Section II. GENERAL DESCRIPTION

GENERAL DESCRIPTION

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.

AN/URM-145