Instruction manual

TM 11-6625-3017-14
lock-plate secured by two screws above the switch, slide
the switch button into its other position (as shown on the
panel), reverse and replace the lock-plate to hold the
button in its new position. No other adjustment is
needed.
Switch the MAINS -BATT switch Lo MAINS.
2.2.2 Battery operation
The modulation meter also works on 24 V batteries. A
suitable supply would be a 24 V positive earth vehicle
battery, on or off charge. Negative earth systems must
not be used on any account, since the case of the
instrument and its coaxial connections would be live. If a
positive earth supply is not available, use dry cells. Six
4.5 V batteries, e. g. Exide type H30 or 3DT9, giving 27
V initially, should give several hours of service before
their output drops below 21.5 V. This is equivalent to
several weeks in normal use provided that the instrument
is switched off as soon as the measurement is
completed. Current drain is 350 mA approximately.
Observe correct polarity when connecting batteries to the
back panel terminals; left is positive.
Switch the MAINS-BATT switch to BATT.
2.3 CONTROLS
The following outline of control functions is intended
for reference purposes. Until you are familiar with the
instrument, use the operating procedures detailed in later
sections.
(1) Oscillator tuning dial. Shows effective internal local
oscillator frequency.
(2) OSCILLATOR TUNE controls. (Outer: coarse - inner
: fine). Adjust for dial reading 1.5 MHz above signal
frequency. Inoperative when using external local
oscillator.
(3) CRYSTAL sockets. Accept style D miniature
crystals for local oscillator control.
(4) EXT OSC socket. Type BNC: Accepts external
local oscillator signal of about 100 mV.
(5) CRYSTAL switch. Selects crystal required.
Switch to OFF when not crystal controlled.
(6) RANGE switch. Selects internal local oscillator
ranges as shown beside tuning dial, or external
oscillator.
(7) R. F. IN socket. Type BNC. Accepts signal
under test.
(8) I. F. OUT socket. Type BNC. Connect to
counter for measuring carrier shift or to
oscilloscope for viewing unfiltered a.m.
envelope. Output is 1.5 MHz at about ½ V.
(9) LEVEL control. Adjusts attenuation of signal
input at R. F. IN socket.
(10) SET A.M. level control. Adjust for SET reading
on meter when Function selector is at SET A.
M.
(11) Function switch. Selects setting up and
measuring conditions on f.m. and a.m. Numbers
show normal sequence of settings.
(12) A. M./DEV RANGE switch. Selects full-scale
meter range, six for f. m., two for a. m.
(13) MAX MOD FREQ switch. Selects modulation
bandwidth in f.m. measurements.
(14) OUTPUT terminals. Provide demodulated
output for connection to extra-sensitive meter,
wave analyser etc.
(15) Meter. Reads % a.m. depth and f.m. deviation.
R.F. LEVEL arc applies to position 1 of Function
switch, and SET mark to the four SET positions.
(16) SET CAL F.M. preset. Standardizes deviation
measuring accuracy. Adjust for SET reading on
meter with Function switch at SET CAL.
(17) DE-EMPHASIS switch. Applies deemphasis to
demodulated signal at OUTPUT terminals.
Does not affect meter readout, except on 1.5
kHz deviation range.
(18) SUPPLY switch. Shows red segments when on.
Works on both mains and battery operation.
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