TM 11-6625-524-14-4
Turn the POWER selector switch to ON. With the RF probe and its termination con-
nected to the de-energized signal source, slowly rotate the SET REF adjust con-
trol until a SET REF indication occurs. This adjustment should be made carefully,
especially on the lower, more sensitive ranges.
The voltmeter is ready for use. If the level of measurement shows less than 30% of
full scale, rotate the RANGE selector switch to a range position where the meter
reading indicates between 30% and 100% of full scale. To obtain readings in dBm,
add dBm meter reading (red scale on meter dial) to the dBm setting of the RANGE
selector switch.
CAUTION
Damage to the probe's diode cartridge may result if the input exceeds 42V
P-P, 15V RMS or 400V DC.
When measuring low level RF voltages, always take precautions to avoid the possibil-
ity of erroneous readings resulting from hum, noise or stray rf pickup. Although
all low freqeuncy hum and noise is attenuated at the input by 60dB, it is still
possible for high level unwanted signals to get through and cause errors. The best
t e s t for this condition is to reduce the test signal to zero level and note whether
the voltmeter continues to read some spurious signal level. In some cases, extra
shielding may be necessary around the probe connections to reduce stray field pick-
d i a t h e r m y machines, l o c a l radio transmitters, grid dip meters, and amplifiers with
parasitic oscillations.
Operation of the voltmeter in strong 60 Hertz (Hz) magnetic fields, such as those
surrounding unshielded power transformers, should be avoided. The magnetic field
induces small 60Hz currents in the amplifier section of the voltmeter which, due
to the extremely high gain at this frequency, appear as an indication on the meter.
