Potomac Instruments FIM-21 - Harmonic Ratio Measurement

www.SteamPoweredRadio.Com
SECTION 2. OPERATION (Cont.)
2.4 Measuring Fie l d Strength (Cont.)
The field meter should always be operated in a vertical position
when making field strength measurements.
After calibrating as described in the previous section, proceed
as follows:
2.5
1. Set the FULL SCALE switch to the range approxi.mating the signal
strength e:xpected.
2. With the FUNCTION switch set at FI, rotate the unit to orient
the loop antenna and obtain maxi.mum deflection on the panel
meter, changing the position of the FULL SCALE switch if nec -
essary to keep the panel meter indication on scale.
3. Read the field intensity directly from the panel meter, using
the position of the FULL SCALE switch as a guide. For example,
with the FULL SCALE switch on 100 mv, a full scale reading of
10 on the m eter means 100 millivolts per meter, and a reading
of 5.6 indicates a field strength of 56 millivolts per meter.
4. Multiply the reading obtained in step 3 by the K factor for
the operating frequency given on the calibration certificate
for the instrument. This procedure is followed when it is
necessary to make full use of the specif i ed accuracy of the
field meter.
5. To de - energize the field meter, rotate the FUNCTION switch
to the OFF position. This disconnects the batteries from
the circuit. Closing the cover also removes the battery
power.
Measuring Harmonic
Ratio in Decibels
Field Strength Ratios may be measured directly in decibels by
reading the db scale of the meter in conjunction with the FULL-SCALE range
indicator. Since each step of the FULL--SCALE switch corresponds to one (1)
decade or twenty (20) db, the ratio is determined by the following formula:
db1 - db2 + N x 20 = Ratio in db
where:
db1 = Harmonic field strength
db2 = Fundamental field strength
N = Number of FULL SCALE steps between f\mdamental
and harmonic