Instruction manual

TM 11-66253017-14
2.4 PREPARATION FOR USE
It is helpful in reading these instructions and in using
the instrument until completely familiar with its operation,
to remember that where a control or switch position is
marked SET, the control should be adjusted to make the
meter read on the line marked SET.
Before commencing measurements:
(1) Check the mechanical zero of the meter and
adjust, if necessary, by means of the screw.
(2) Turn the LEVEL control towards minimum
(counter-clockwise).
(3) Connect the signal to be tested to the R. F. IN
socket at a level which, operating into50 1, will
develop a voltage within the limits given in
section 1.2 under ’R. F. input’ .At the highest
carrier frequencies the shortest possible input
lead should be used or an external 50 f matching
attenuator.
CAUTION Inputs greater than 3 V r. m. s. May damage
the attenuator. If in doubt, use an external attenuator.
(4) Turn the SUPPLY switch clockwise so that the
red segments show.
2.5 MEASURING F.M. DEVIATION
After carrying out the preparation procedure in
section 2.4:
(1) Set the A.M. /DEV RANGE switch (below the
meter) to suit the expected deviation of the
signal under test.
(2) Set the MAX MOD FREQUENCY switch to 200
kHz unless the modulating frequency is less than
15 kHz. If so, switch to 15 kHz in order to obtain
the best signal-to-noise ratio.
(3) Set the DE-EMPHASIS switch as required. Its
setting has no effect on the internal meter
reading unless the A.M. /DEV RANGE switch is
in the 1.5 kHz deviation position. The de-
emphasis is effective on the demodulated signal
at the OUTPUT terminals.
TABLE 2.1.
Frequency ranges
RANGE switch Range Osc. freq. R.F. input freq.
setting MHz MHz
1-2 1 5.5 -11 4.0 - 9.5
2 11 - 22 9.5 - 20.5
3-4 3 22-44 20.5 - 42.5
4 44.-.88 42.5 - 86.5
5-8 5 88-176 86.5 - 174.5
6 176- 352 274.5 - 350.5
7 352-704 350.5 - 702.5
8 701.5-1001.5 700 - 1000
EXT - F+ 1.5 F
(4) Set the oscillator RANGE switch in accordance
with table 2.1. For detailed instructions on
oscillator arrangements, see section 2.10. In
this section, it is assumed that the internal local
oscillator will be used.
(5) Set the Function switch to TUNE OSCILLATOR
AND ADJUST LEVEL. Adjust the OSCILLATOR
TUNE dial to a frequency 1.5 MHz above the
carrier. Tune for peak meter deflection, and
then adjust LEVEL for a meter deflection in the
black R. F. LEVEL arc, preferably near the top
end for best signal-to-noise ratio.
(6) Set the Function switch to F.M. SET FREQ.
Slightly readjust the OSCILLATOR TUNE control
until the meter deflects to the SET line. Avoid
spurious settings - the correct one is the closest
to the original setting obtained in (5).
(7) Set the Function switch to DEV + and DEV-.The
demodulated peak frequency deviations above
and below the carrier frequency may be
measured on the meter or viewed on an
oscilloscope connected to the OUTPUT
terminals. Read the meter on the scale
corresponding to the setting of the A. M./ DEV
RANGE switch.
Note If unequal readings are obtained, distortion in the
equipment under test is indicated.
See section 2.12.
(8) Before carrying out a series of measurements,
and from time to time during measurements,
2-4