Cable TV Equipment (Overview)
A head-end is intended for cable TV system arrangement. The head-end has a plug-in design. Modulators, receivers and channel amplifiers are parts of the head-end. It is recommended that home receivers for satellite channel receiving should be used.
The modulators are manufactured both for a fixed-tuned channel and for a tunable one. There are single- and double-sideband versions for both of the types. The side band is suppressed by 60 dB in single-sideband modulators. The frequency is assigned in a 62,5 kHz step, heterodyne oscillator instability amounts to 10-5. All the modulators have audio and video control available. The level of the output signal of all the modulators is 90 dB/µV. Modulators like the other modules of the head-end are equipped with the attenuator with a tuning depth of 20 dB. A signal-to-noise ratio of the modulators is not less than 55 dB.
Alongside with using of converters with IF conversion television receivers and modulators are used for decreasing of an intermodulation interference level. The receivers are tunable in the whole TV range. Operating signal strength is within a 70-100 dB/µV limit.
Channel amplifiers are intended for using in small networks. They are manufactured in two versions: with AGC and without AGC. Having AGC available the amplifiers maintain the output level with a ± 1 dB accuracy when the input signal is changed within a 60-100 dB/µV limit. The amplifiers without AGC have a gain of 30±3dB. The amplifier selectivity through a channel is 35 dB, the noise ratio is 4 dB.
The head-end may be supplied with FM stereo modulators for FM signal transmission in cable network which have a level of 90 dB/µV with a control depth of -20 dB, with a frequency output of 100...109,9 MHz and a frequency output tuning step of 0,1 MHz.
The modules are set on a chassis intended for 11positions. The module output signals merge in a loop way and get into a wide-band final amplifier. It is possible to insert output signal from another chassis to the second amplifier input for summation. The final amplifier is constructed according to the Push-Pull scheme. It provides an output level of 120 dB/µV according to DIN 45004. Output signal magnitude in real networks for 20 and 35 channels is 105 dB/µV and 100 dB/µV correspondently. The typical amplitude-frequency characteristic unevenness value in a 48-860 MHz band is ±0,5 dB. The final amplifier is equipped with a test outlet with the signal strength loss of -26dB.
There is no common control box in the head-end and every module is operated in off-line mode. Energizing is effected by a pip power supply operating under the line voltage of 170-270 V. The possibility of antenna amplifier energizing is provided. The temperature range of the head-end module operation is +5...+55 oС.
We produce equipment for reverse channel (tapping devices, low-pass filters, house and trunk amplifiers, etc.), optical equipment (optical transmitters and optical nodes, optical measuring devices, etc.) see the section "Optical Equipment", DVB-C, DVB-T digital equipment (see the section "Digital TV").