Attenuation and delay equalizers
1
Attenuation and Delay Equalizers W. R. LUNDRY T HE ADJUSTABLE loss characteristics obtained in the A and equalizers are shown by the curves of Figure 1. These curves show the maximum adjustment range above and below a reference loss which is approxi- mately 40 decibels in each equalizer. Pairs of curves are identified by a number corresponding to the line-up fre- quency in kilocycles. The loss can be adjusted con- tinuously or in small steps to fall on curves intermediate to those shown. All intermediate curves are approxi- mately proportional to the limiting cases shown. The A and equalizers are complex assemblies of ad- justable 2-terminal networks. Loss adjustment is obtained by changing the value of control resistances. These may be wire-wound and connected to a rotary switch for manual adjustment or they may be thermistors subject to control by a pilot frequency regulator. In addition to its adjustable sections the A equalizer also contains a series of fixed loss sections which serve to equalize the accumulated fixed errors of 11 auxiliary repeaters. These are simple configurations of familiar equalizer types. In some cases they are associated with adjustable sections in order to reduce the over-all A equal- izer loss to tolerable values. Precise control of the electrical characteristics is required at each step of manufacture to insure meeting end-product limits of ±0.13 decibels. Capacitance tolerances of =±=0.5 per cent and resistance tolerances of =±=1 per cent are required frequently. Resonant circuits are adjusted to frequency tolerances of =±=0.5 per cent and sometimes as close as =±=0.2 per cent by using slug-tuned inductors. The equalizer has 15 adjustable loss characteristics shown at the top of Figure 1. All adjustments are made by dials having 20 uniform loss steps. In general, the loss characteristics of the equalizer tend to be narrower and hence, to require a more precise setting of the resonant frequency of coil-capacitor combi- nations. For example, one of the equalizer charac- teristics adjusts the loss over a band 200 kc wide centered 50 100 200 400 800 1200 1600 2000 2400 2800 3200 FREQUENCY IN KILOCYCLES PER SECOND Figure 1. Adjustable loss characteristics of A and equalizers at 3,030 kc where the resonant frequency must be adjusted to =±=6 kc or =±=0.2 per cent. Since equalizers are used less frequently in the circuit, wider end product limits are tolerable. The performance of the completed equalizer is checked by comparing its loss to that of a standard equalizer at the maximum and minimum settings of each of the 15 controls on a recording loss circuit. Limits of +0.25 decibels are set on these characteristics. The designs of delay equalizers for this system follow the potential analogue method. To fit the inherently unbalanced nature of the coaxial circuit, unbalanced bridged- sections are used to realize the design. A family of six delay equalizers and two building-out networks has been developed. The largest of these contains 52 all-pass sections; the smallest, 8 sections. Each of the 52 all-pass sections is assembled in its indi- vidual shield. Most of these contain two inductances and three capacitances arranged in conventional bridged- T configuration. The capacitances are manufactured to close tolerances, usually one-half per cent. The inductors contain threaded magnetic plugs which are used to adjust the inductance to resonate with the associated capacitors. The critical frequencies of the sections, corresponding to the resonant frequencies of the series and shunt arms, are adjusted to an accuracy of =±=0.5 kc. At 3,000 kc this corresponds to a frequency accuracy of 0.017 per cent, or, in terms of the adjustable element, an inductance accuracy of 0.008 per cent. The comparatively wide manufacturing variations en- countered in the dissipation factor of the inductors makes it necessary to provide means for adjusting each one individually. This is done by adding two resistances external to the unit assembly at the time the resonance frequency adjustments are made. Selected resistance values are used to hold the loss of each section within =±=0.03 decibel of its nominal value. The completed equalizers are tested for transmission loss and phase shift to insure a product uniformity of =±=0.1 decibel loss and =±=1 degree phase over the entire operating band. Input and output impedances of each network are required to have a reflection coefficient of less than five per cent against a 75-ohm resistance. These limits are extremely close. However, they are barely adequate to insure satisfactory delay equalization of present-day television circuits 1,000 miles long (for example, New York-Chicago). Such circuits use approximately 30 equalizers distributed along the line and the cumulative effect of such manufacturing deviations is large. Digest of paper 49-246, "Attenuation and Delay Equalizers for Coaxial Lines," recom- mended by the AIEE Communication Committee and approved by the AIEE Technical Program Committee for presentation at the AIEE Fall General Meeting, Cincinnati, Ohio, October 17-21, 1949. Scheduled for publication in AIEE Transactions, volume 68, 1949. W. R. Lundry is with the Bell Telephone Laboratories, Inc., Murray Hill, N. J. 216 Lundry—Attenuation and Delay Equalizers ELECTRICAL ENGINEERING
Transcript of Attenuation and delay equalizers
Attenuation and Delay Equalizers
W. R. L U N D R Y
TH E ADJUSTABLE loss characteristics obtained in the A and Β equalizers are shown by the curves of
Figure 1. These curves show the maximum adjustment range above and below a reference loss which is approximately 40 decibels in each equalizer. Pairs of curves are identified by a number corresponding to the line-up frequency in kilocycles. The loss can be adjusted continuously or in small steps to fall on curves intermediate to those shown. All intermediate curves are approximately proportional to the limiting cases shown.
