TM 11-6625-255-141/TO 33A1-13-170-1
NOISE, algebraically add -40 dBm to the com-
c. Set the function switch to SET LEVEL for a
puted reading. For example, if the computed
20-dB gain (or for a voltage gain of 10) or to
meter reading is -18 dBm and the function switch
NOISE for a 40-dB gain (or for a voltage gain of
is set to NOISE, algebraically adding 40 dBm to
-18 dBm gives a true reading of -58 dBm.
d. Set the meter range switch to 10 R.M.S.
311. Use of Oscilloscope With Spectrum
e. Slowly advance the signal INPUT control. If
the meter reading exceeds 10 before the control is
turned to MAX, do not use increased sensitivity
formation about the signal source under test can
to make the measurement. When this condition
be obtained. The oscilloscope provides the opera-
exists, make rms voltage readings as described in
tor with information about the signal source that
could give erroneous readings on the spectrum
analyzer. Noise, hum, parasites, stray field pick-
f. Set the signal INPUT control to MAX and
up, or any other form of extraneous signals will be
the meter range switch to R.M.S. VOLTS (g be-
indicated on the oscilloscope. The oscilloscope is
low) or DB ( h below) to obtain the most readable
and may be used with measuring techniques de-
g. Compute the voltage reading as described in
SET LEVEL, divide the computed reading by 10.
If the switch is set to NOISE, divide the com-
312. Stopping Procedure
puted reading by 100.
a. Turn the power switch to OFF.
h. Compute the dBm readings as described in
b. Disconnect the test leads.
c. Disconnect the power cord from the power
to SET LEVEL, algebraically add -20 dBm to
the computed reading. If the switch is set to
Section Ill. OPERATION UNDER UNUSUAL CONDITIONS
313. Operation in Arctic Climates
314. Operation in Tropical Climates
Subzero temperatures and climatic conditions
In tropical climates, electronic equipment may be
associated with cold weather may hamper the
installed in tents, huts or, when necessary, in un-
efficient operation of electronic equipment. In-
derground dugouts. When equipment is installed
below ground, and when it is set up in swamp
structions and precautions for operation under
such adverse conditions follow:
areas, danger of moisture damage is more acute
a. Keep the equipment warm and dry. If the
than normal in the tropics. Ventilation is usually
equipment is not kept in a heated enclosure, con-
very poor, and the high relative humidity causes
struct an insulated box for its protection.
b. Make certain the equipment has been
perature becomes lower than the ambient air. To
warmed up sufficiently before use. This may take
counteract this condition, place lighted electric
15 to 30 minutes, depending on the temperature of
bulbs under the equipment.
the surrounding air.
315. Operation in Desert Climates
c. When equipment which has been exposed to
the cold is brought into a warm room, it will sweat
The main problem with electronic equipment in
until it reaches room temperature. When the
desert areas is the large amount of sand and dust
equipment has reached room temperature, dry it
that lodges in the moving parts and mechanical
assemblies. Cleaning and servicing intervals shall
be shortened according to local conditions.