OPERATING PROCEDURES

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-

u p . Typical sources of spurious radiation are induction or dielectric heating units,

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.

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