channel station. The null is bi-directional, however, sometimes limiting the measurement
effectiveness when the station’s antenna pattern null is in a reciprocal direction to the
station being protected.
Both the measurement monopole and shielded loop antennas cover the full AM Broadcast
band and are relatively stable over a variety of environmental conditions.
Antenna factors
Calibrated measurement antennas are provided with calibration tables to normalize NIST
traceable RF field strength measurements throughout the industry. By using NIST
traceable antennas, field strength meters, and other traceable components, manufacturers,
users, and the FCC can communicate signal values without the necessity of shipping
measurement equipment or designing it to some theoretical specification. Calibrated
measurement antennas are individually range-measured and supplied with correction
values for frequencies of interest. When these correction factors are added to similar
factors for connecting cables, filters, etc., the total ‘antenna factor’ may be used as a field
strength correction factor to convert measured values directly into field strength in
dBuV/m indicating the real, available RF field.
Field Strength Meters
Modern field strength
meters such as the
Z Technology R-506 and
R-507 are calibrated and
traceable to NIST over the
specified operating range.
Because these instruments
contain microprocessors
and memory to store and
recall calibration data, field
calibration is not required.
Both the R-506 and R-507
(which includes a spectrum
display capability for
television measurements) may be used with a BC-BCB calibrated block converter (shown
here attached to the front of the field strength meter) for AM Broadcast measurements.
Power is accepted at the instrument’s 50-ohm input and power levels are reported in the
desired dBm, dBuV, or with the antenna factor, field strength directly in dBuV/m. Older
designs report in uV, which is the antilog of dBuV divided by 20. A units conversion
table is provided as Appendix C.
Z Technology field strength meters are fully programmable and may be operated in a
system under a Windows application to measure, view, and document field strength
related values. Software applications supplied with the field strength meter can automate
the measurement of multiple stations, record GPS locations, graphically display
measurements, and record data for export to other applications. Modern field strength
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