1. 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.
antenna
2. The AM radio waves are below 2 MHz; these signals follow the
Earth's curvature because they are reflected off the
atmosphere Therefore AM radio signals in low-noise environments
can be received by radios that are way below the horizon hundreds
of miles away Whereas two-way radios usually fall in the frequency
range of 150MHz to 900MHz; these frequencies antenna travel in
straight lines
3. Radio waves can be reflected, or bounce off surfaces so the straight
line between radios, may not always be so straight Anyway as a
general rule these waves cannot travel over the horizon or behind
solid obstacles Because of this reason, you have to factor in
antenna height as well for sending signals farther
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 more
range
6. Generally, to get more gain you need a bigger antenna A simple
"quarter wave" (0 dB, or unity gain) antenna for VHF is about 18
inches long A 3 dB antenna for the same frequency would be about
4 feet long, while a 5 dB antenna is maybe 8 feet
7. For UHF, a quarter wave is six inches, and a 5 dB about 2 feet
Lower the frequency, longer the antenna If you're using the 3
inch stubbies on a UHF portable, you might see a difference going to
the six inch rubber duck
8. Theoretically the longer antenna is better Directional antennas
achieve 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 typical
shark fin is an example of a log periodic antenna) A higher level
signal helps improve the signal to noise ratio by overcoming the
noise induced in an antenna cable, but a signal that is too high can
cause problems at the receiver
9. This is why antenna amplifiers typically have jumper settings to
apply the proper amount of gain needed to compensate for loss in a
cable of particular type and length There are other factors that
affect the range of a two-way radio too such as weather, exact
frequency used, and obstructions