Software Newsletter #32 - December 17, 2006
Racing Computers and Software - www.iFamilySoftware.com
1. The Truth About Paging Systems
The Truth About Paging Systems --
The Watts Question
will say that more power (wattage or watts) into a system means the system works
better over a longer distance. To better understand the "watts question," one
must understand the difference between the power into a transmitter and the power
out (radiated power). The power into the transmitter is the number salespeople
often use to sell their product. However, the radiated effective power from the
transmitter's antenna is the power that counts. The FCC strictly regulates the
amount of power radiated by the antenna. No legal wireless system can radiate
more power than the FCC allows. For a non-licensed channel, this is a maximum
of 2 watts of output power. The internal design of the transmitter determines
how well the transmitter converts input power into output power. To further complicate
the "watts question," all radiated power is not necessarily useful power. Many
"cheap" designs radiate a lot of power, but the power is distributed over several
frequencies to which the receiver (pager) is not listening. The "useful energy"
would be that energy that is on the correct frequency for the system. To radiate
power most efficiently, a transmitter should have an antenna that is ¼ or ½ wavelength
of the frequency. Thus, the antenna length is an important factor as discussed
in the frequency portion of this article. We have discovered a vast difference
between transmitter designs, both in power efficiency and in useful radiated energy.
pager receivers vary in their signal sensitivity. Receiver sensitivity could be
compared to a person's ability to hear. Well-designed receivers are able to discern
messages at energy levels far below what less sensitive receivers are able to
pick up. In technical terms, receivers can be broad band lower gain or narrow
band higher gain by design. The FCC does not regulate the efficiency or sensitivity
of receivers; they only regulate the maximum spurious radiation coming from the
pagers as a result of the electronic circuits inside. Receiver sensitivity alone
can easily be responsible for causing one system to work twice as far as another.
Finally, the third
factor to consider when calculating the range of a wireless system is frequency.
There are different frequencies on which the systems operate. Currently there
are two groups of systems: those operating at 27 MHz and those operating in the
450 MHz to 470 MHz range (UHF). The FCC has different power output rules for the
two groups. The only legal systems that radiate 7 watts from the output stage
are 27.255 MHz transmitters, also known as the Citizens Band Channel 23. As described
earlier, to effectively radiate this power from an antenna, the antenna should
be at least ¼ wavelength long. However, ¼ wavelength at 27 MHz is 8 feet. Remember
that both the transmitter and the receiver need an antenna. None of the 27 MHz
systems have 8-foot antennas as this would be impractical. All manufacturers compromise
the antenna design to fit in a smaller package using various forms of antenna
loading, which affects the efficiency of the transmitter and the receiver. We
have found the range of the 27 MHz we have tested to be less than the UHF systems.
Generally the longer-range pagers are UHF systems. The UHF systems operate in
the 450 to 470 MHz range. They all have approximately 2 watts applied to
the output stage that radiates the power to the vibrating pagers. The FCC controls,
licenses, and limits the amount of radiated power from transmitters. A ¼ wavelength
antenna for a 450 MHz system is approximately 6.5 inches. Even on these systems,
designers use some antenna loading, but they tend to radiate power much more efficiently
because the antennas are closer to the ideal length. In addition to the above
considerations, there are many theoretical equations that govern the propagation
of radio frequency energy through air and through materials. The Scope UHF system
is the best designed and most efficient system we have ever seen. Our engineers
have tested several UHF systems from other companies and have never found one
that compares to the Scope system.
Our Scope Paging System will broadcast
cleanly for up to a five (5) mile radius with our external dipole (1/2
wave) antenna and at least a one (1) mile radius with the standard (1/4
wave) antenna. I've seen some of the others that will not transmit cleanly at
Englishtown, NJ, for even a 1/2 mile to the staging lanes. So much for false advertising
claims concerning wattage!
World Technical Support --
Family Software, you'll get better technical support than anywhere on the planet.
Why? Because, we design and/or use all of the products that we sell. All of my
35+ years of on-track racing experience and knowledge is available to you. Try
to find that kind of information at any one of our competitors. You won't be able
to, I guarantee it! Family Software cares about the racer and his/her success
as a racer. We also want you to get the most value for your hard earned dollars.
-- Secure Ordering --
can safely order directly from our web site. All of your information is handled
the web site. Our company is registered with the Public Eye for safe, secure ordering.
Family Software - Drag Racing Computers and Software
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