The type C system was first installed about 1925 and has been very extensively used. It incorporates the most desirable features of the systems just considered. Like the type A system, the carrier is suppressed, and hence the effect of line attenuation is minimized. Like the type B, different frequencies are used for transmitting and receiving, an
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d filters, instead of carrier-frequency hybrid coils, are used to separate the talking and the receiving signals. The original type C carrier telephone system was extensively modified about 1938 to take advantage of developments in communication. Original Type C Carrier Telephone System. 30 The schematic diagram of the original type C carrier is shown in Fig. 20. To explain the operation of this system, assume that a person whose telephone is connected to channel 1 at the left is speaking to a person whose telephone is connected to channel 1 at the right. The incoming speech signals pass through the voice-frequency hybrid coil, and to the modulator at the top. This is a balanced modulator (page 421) that eliminates the carrier but produces both sidebands. The band filter selects one sideband and rejects the other. The selected sideband passes down to the common wires leading to the transmitting amplifier, where all the incoming signals to be transmitted are amplified to the proper level for impressing on the line. The amplified signals from the three channels pass through the high-pass filter and hence to the line. Each of the three modulators is fed with a different carrier frequency, and hence each of the three sidebands that are transmitted simultaneously is at a different frequency as Fig. 18 shows. Figure 20. Schematic diagram of original type C carrier telephone system, and of carrier and voice-frequency equipment at...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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