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RF Exposure
Measurements & Testing Cell Towers Part 3
Life Bluetube Headset
Cell Phone Radiation Protection
Mobile Phone Radiation Protection
Trifield Electromagnetic Field Meter
Technical Challenges for RF Site Surveys
Measurement of the emissions from cell towers presents
particular technical challenges beyond those encountered for
broadcast antenna sites. To understand these challenges, a
few comments about radio frequency measurement are required.http://www.emfnews.org/store/home-cell-phone-and-mobile-tower-radiation-meters.html
Protocols for the measurement of RF energy for the purpose
of human exposure assessment often recommend the use of an
"isotropic broadband probe" because this type of sensor
responds equally to energy arriving from any direction, and
over a broad frequency range, as does the human body. These
instruments are commonly used because they permit a quick
and simple measurement. Unfortunately, some of the meters
used for typical RF compliance surveys are unable to
accurately measure the low power densities present at some
cell sites. An alternate approach is required.
A related problem involves the concurrent presence of other
signals besides those from the cell phone system. The
"broadband" characteristic of the isotropic broadband probe
means that it will measure any signals across a wide range
of frequencies. The reading produced by the instrument will
be the combination of all signals present. In a large number
of cases, the other signals present near a cell tower will
be as strong as the cellular signals that one is trying to
measure. Realistically, this composite measurement of all
signals may be the most relevant exposure metric, but an
interpretation of the significance of a reading sometimes
requires that one know the frequency of the signal that
produced it. For instance, is it FM, TV, cellular, or
something else?
One of the most significant RF measurement problems, and one
responsible for some of the greatest inaccuracy, involves an
instrument erroneous response that can occur when there are
two or more strong signals present at the same time. A very
large proportion of antenna sites (cell and broadcast) now
have multiple strong signals. Instrument design can minimize
this problem, but many of the commonly used isotropic
broadband meters perform very poorly in this multi-signal
environment. The result is a reading that is much higher
than actual, sometimes double (100% error).
An additional challenge results from the fact that power
density levels at a cell tower site are not always constant,
as they usually are at a broadcast antenna site. People use
their cell phones more at some times of the day, and on some
days of the week, than at others. The cellular service
providers maintain additional capacity in the form of
multiple channels which will become active as needed to meet
demand. Each active channel adds to the measured power
density at the cell site. The variable nature of power
density levels at some sites must be taken into account.
When necessary, we employ timed signal averaging or data
logging to produce an accurate assessment.
RF measurement surveys conducted by EMF Services employ
procedures and equipment to address each of the challenges
noted above.
A spectrum analyzer is used for identification of RF
sources, and for assessment of the relative magnitude of
signals in different frequency ranges. The use of this
instrument with a calibrated antenna will allow a sensitive
and precise "channel power measurement" across selected
frequency ranges, or measurement of the strength of an
individual signal. In some cases, we also use a high
sensitivity isotropic broadband probe for measurement of the
composite power density. Our comprehensive analytical report
summarizes all this data in a concise and understandable
format, but includes an Appendix with detailed site data,
such as the spectrum analyzer plots shown below.
Suriname Paramaribo
New Orleans, Louisiana
Libya Tripoli
Libya, Tripoli
Mauritius, Port Louis
Bulgaria Sofia
Lithgow Australia
Latvia Riga
Washington, District of Columbia
Elizabeth New Jersey USA
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