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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
Vol. 9, No. 12
UBLISHED BY THE HEWLETT-PACKARD COMPANY, 275 PAGE MILL ROAD, PALO ALTO, CALIFORNIA AUGUST, 1958
An Automatic DC To X-Band Power Meter
For The Medium Power Range
HO measure high-frequency power in the Such a direct approach is achieved by a
range above the low milliwatt region new power meter that automatically mea
where direct bolometric methods reach a sures average power in the range from 10
limit, it has been usual practice to retain the milliwatts to 10 watts. The instrument is
basic bolometric method but to reduce the useful to at least 12 kilomegacycles and is
power actually measured by a known also capable of use down to dc if desired.
amount with attenuators and directional It can be used to measure any of the com
couplers. Although this approach provides mon forms of power such as ordinary ampli
useful information, a direct method is funda tude-modulated, pulsed ac, pulsed video,
mentally more desirable, since it would and dc. In distinction to methods where the
avoid the inconvenience of cascading several rf load is built into a special external mount,
components into a measuring setup and the new instrument contains an internal 50-
would also avoid the errors that additional ohm load which acts as the rf termination
components introduce into the measure and is provided with a type N coaxial con
ment. nector on the panel.
itm
TEMPERATURE )
SAUCE - COMPARISON
INPUT TEMPERATURE
SAUCE
-COMPARISON
LOAD
INPUT
LOAD METER
PUHP--
HEAT EXCHANCER
Fig. 1. New -hp- Model 434A Calorimetric Power Fig. 2. Basic circuit and oil stream arrangement of
Meter measures powers between a few milliwatts and Power Meter. Parallel-flow heat exchanger is located
10 watts at frequencies from dc to 12.4 kilomegacycles. physically close to load resistors to bring oil streams
Self-balancing type circuitry makes operation auto entering the two load-gauge regions to same tempera
matic and gives reading in less than 5 seconds. In ture. Arrangement also includes heat radiators (not
strument is provided with 50-ohm coaxial input. shown) down-stream from gauge resistors to dissipate
heat transferred from load resistors.
P R I N T E D I N U . S . A . C O P Y R I G H T 1 9 5 8 H E W L E T T - P A C K A R D C O .