Satellite TV room-to-room reception

The method of watching different satellite TV programs in different rooms is not very complicated, but it is quite professional. Let's start with "Satellite TV Watching in Different Rooms" in the 49th issue of "Electronic News" last year, page 3.

First, judging from the several circuit diagrams in the article, the equipment connection is too complicated. Since there are many devices and most of them are passive devices, the insertion loss is large, which reduces the level of the satellite TV downlink signal, which is not very strong. Moreover, the signal flow of this line is unknown, so it is easy to cause the failure of receiving programs. When the satellite TV downlink signal cannot be received, two satellite TV signal amplifiers are added. It is estimated that the output level of the first amplifier is much higher than the threshold level of the second amplifier, which causes this type of low-noise and high-sensitivity amplifier to be blocked and cut off, and thus cannot amplify the signal. The following solutions can achieve the purpose of satellite TV reception in different rooms.

1. Take two antennas receiving 105.5°E~[176.5°E satellite TV signals as an example, and its wiring diagram is shown in Figure 1. In Figure 1, after the two antennas are led down with 75-5 TV cables, a satellite TV two-power distributor is used as a mixer to mix the signals received by the two antennas. The method is: use the input and output ports of the two-power distributor in reverse, use its output port as the input port of the two-way signal, and use the input port as the output port of the mixed signal. In essence, the satellite TV power distributor is based on the same principle as the cable TV distributor, but the upper and lower limit frequencies are much higher than those of the cable TV distributor, so it is completely possible to use it as a broadband mixer for satellite TV signals. This avoids using a satellite TV switcher to switch signals. The mixed satellite TV signal is then connected to a satellite TV two-power distributor, one way enters room one, and the other way enters room two, and each is connected to a satellite TV receiver. The satellite TV signal received by the satellite TV receiver is demodulated and converted into a video signal V and an audio signal A output, and this AV signal then enters the AV input port of the TV for the TV to watch. For the cable TV signal source, a cable TV splitter is used to split the cable TV signal into two paths, entering room one and room two respectively, and plugged into the TV RF signal inlet for receiving cable TV signals. In this way, satellite TV receivers can be controlled in different rooms to watch different satellite TV programs and cable TV programs.

The disadvantages of this are: 1. Two satellite TV power splitters are used, and the insertion loss is large. If the satellite TV signal is weak, a satellite TV antenna amplifier must be installed. The antenna amplifiers with dotted lines in the two places in the figure should be installed according to the strength of the signal, and the location of the installation also depends on the situation (on the road section with weak signals). 2. When receiving two signals, the TV needs to perform AV or RF conversion, which is troublesome. 3. It is possible that the downlink signals received by the two satellite TV antennas enter the two power splitters for mixing, and the two signals with adjacent downlink frequencies will have a little interference, but this phenomenon is generally rare.

2. Taking a satellite TV antenna as an example, the method of receiving TV using radio frequency signals RF is introduced.

As shown in Figure 2, the downlink signal received by the satellite TV antenna is divided into two paths by a two-way power splitter, and then enters room one and room two respectively and then connects to the satellite TV receiver. Generally speaking, satellite TV receivers are equipped with RF output ports. In this way, the RF signal output by the satellite TV receiver is mixed with the cable TV signal divided by the two-way splitter, and then mixed by a cable TV two-way splitter as a mixer, and then enters the RF input port of the TV for viewing. Since the RF frequency of a general satellite TV receiver is after 22CH, it is impossible to interfere with the cable TV signal, and the bandwidth of the cable TV two-way splitter is 5MHz-1000MHz, which is completely capable of mixing the two signals. If this method is used to demodulate the cable TV signal and there is interference, the AV output signal of the satellite TV signal received by the satellite TV receiver after demodulation can be RF modulated according to the method in Figure 3. The modulator should be selected as the adjacent frequency agile frequency type, and the vacant channel frequency of the cable TV should be selected for output. After the mixed cable TV signal is reversed by the two-way splitter, it is input into the RF input port of the TV for viewing. If the adjacent frequency agile frequency modulator is too expensive, a video recorder with tuning, which is rarely used nowadays, can be used as a modulator. The RF output of the video recorder has two adjustable channels, which can effectively avoid mutual interference.

When connecting, the TV cable should be as short as possible to reduce the cable's signal loss. The cable should be of good quality to ensure 75Ω matching. Passive components should also have 75Ω matching impedance, and the reflection loss should be greater than 16dB to reduce the standing wave intensity formed by the reflected wave to avoid ghosting.