GENERAL RADIO COMPANY 874-GAL Operating Instructions Manual

Adjustable attenuator

Advertisement

OPERATING INSTRUCTIONS
TYPE 874-GAL
ADJUSTABLE
The Type 874-GAL Adjustable Attenuator is of the wave-guide-
below-cutoff
type operating in the TE
The waveguide is excited by a coaxial trankmission line, as shown in Fig-
ure 1, and the output voltage is induced in a loop mounted on a sliding
plunger.
One end of the loop is terminated in a 50-ohm resistor and the
other is connected to the output cable. This arrangement makes the output
impedance of the attenuator approximately 50 ohms.
varied by rotating the barrel which moves the plunger and loop along the
tube.
The barrel is calibrated in relative attenuation in dB. The attenu-
ators can be adjusted from the stop at the minimum attenuation position,
which occurs at about -9dB on the calibrated scale, to the stop at the max-
imum attenuation end of the range, which occurs at about 140 dB on the
scale.
Each revolution of the barrel changes the attenuation 20 dB. In
most applications the maximum usable attenuation is limited by leakage
from various parts of the driving circuit and not by the range of the atten-
uator. In this type of variable attenuator, as the attenuation is varied the
phase at the output connection is essentially constant with respect to the
input signal phase.
The method of coupling to the coaxial line permits the attenuator
to be used as a standard calibrated attenuator or as a device to couple a
small amount of energy from a high-level circuit for monitoring or meas-
uring purposes without introducing a large discontinuity in the main line.
The Type 874-GAL Coaxial Attenuator employs the new Type 874—BL
Locking Coaxial Connectors.
ably with the standard GR874~Connectors.
locking connector, a firm mechanical coupling of the two is achieved
when the coupling shell is engaged. The shielding is also improved sig-
nificantly, and, in general, the leakage is reduced by at least 50 dB.
The "quick-disconnect" feature of the standard GR874 Coaxial Con-
nectors is retained in the locking
gaged. However, in this case the shielding is not as effective.
ATTENUATOR

DESCRIPTION

1 ~ mode (inductive coupling).
These connectors can be used interchange-
When mated with another
if the coupling shell is not en-
type
The attenuation is

Advertisement

Table of Contents
loading
Need help?

Need help?

Do you have a question about the 874-GAL and is the answer not in the manual?

Questions and answers

Subscribe to Our Youtube Channel

Summary of Contents for GENERAL RADIO COMPANY 874-GAL

  • Page 1 The Type 874-GAL Coaxial Attenuator employs the new Type 874—BL Locking Coaxial Connectors. These connectors can be used interchange- ably with the standard GR874~Connectors.
  • Page 2 ERRORS In all waveguide attenuators, the excitation of modes other than the desired one distorts the theoretical attenuation characteristic, particularly at low attenuation levels. In the Type 874-GAL Attenuator, the TM mode (capacitive coupling) is the most serious offender. This mode...
  • Page 3 Figure 4 of the VSWR seen looking back into the out- put connector for a typical unit. The tolerance on the dc resistance of the 50-ohm resistor is ± 10%. TYPE 874-GAL ADJUSTABLE ATTENUATOR 3...
  • Page 4 Readings of the detector output and attenuator setting are first made without the circuit under test connected. The circuit is then inserted and the Type 874-GAL Adjustable Attenuator is readjusted to give the same detector indication. The attenuation of the unknown circuit is then the difference in the attenuator readings.
  • Page 5 NORMAL from reading. For opposite connection, add REVERSED ~ correction. it~t. ATTENUATOR READING A, dB 874 0.12 Figure 2. Correction chart for use with Type 874-GAL Adjustable Attenuator when exciting line is terminated in its characteristic impedance. TYPE 874-GAL ADJUSTABLE ATTENUATOR...
  • Page 6 K) a Indicated AttenuatIon ~‘ 0.00~ 1000 2000 3000 4000 FREQUENCY, MHz 874 G-lO Figure 4. VSWR seen looking back into output con- nector of a typical Type 874-GAL Ad. > justable Attenuator. FREQUENCY. GHz 874 G.8 6 GENERAL RADIO...
  • Page 7 Figure 5. Block diagram of a simple signal generator using the adjustable attenuator and other GR874 Coaxial Elements. TYPE 874—D2OL —D5OL TEST 874 G-14A Figure 6. Block diagram of setup for measuring the attenuation of a network. TYPE 874-GAL ADJUSTABLE ATTENUATOR 7...
  • Page 8 FREQUENCY. 8 74.0.13 Figure VSWR introduced in a flat line by the insertion of a Type 874-GAL Adjustable Attenuator. SPECIFICATIONS A waveguide-below-cutoff type, useful as a calibrated attenuator or as a sampling device. Calibrated in decibels, on a micrometer-type scale.

Table of Contents