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HEWLETT-PACKARD
JOURNAL
T E C H N I C A L I N F O R M A T I O N F R O M T H E - h p - L A B O R A T O R I E S
BUSHED CALIFORNIA THE HEWLETT-PACKARD COMPANY, 395 PAGE MILL ROAD, PALO ALTO, CALIFORNIA
Direct Reading UHF Power
Measurements
A T HIGH frequencies as at low the power In use, the instrument operates as easily and
-/^-flowing in a system is a frequently- quickly as a vacuum-tube voltmeter.
sought factor. In fact, at high frequencies The high-frequency power to be measured
power assumes extreme significance, for nei is absorbed in a bolometer element. Since
ther voltage nor current as such can be read such elements customarily have an imped
ily measured. ance of 200 ohms and are operated with 50-
Figure 1 shows a direct-reading high-fre ohm transmission systems, an intermediate
quency power meter that measures the out device is required to transform the bolo
put power from signal generators, oscillators, meter impedance down to the line imped
and similar equipment. In effect, this power ance so that maximum power transfer can
meter is an automatic version of the common occur. Such a device is the tunable bolometer
bolometer substitution bridge; but, because mount shown in Figure 2.
its operation is automatic, measurements can The frequency at which high-frequency
be made quickly