Instruction manual

proof of performance or field strength measurements are to be made, AM Stations should
bypass any processing that makes the audio modulating waveform intentionally non-
symmetrical. Bypassing audio processing allows a true picture of Carrier Shift, Audio
Distortion, Power Output, and Field Strength.
Organizing AM Field Strength Measurement Tests
Once the fundamentals of an AM broadcast signal are understood, signal coverage testing
can be addressed. Assembling a measurement system for AM field strength testing is the
next step. Such a system will normally consist of the following items:
Calibrated AM Receiving Antenna with Antenna Factors
30dB Attenuator Pad (optional)
Low Frequency Block Converter
Field Strength Meter or a Drive-Test System
Laptop PC with Windows measurement application (optional)
GPS Receiver (optional)
By understanding how these tools operate together as a measurement system useful and
accurate signal coverage information can be quickly gathered, analyzed and recorded.
Field Strength Measurement Antennas
The measurement receive antenna is physically small compared to the AM Broadcast
transmitting antenna. Measurement antennas are individually range calibrated and
supplied with an Antenna Factor correction table providing traceability to the National
Institute of Standards and Technology.
There are two common measurement antennas for AM Broadcast measurements:
The amplified monopole antenna, such as Z Technology’s AA-2R, consists of a
ruggedized one-meter vertical rod
mounted on a base containing an
impedance-matching amplifier, in
turn mounted on a small
counterpoise. The mounting of this
antenna is quite tolerant and it may
be attached by its counterpoise to a
grounded or ungrounded tripod,
directly to the metal top of a vehicle,
or handheld. This short vertical
antenna is convenient and non-
directional for measurements while
stopped or driving.
A second popular measurement antenna is the shielded
loop. This type of antenna is not as sensitive as the
vertical rod antenna, and may be more tolerant of
atmospheric noise. It does exhibit a deep null of from
20 – 25 dB that can be oriented to minimize
interference from a point-source noise or a distant co-