Atec Narda-EA5091-EB5091-EC5091-ED5091 - Manual (Page 2)

NSTS 0807-E0239A-0.0 2 / 3 Subject to change
DESCRIPTION - Shaped Probes
The goal in designing and manufacturing a traditional, “flat” frequency
response probe is to make the probe equally responsive to energy at
every frequency within its rated frequency range. In contrast, Narda’s
patented shaped frequency response probes are designed and
manufactured so that their sensitivity mirrors a particular standard (or
guidance) as closely as possible.
For example, many of the major guidances and standards in the world
set E-field limits for maximum human exposure at 614 V/m (1000 W/m
2 )
at lower frequencies (~1 MHz). At frequencies of 30 to 300 MHz the
limits are typically much less, 61.4 V/m (10 W/m
2 ), a difference of 20 dB
(100 times the power). A shaped frequency response probe designed
for such limits is 100 times more sensitive in the 100 MHz region, than
at 1 MHz.
If you were performing a survey of a site with a flat frequency response
probe that has both of the above frequency ranges and your survey
indicated 137 V/m (or 50 W/m
2 ), it would be difficult to determine if the
site was out of compliance without turning one of the emitters off. Again,
given the example above, the site could be generating anywhere from
5% to 500% of the human exposure limit. There are many sites with
multiple emissions (rooftops, flight lines, broadcast towers) that have
emitters at different exposure limits.
If your interest is general safety measurements, to know if you comply
with an exposure limit or not, you will find shaped probes easy to use in
any environment. The display of total field strength with shaped probes
is not in terms of V/m or W/m
2 , it is “% of Std.” So at a multiple emitter
site, a result of 15% is simple to understand. The total detected field
strength of each emitter (to its limit, at its frequency) has added up to
15%. Besides the ease of use, the main advantage is that you no longer
have the “need to know” the frequency when using a shaped probe.
Table: Standards and matching probe models
Standard or Guidance Level Model
U.S. FCC, 1997 Occupational/ Controlled EA 5091
IEEE C95.1-2005 Controlled Environment EB 5091
Canada Safety Code 6, 1999 RF/Microwave Worker EC 5091
ICNIRP Rec. 1998 Occupational ED 5091