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  1. 1. An antenna is a significant part of any two way radiosystem. No radio can outperform its antenna. Many times users have been able to improve theperformance of a communications system merely by improving the antennas.antenna
  2. 2. The AM radio waves are below 2 MHz; these signals follow theEarth's curvature because they are reflected off theatmosphere Therefore AM radio signals in low-noise environmentscan be received by radios that are way below the horizon hundredsof miles away Whereas two-way radios usually fall in the frequencyrange of 150MHz to 900MHz; these frequencies antenna travel instraight lines
  3. 3. Radio waves can be reflected, or bounce off surfaces so the straightline between radios, may not always be so straight Anyway as ageneral rule these waves cannot travel over the horizon or behindsolid obstacles Because of this reason, you have to factor inantenna height as well for sending signals farther
  4. 4. Antenna gain is measured in decibels, or dB A 0 dB antenna(sometimes called a "unity" gain antenna), is an antenna with no gain More gain on an antenna will, usually but not always, give you morerange
  5. 5. Generally, to get more gain you need a bigger antenna A simple"quarter wave" (0 dB, or unity gain) antenna for VHF is about 18inches long A 3 dB antenna for the same frequency would be about4 feet long, while a 5 dB antenna is maybe 8 feet
  6. 6. For UHF, a quarter wave is six inches, and a 5 dB about 2 feetLower the frequency, longer the antenna If you're using the 3inch stubbies on a UHF portable, you might see a difference going tothe six inch rubber duck
  7. 7. Theoretically the longer antenna is better Directional antennasachieve much of their gain by rejecting pick-up from certain areas,such as the sides and rear in the case of a log periodic (the typicalshark fin is an example of a log periodic antenna) A higher levelsignal helps improve the signal to noise ratio by overcoming thenoise induced in an antenna cable, but a signal that is too high cancause problems at the receiver
  8. 8. This is why antenna amplifiers typically have jumper settings toapply the proper amount of gain needed to compensate for loss in acable of particular type and length There are other factors thataffect the range of a two-way radio too such as weather, exactfrequency used, and obstructions
  9. 9. The radio's power output has a factor too
  10. 10. antenna