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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. 2. No. 7-8
'UBLISHED BY THE HEWLETT-PACKARD COMPANY, 395 PAGE MILL ROAD, PALO ALTO, CALIFORNIA MARCH-APRIL, 1951
Power Measurements from
10 to 12,400 Megacycles
A F HIGH frequencies, instruments for set-up for signal generator standardization is
measuring power have wide usefulness. shown in Figure 1 . The signal generator is
This usefulness is based on the fact that meas connected through a length of coaxial cable
urements of h-f power can be made with to a bolometer mount where the output
good accuracy and have more significance power from the generator is absorbed. With
than measurements of h-f voltage or current. present-day signal generators that have a
To provide more complete coverage in the source impedance reasonably well matched
-hp- line of power-measuring equipment, a to the line impedance, this measurement can
number of new devices have been added to be made on the basis of maximum available
the basic group of power-measuring instru power with an untuned bolometer mount. If
ments described in the May, 1950 issue1. The the source impedance is unknown and a
complete line now includes power-measur measurement of maximum available power
ing equipment for use over the range from 10 is desired, a stub tuner can be used to trans
to 12,400 me. form the load impedance to the conjugate of
Power measurements have many practical the generator impedance. If the measure
h-f applications. For example, in the labora ment is desired in terms of a "flat" load, a
tory it is often necessary to standardize the slotted section can be inserted into the trans
output power from signal generators. By use mission line and the load tuned so that no
of the power meter and suitable bolometer reflection occurs.
mounts, such standardization becomes a sim The basic range of power measurements
ple and straightforward process. A typical with the -hp- Model 430 power meter is from
less than 50 microwatts to 10 milli
watts, a very useful range for most
s i g n al g en era t o r ap p l i cat i o n s .
However, this range can be easily
extended upward for higher power
measurements. For example, lossy
type coaxial cables can be used as
attenuators at frequencies up to
the UHF region, where the losses
of standard cables may be high
enough for a given application.
In waveguide systems, powers in
the range from 1 to 2 watts can be
Figure using Set-up for standardizing signal generator output poirer using
attenuated to the range of the
new -hp- ?Model 476A broad-hand holometer nmnnt 'B. P. Hand, Direct Reading L'HF Power Measurements,
and neu Model -t HIB poner meter. Hewlett-Packard Journal. Vol. 1. o. <(. May, 1950.
P R I N T E D I N U . S . A . COPYRIGHT 195! H E WLETT - PAC K ARO CO.