site:

Penetration and blocking of radio waves
Radio waves are attenuated by almost all objects they pass through, e.g. air, people, trees, buildings and the ground. Dense objects such as earth or metals block radio waves very well. Only a few feet of either can make radio communications impossible. ** However, radio waves also bounce off objects, and this effect can be used to allow communications around corners and inside otherwise impenetrable objects such as steel buildings. Higher frequencies tend to bounce and penetrate more, thus UHF radios are the most suited for work inside buildings and cities. There is a practical limit to this however, and beyond 400-500 MHz the penetration of radio waves starts to fall off again.

Sensitivity
Good receiver sensitivity is an excellent way to make up for low transmit power. Increasing transmitter power takes more energy, and thus translates into shorter battery life on portable radios. Increasing receiver sensitivity usually does not require more power, so this is a desirable characteristic. Most modern radios have excellent sensitivity. Sensitivity is usually measured in microvolts, also abbreviated as uV. The lower the number, the better the sensitivity. A good radio will have a sensitivity of 0.2uV or lower. Up to 0.4uV is acceptable for UHF radios.

** a ham operator once explained to me that it was even possible to bounce or attenuate radio waves in temperature inversion layers in the atmosphere -this also explains non-LOS communications in conditions that are seemingly impossible to explain -again things you cannot see affecting transmission direction as its attenuated and redirected through a temperature layer above your transmission point.

July 5th, 2007, 20:55	#37
Scarecrow A Total Bastard Trader rating Join Date: May 2003 Location: Tottenham	Text taken from another site: Penetration and blocking of radio waves Radio waves are attenuated by almost all objects they pass through, e.g. air, people, trees, buildings and the ground. Dense objects such as earth or metals block radio waves very well. Only a few feet of either can make radio communications impossible. However, radio waves also bounce off objects, and this effect can be used to allow communications around corners and inside otherwise impenetrable objects such as steel buildings. Higher frequencies tend to bounce and penetrate more, thus UHF radios are the most suited for work inside buildings and cities. There is a practical limit to this however, and beyond 400-500 MHz the penetration of radio waves starts to fall off again. Sensitivity Good receiver sensitivity is an excellent way to make up for low transmit power. Increasing transmitter power takes more energy, and thus translates into shorter battery life on portable radios. Increasing receiver sensitivity usually does not require more power, so this is a desirable characteristic. Most modern radios have excellent sensitivity. Sensitivity is usually measured in microvolts, also abbreviated as uV. The lower the number, the better the sensitivity. A good radio will have a sensitivity of 0.2uV or lower. Up to 0.4uV is acceptable for UHF radios. a ham operator once explained to me that it was even possible to bounce or attenuate radio waves in temperature inversion layers in the atmosphere -this also explains non-LOS communications in conditions that are seemingly impossible to explain -again things you cannot see affecting transmission direction as its attenuated and redirected through a temperature layer above your transmission point. __________________ LIKE us on Facebook!!