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Welcome to this issue of
“MID-MAIL”. I
would like to take a few minutes to discuss the fallacies of
radio range. Many aggressive marketers publish radio range
specifications “ up to a 5 mile radius”. Lets break this
statement down to its components.
To
start with radius means the distance from the center of a
circle to its circumference. With this definition, the
actual 5 mile radius transmit range has just been cut
to just 2˝ miles. The next part is even cleverer. That is,
“Up to,” does not guarantee that range. If you are on a
flat piece of land, with NO
obstructions, ( Hills, Trees, Buildings ) nothing over 5
foot in height between you and the person you are trying to
communicate with, and you have a strong tail wind. It is
possible to communicate that distance. Add a tree and your
range for reliable communication has just diminished.
The
truth is, there are many factors to consider when
determining coverage area. Typography and obstructions are
only two. Other factors are power, height, gain and loss.
Let’s take a look at power.
Power is synonymous with output (or
watts). Power is the transmit capability of each radio. It
is perceived that if you double your power you will double
your range (i.e., a 4-watt radio will transmit twice as far
as a 2-watt radio). Although this scenario seems logical, we
all know logic is not always the correct answer. Again,
depending on the combinations of other factors, a rule of
thumb would be, double your power, receive 30-35% more
range.
Height
is probably the single most important factor in determining
range. The higher your antenna the greater the area of
coverage. Unlike
power which only deals with the transmission of signals,
height has a direct bearing on both the transmit and receive
portion of propagation. Increasing your height can increase
your coverage area up to 75%.
Gain
addresses
the increase of
signal, and is measured in decibels (dB). It is determined
by comparing one power level to another. When working with
gain, for every 3dB of signal gain you effectively double
your power. For example. If you have a 2 watt transmitter
with a gain of 3dB through an amplifier or your antenna your
effective power output would increase from 2 watts to 4
watts, if you had a gain of 6db your output would increase
to 8 watts (2 x 2 x 2 = 8).
Loss
works in reverse of gain; it affects the amount of signal
that is lost. Same 2-watt transmitter but you have a signal
loss from your antenna or coaxial cable of 3dB, your
effective power output would decrease 50% or 1 watt. Loss
can also come from foliage or building penetration and will
degrade the amount of signal your radio will receive in the
same way.
Many
companies find that they have satisfactory coverage from
edge to edge, but that there are transmission voids with-in
their coverage area. We call these “dead spots”.
Dead
spots are areas where radio signals can not penetrate or
escape from. Machinery, building materials or a multitude of
other reasons may shield these areas. Repeaters, various
types of cable, amplifiers and properly designed antenna
arrays are all ways to compensate for these losses and
guarantee 100% reliability of your communication system.
As
you can see there is not a single correct answer to all
coverage needs. Every application is different. Therefore
each requirement must be examined to determine which will
best suit your needs.
We hope you find this issue of "Mid-Mail"
informative. As always, if you need any questions
answered or if there is a subject you would like to see us
address, just use the feedback link at the top of the
newsletter.
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