TM 11-6625-486-14&P
above is multiplied by the appropriate harmonic number
If F1 and F2 are in megahertz, Fx will be in megahertz.
(h above) to determine the exact transmitter frequency.
f. To verify the frequency found above,, find two
other zero beat points and substitute these values in the
equation above.
3-6. Determining Frequency of Distant Transmitter
NOTE
This measurement requires the use of a radio receiver
As an example of using the formula,
in conjunction with the frequency meter.
If the
consider the case where beat notes
transmission is continuous wave (cw), use either a
receiver with a beat-frequency oscillator (bfo) (a below)
are obtained at 30, 40, and 60 MHz.
or a regenerative receiver (b below). If the transmission
The two loudest beat notes are
is other than cw, tune in the transmitter signal.
obtained at 40 and 60 MHz.
Determine the approximate frequency from the receiver
Substituting these two frequencies in
dial.
the formula we obtain:
a. If the transmission is cw and a receiver with a
bfo is used, proceed as follows:
(1) Turn on the bfo.
(2) Tune the receiver to a zero beat.
g. Set the RANGE SW to the appropriate range for
(3) Note the approximate frequency.
the frequency found above.
(4) Turn off the bfo before proceeding.
h. If the frequency found above is not in the
b. If the transmission is cw and a regenerative
fundamental frequencies covered by the RANGE in use,
receiver is used, proceed as follows:
find the estimated transmitter frequency in an harmonic
column in the calibration tables and obtain the
(1) Turn up the regeneration control until the
fundamental frequency to be set on the filmstrip (para 3-
receiver oscillates.
(2) Tune the receiver for zero beat.
transmitter frequency by the appropriate number to
(3) Note the approximate frequency.
obtain a frequency in the fundamental range of the dial.
(4) Turn down the regeneration control before
i. Set the FUNCTION SW to CHK.
proceeding.
NOTE
c. Set the RANGE SW according to the frequency
When
performing
the
check
found above. If the frequency is not in the fundamental
procedure, do not connect the
frequencies covered by the RANGE in use, find the
frequency meter antenna.
fundamental frequency in the calibration tables (para 3-
j. Adjust the TUNING control to bring the
appropriate number to obtain a frequency in the
checkpoint (nearest to the desired fundamental
fundamental range of the dial.
frequency) under the hairline indicator. Adjust the
d. Set the FUNCTION SW to CHK.
CORRECTOR control for a zero beat.
NOTE
k. Set the FUNCTION SW to OPER and connect
When
performing
the
check
the frequency meter antenna to the ANT. connector and
procedure, do not connect the
place the antenna near the transmitter.
frequency meter antenna.
of the desired fundamental frequency and listen for an
e. Adjust the TUNING control to bring the
audio beat note. If several notes are heard, tune the
checkpoint (nearest the desired fundamental frequency)
frequency meter to the strongest beat note; then, tune
under the hairline indicator. Adjust the CORRECTOR
the frequency meter on both sides of this frequency for
control for zero beat.
a zero beat.
f. Set the FUNCTION SW to OPER. Connect the
frequency meter antenna to the ANT. connector and
above was a fundamental frequency of the range being
place the antenna close to the receiver antenna lead.
used, then the reading obtained in l, above gives the
g. While listening to the receiver through the
exact transmitter frequency directly. If the transmitter
receiver headset or loudspeaker, tune the frequency
frequency computed in e above was a harmonic in the
meter in the region of the receiver frequency setting
range being used, the fundamental frequency obtained
until a beat note or whistle is heard; then, tune the
in l above is located in the calibration tables and the
frequency meter for a zero, beat or as near to a zero
exact transmitter frequency is obtained from the
beat as possible.
appropriate harmonic column.
If the transmitter
h. If the transmitter frequency obtained in g above
frequency computed in e above was a harmonic in the
was a fundamental frequency of the range being used,
range being used and the calibration tables are not
then the reading obtained in g above
being used, the fundamental frequency obtained in I
3-7
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