TM 11-6625-486-14& P
readout frequency by the desired harmonic number.
3-5.
Determining Local Transmitter Frequency
Conversely, the correct dial setting for any given
When Approximate Frequency is Unknown
harmonic frequency can be found by dividing the
a. Use either an absorption-type wavemeter or
harmonic frequency by any number that will give a
radio receiver to determine the approximate frequency,
fundamental frequency within the range of the frequency
and then follow the procedure given in paragraph 3-4. If
meter filmstrip. In general, use the lowest harmonic
the above equipment is not available, follow the
number that will yield the desired frequency.
procedures given in b through m below.
CAUTION
Determining Local Transmitter Frequency
Do not couple the frequency meter
When Approximate Frequency is Known
antenna directly to the transmitter
a. Set the RANGE SW to the appropriate
output.
The correct separation
frequency range.
If the frequency is not in the
between the transmitter and the
fundamental frequencies (125 to 250 kHz, 2.5 to 5.0
frequency
meter
antenna'
will
MHz, or 65 to 130 MHz) covered by the RANGE in use,
depend on the amount of power
find the frequency in an harmonic column in the
being radiated. Place the frequency
calibration tables and obtain the filmstrip setting from
meter antenna as far away from the
the FREQUENCY column (para 3-3 c). If not using the
transmitter as possible, and then
calibration tables, divide by a number to obtain a
start moving the antenna closer for
frequency in the fundamental range of the filmstrip.
the desired result.
b. Set the FUNCTION SW to CHK.
NOTE
b. Set the FUNCTION SW to OPER and connect
When
performing
the
check
the frequency meter antenna to the ANT. connector.
procedure, do not connect the
Place the antenna near the transmitter.
frequency meter antenna.
c. Turn the frequency meter TUNING control from
the high end of the range toward the low end and listen
c. Adjust the TUNING control to bring the
for strong beat notes. Select the two adjacent beat
checkpoint (nearest to the desired fundamental
notes that have the loudest sound and zero beat on
frequency) under the hairline indicator. Adjust the
each adjacent beat note.
Record the filmstrip
CORRECTOR control for a zero beat.
frequencies for these two points.
CAUTION
d. When several beat notes are heard, it indicates
Do not couple the frequency meter
that consecutive harmonics of the vfo are beating
antenna directly to the transmitter
against the unknown frequency; for example, if the
output.
The correct separation
unknown frequency is 120 MHz, the fifth harmonic of 24
between the transmitter and the
MHz, the fourth harmonic of 30 MHz, and the third
frequency meter antenna will depend
harmonic of 40 MHz would be heard.
on the amount of power being
e. Take the two zero beat points recorded in c
radiated. Place the frequency meter
above and substitute these two frequencies in the
antenna far from the transmitter, and
following equation:
then start moving the antenna closer
for the desired result.
Fx = F1 X F2
F2 - F1
d. Set the FUNCTION SW to OPER and
connect the frequency meter antenna to the ANT.
Fx = Unknown frequency
connector and place the antenna near the transmitter.
F2 = Highest zero beat point
e. Tune the frequency meter in the
immediate area of the estimated frequency and listen
F1 = Lowest zero beat point
for an audio beat note. If several beat notes are heard,
tune the frequency meter to the strongest beat note;
NOTE
then, tune the frequency meter on both sides of this
frequency for a zero beat.
Always use the exact frequencies
indicated on the filmstrip.
f. If necessary, locate the frequency found in e
above, in the FREQUENCY column of the calibration
If F1 and F2 are expressed in kilohertz, Fx will be in
tables. At the intersection of this frequency and the
kilohertz.
harmonics column, read the frequency of the signal
being measured. If the calibration tables are not used,
multiply by the number used in a above.
3-6
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