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.
dipole
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 travel in straight
lines Radio waves can be reflected, or bounce off surfaces so the
straight line between radios, may not always be so straight
3. 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
Antenna gain is measured in decibels, or dB A 0 dB antenna
(sometimes called a "unity" gain antenna), is an antenna with no gain
4. More gain on an antenna will, usually but not always, give you more
range 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
5.
6. 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 Theoretically the longer antenna is better
7. 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 This is why
antenna amplifiers typically have jumper settings to apply the proper
amount of gain needed to compensate dipole for loss in a cable of
particular type and length
8. There are other factors that affect the range of a two-way radio too
such as weather, exact frequency used, and obstructions The
radio's power output has a factor too
