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An-Antenna-Is-A-Significant-Part-Of-Any-Two-Way-Ra41 An-Antenna-Is-A-Significant-Part-Of-Any-Two-Way-Ra41 Document Transcript

  • An antenna is a significant part of any two way radio system. No radio can outperform its antenna. Many times users have been able to improve the performance of a communications system merely by improving the antennas.dipole
  • The AM radio waves are below 2 MHz; these signals follow the Earth'scurvature because they are reflected off the atmosphere Therefore AM radiosignals in low-noise environments can be received by radios that are waybelow the horizon hundreds of miles away Whereas two-way radios usuallyfall in the frequency range of 150MHz to 900MHz; these frequencies travel instraight lines
  • Radio waves can be reflected, or bounce off surfaces so the straight linebetween radios, may not always be so straight Anyway as a general rulethese waves cannot travel over the horizon or dipole behind solid obstaclesBecause of this reason, you have to factor in antenna height as well forsending signals farther
  • Antenna gain is measured in decibels, or dB A 0 dB antenna (sometimescalled a "unity" gain antenna), is an antenna with no gain More gain on anantenna will, usually but not always, give you more range
  • Generally, to get more gain you need a bigger antenna A simple "quarterwave" (0 dB, or unity gain) antenna for VHF is about 18 inches long A 3 dBantenna for the same frequency would be about 4 feet long, while a 5 dBantenna is maybe 8 feet
  • For UHF, a quarter wave is six inches, and a 5 dB about 2 feet Lower thefrequency, longer the antenna
  • If you're using the 3 inch stubbies on a UHF portable, you might see adifference going to the six inch rubber duck Theoretically the longer antenna isbetter
  • Directional antennas achieve much of their gain by rejecting pick-up fromcertain areas, such as the sides and rear in the case of a log periodic (thetypical shark fin is an example of a log periodic antenna) A higher level signalhelps improve the signal to noise ratio by overcoming the noise induced in anantenna cable, but a signal that is too high can cause problems at the receiver
  • This is why antenna amplifiers typically have jumper settings to apply theproper amount of gain needed to compensate for loss in a cable of particulartype and length There are other factors that affect the range of a two-wayradio too such as weather, exact frequency used, and obstructions
  • The radio's power output has a factor too
  • dipole