The AN/URM-145 RF Voltmeter is a sensitive instrument
for the measurement of voltages of 300 microvolt to 3 Volts
spanning a frequency range of 20 kilocycles to 600 megacycles.
In addition to conveniently measuring voltage levels in a di-
versity of RF circuits, the instrument has application for many
associated tests. Such measurements include: the frequency
response of both active and passive networks, i.e., amplifiers
and filters; VSWR and return loss on transmission lines and
attendant systems; attenuation and insertion loss of RF attenu-
ators; and high frequency parameters of transistors. With true
RMS response below 0.03 Volt, wide band noise can be measured, and
using suitable null networks measurement of the harmonic distor-
tion of RF waveforms can be performed without the attendant errors
of average type meters.
The instrument is also useful as an RF null detector for
bridge measurements and analogous techniques when a sensitivity
in the order of 200 microvolt will suffice.
Supplied with each instrument is a general purpose RF
Probe, 50 ohm Adapter, and probe Tip. The adapter is fitted with
a BNC coaxial connector and provides a 50 ohm termination with a
low VSWR up to 600 megacycles. The Probe Tip is useful for di-
rect measurement to approximately 250 megacycles, however, a short
wire should be substituted for the ground lead when using above
100 Mc to minimize the effects of ground lead inductance. Above
250 megacycles, the probe may be used directly without the tip
but the connecting leads must be extremely short to avoid resonant
effects. Normally the RF Probe is used with the
Adapter in a
coaxial system for accurate measurements above 100 Mc.