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Video Monitoring


Modulators - the junction of CCTV and SMATV/MATV systems
Modulators are used for conversion and distribution of audio and video signals from different sources (CCTV cameras, SAT receivers etc.) via the existing antenna installation. The RF signal coming from the modulator can be received by any TV receiver connected to the installation. CCTV applications allow to monitor several locations in one or several TV channels. Of course, the images from CCTV cameras can be recorded on VCRs or DVRs.
There are 2 types of modulators used in the TV/CCTV technology:
  • DSB - AM (dual side band, amplitude modulation)
  • VSB - AM (vestigial side band, amplitude modulation
They differ in the spectrum, which means the width of the frequency band. VSB-AM modulation is used by terrestrial TV transmitters and higher-class modulators, for example those in the headend stations of cable TV. VSB-AM modulator can work without an extra space between channels (e.g. on 50, 51, 52, 53, 54, 55, etc. channels), which allows the maximum channel capacity. However, it costs several times more than DSB-AM modulator.
DSB-AM modulation is used in simple modulators built in sat receivers, VCRs etc. DSB-AM modulators, due to broader spectrum, require one-channel spacing (they can work e.g. on 50, 52, 54, 56 ... channels). It should be remembered that the free channel has to be the one below the working channel.
The spectrum of DSB - AM and VSB - AM signals
Generally, there are two groups of modulators on the market: simple and inexpensive modulators for home users and professional and semi-professional devices.
Examples from the first group are Signal Digital Classic R95176 (sound subcarrier: 6.5 MHz), R95175 (sound subcarrier 5.5 MHz - PAL-G). The output channel can be set within whole UHF band (ch. 21-69). They are equipped with AC/DC adapter and RF cable. Typical output level: 70 dBuV.
The group of semi-professional modulators includes, among others, MT-21P R871721 (Terra).
MT-30A R871731 MT-30B R871732 MT-30C R871733 (Terra) belong to the professional group of modulators and use VSB-AM modulation.
Most modulators work on 21-69 channels (sometimes on channels 6-12 and S9-S16), usually in B/G standard, although there is no problem with accessing D/K versions. The input connectors are usually in chinch or mini-DIN form. Typical output level is 80 dBuV and there is almost always possibility of adjusting this parameter.
If there is a need to add a few modulators to RF installation, and for the reason of too many channels already distributed it is not possible (e.g. only one free channel is available), the images from several CCTV cameras have to be put into a divider and then the output signal should modulate the one free channel.
Without such a problem, very useful in practice are 2, 4, 6 - channel modulators ( R95165, R951664, R95167), which allow distribution of images from several cameras using one AC/DC adapter.
Antenna UHF Preamplifier AA-101 ALCAD
MIXPOL MDP-6 - channels S1-S38, 1-12, 21-69
Audio-video demodulator Mixpol R87203 is used to change high frequency TV signal to baseband audio-video signal. This device is sold together with remote control which is used for configuration i.e. programming and storing selection of input channels. The demodulators can be used together with additional modulators for multiplying transmission possibilities of existing coaxial cable in order to transmit signals from several cameras over the same cable (especially useful when there is no possibility to lay down additional cables).
TV Modulator TERRA MT-41

Caution. In the above scheme, the images from individual cameras are available on different channels - the monitor can display only the image from a selected camera (after setting adequate channel on the demodulator). If we want (e.g. for further processing) to make all channels available at he same time, we need to use the same number of demodulators as modulators.
TV Modulator TERRA MT-41TV Modulator TERRA MT-41Broadband TV Combiner - ST 1-69Subscriber Terminal Outlet: Signal RTV2-Way TV/FM Splitter R-2 SignalSubscriber Pass-through Outlet: Alcad BM-700 (FM&DAB/TV, 15dB, flush)Subscriber Pass-through Outlet: Alcad BM-500 (FM&DAB/TV, 10dB, flush)
Example of using modulators and demodulators for transmission of signals through antenna installation - from surveillance cameras to digital recording card

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