T h e A and Β equalizers are complex assemblies of adjustable 2-terminal networks. Loss adjustment is obtained by changing the value of control resistances. These may be wire-wound and connected to a rotary switch for manual adjustment or they may be thermistors subject to control by a pilot frequency regulator.
In addition to its adjustable sections the A equalizer also contains a series of fixed loss sections which serve to equalize the accumulated fixed errors of 11 auxiliary repeaters. These are simple configurations of familiar equalizer types. In some cases they are associated with adjustable sections in order to reduce the over-all A equalizer loss to tolerable values.
Precise control of the electrical characteristics is required at each step of manufacture to insure meeting end-product limits of ±0 .13 decibels. Capacitance tolerances of =±=0.5 per cent and resistance tolerances of =±=1 per cent are required frequently. Resonant circuits are adjusted to frequency tolerances of =±=0.5 per cent and sometimes as close as =±=0.2 per cent by using slug-tuned inductors.
The Β equalizer has 15 adjustable loss characteristics shown at the top of Figure 1. All adjustments are made by dials having 20 uniform loss steps.
In general, the loss characteristics of the Β equalizer tend to be narrower and hence, to require a more precise setting of the resonant frequency of coil-capacitor combinations. For example, one of the Β equalizer characteristics adjusts the loss over a band 200 kc wide centered
50 100 200 400 800 1200 1600 2000 2400 2800 3200 FREQUENCY IN K I L O C Y C L E S P E R SECOND
F i g u r e 1. Adjus tab le loss characterist ics of A a n d Β equal izers
at 3,030 kc where the resonant frequency must be adjusted to =±=6 kc or =±=0.2 per cent.
Since Β equalizers are used less frequently in the circuit, wider end product limits are tolerable. The performance of the completed equalizer is checked by comparing its loss to that of a standard equalizer at the maximum and minimum settings of each of the 15 controls on a recording loss circuit. Limits of + 0 . 2 5 decibels are set on these characteristics.
The designs of delay equalizers for this system follow the potential analogue method. To fit the inherently unbalanced nature of the coaxial circuit, unbalanced br idged-Τ sections are used to realize the design.
A family of six delay equalizers and two building-out networks has been developed. The largest of these contains 52 all-pass sections; the smallest, 8 sections.
Each of the 52 all-pass sections is assembled in its individual shield. Most of these contain two inductances and three capacitances arranged in conventional bridged-T configuration. The capacitances are manufactured to close tolerances, usually one-half per cent. The inductors contain threaded magnetic plugs which are used to adjust the inductance to resonate with the associated capacitors.
The critical frequencies of the sections, corresponding to the resonant frequencies of the series and shunt arms, are adjusted to an accuracy of =±=0.5 kc. At 3,000 kc this corresponds to a frequency accuracy of 0.017 per cent, or, in terms of the adjustable element, an inductance accuracy of 0.008 per cent.
The comparatively wide manufacturing variations encountered in the dissipation factor of the inductors makes it necessary to provide means for adjusting each one individually. This is done by adding two resistances external to the unit assembly at the time the resonance frequency adjustments are made. Selected resistance values are used to hold the loss of each section within =±=0.03 decibel of its nominal value.
The completed equalizers are tested for transmission loss and phase shift to insure a product uniformity of =±=0.1 decibel loss and =±=1 degree phase over the entire operating band. Input and output impedances of each network are required to have a reflection coefficient of less than five per cent against a 75-ohm resistance.
These limits are extremely close. However, they are barely adequate to insure satisfactory delay equalization of present-day television circuits 1,000 miles long (for example, New York-Chicago). Such circuits use approximately 30 equalizers distributed along the line and the cumulative effect of such manufacturing deviations is large. Digest of paper 49-246 , "Attenuation and Delay Equalizers for Coaxial Lines," recommended by the AIEE Communication Committee and approved by the AIEE Technical Program Committee for presentation at the AIEE Fall General Meeting, Cincinnati, Ohio, October 17-21, 1949. Scheduled for publication in AIEE Transactions, volume 68, 1949. W. R. Lundry is with the Bell Telephone Laboratories, Inc., Murray Hill, N. J.
216 Lundry—Attenuation and Delay Equalizers ELECTRICAL ENGINEERING
![Types of Explosives accessories - Mining and … Tube NONEL Detonator [HMX] 3 mm 1 mm 10 ELECTRIC DETONATORS a) Instantaneous Elect Det b) “L” Series Millisecond Delay Det c) Half](https://static.fdocument.org/doc/165x107/5cdcfb8d88c993400f8d4d8d/types-of-explosives-accessories-mining-and-tube-nonel-detonator-hmx-3-mm-1-mm.jpg)
