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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
.ISHED CALIFORNIA THE HEWLETT-PACKARD COMPANY, 275 PAGE MILL ROAD, PALO ALTO, CALIFORNIA JUNE, 1955
The New -hp- 15-21 KMC 10 MW Signal Generator
THE NEW -hp- 15-21 kilomegacycle signal generators, a direct-reading frequency dial is
generator is designed as a general-purpose obtained by mechanically tracking the resona
instrument which will give engineers working tor plunger with repeller voltage. The fre
in the 1 5-2 1 kmc region the same conveniences quency range is covered by using parts of two
and accuracy that have led to the wide accep modes, and mode switching is performed auto
tance of the other -hp- microwave generators. matically by the repeller tracking mechanism.
To this end the generator provides at least 10 The klystron temperatures are kept at a low
milliwatts ( + 10 dbm) of max value by drawing air through the louvred por
imum output over its com tion of the front panel directly across the tube
plete frequency range, is di and resonator.
rect-reading in frequency to within 1%, has a R-f power from the klystron is fed to a sim
direct-reading, accurate 100 db output attenu ple uncalibrated attenuator. This attenuator
ator, and is provided with a flexible modulator serves as the power set control and permits the
which gives pulse, square-wave or f-m modu attenuator output to be standardized to the
lation. nominal maximum output value of 10 milli
A block diagram of the circuit arrangement watts (in practice, at least 20 milliwatts are
of the new generator is shown in Fig. 2. The usually obtainable). The power level at the at
oscillator uses a type V40B reflex klystron op tenuator output is then monitored by a temper
erating with an external waveguide resonator ature- and sensitivity-compensated thermistor
which is tuned by a non-contacting type plun bridge. The power sample for the bridge is
ger. The number of times the oscillator is tuned split from the main output by a specially-de
through its frequency range is thus essentially signed directional coupler of the -hp- multi-
independent of tube life. As in the other -hp- hole type1'2.
Following the directional coupler is the main
output attenuator which is of the rotary type3.
This type of attenuator has advantages in that
it is not sensitive to frequency in this range, has
an attenuation which is controlled by a mathe
matical law, is accurate, and is mechanically
practical to construct. Since the attenuation
range of a single attenuator is less than that de
sirable in a quality signal generator, however,
the attenuator used is formed from two rotary
1 E. F. Barnett and J. K. Huntoo, "A Precision Directional Coupler Using
Multi-Hole Coupling," Hewlett-Packard Journal, Volume 3, No. 7-8,
March-April, 1952.
- E. F. Barnett, "More About the -hp- Precision Directional Couplers,"
Hewlett-Packard Journal, Vol. 4, No. 5-6, January-February, 1953.
Fig. 1. New -hp- Model 628A Signal Generator operates
3 B. P. Hand, "A Precision Wave Guide Attenuator Which Obeys a
from 15 to 21 kmc, provides at least 10 milliwatts over Mathematical Law," Hewlett-Packard Journal, Vol. 6, No. 5, Jan
complete band. uary, 1955.
P R I N T E D I N U . S . A . C O P Y R I G H T 1 9 5 5 H E W L E T T - P A C K A R D C O .