The structure of radio frequency cables is diversified and can be classified in different ways.
1. Cable structure classification
1) coaxial radio frequency cable
Coaxial RF cable is the most common structural mode. When the inner and outer conductors are in a concentric position, the electromagnetic energy is limited to the medium propagation between the inner and outer conductors, so it has significant advantages, that is, less weakening, high shielding performance, use frequency bandwidth and performance stability. Usually used to transfer RF energy from 500 kHz to 18KHz.
At present, there are two types of common RF coaxial cables: 50Ω and 75Ω RF coaxial cables. The characteristic impedance 75Ω RF coaxial cable is usually used in CATV network, so it is called COTV cable, and the transmission bandwidth is up to 1GHz. The current CATV cable is currently being transferred to 750MHz.
2) Symmetrical RF cable
The symmetrical RF cable track has an open electromagnetic field, and due to the high frequency of the radiated electromagnetic energy, the attenuation is increased, and the shielding is poor, and the influence of atmospheric conditions is usually rarely used. Symmetrical RF cables are mainly used for low radio frequency or symmetrical feeding.
3) spiral radio frequency cable
The conductor in a coaxial or symmetrical cable can sometimes be a spiral coil to increase the inductance of the cable, thereby increasing the wave impedance and transmission time of the cable. The former is a high-resistance cable, and the latter is used for a delay cable. If the spiral coils have different winding densities in the length direction, the cable can be varistorized.
2. Classification of Insulation Forms
1)physical insulated cables
All physical high-frequency dielectrics are filled between the inner and outer conductors of this kind of cable, and most flexible coaxial radio frequency cables use this form of insulation.
2)air insulated cable
In the cable insulation, except for a part of the solid medium that supports the inner and outer conductors, the rest is basically air. The structural feature of one conductor to another without passing through the mi
Electricians who want to conduct dielectric loss tests on power transformers, relays, capacitors, arresters, etc. need to use an anti-interference dielectric loss tester. As a relatively conventional high-voltage power test equipment, this equipment has high voltage levels and reliable accuracy. And other advantages, but there are still many problems that need to be paid attention to in the process of use, so what are the problems that should be paid attention to when using the anti-interference dielectric loss tester?
1. Ground the instrument reliably to ensure that the shell of the instrument is at ground potential.
2. For positive wiring: insert the high-voltage cable plug into the HV socket of the instrument, clamp the black alligator clip at one end to the high-end lead of the tested product, and hang the red alligator clip in the air. Insert the Cx low-voltage cable into the Cx socket, the red clip at the other end clamps the low end or the end screen of the test sample, and the black clip is suspended or connected to the shielding device.
3. When reverse wiring: insert the high-voltage cable plug into the HV socket of the instrument, clamp the red alligator clip at one end to the high-end lead of the tested product, and hang the black clip in the air or connect to the shielding device. The Cx socket is not used.
4. Comply with the requirements of "Safety Work Regulations for High Voltage Tests".
5. The high-pressure test must be attended by more than two staff members, with one operating and one supervising.
6. After the wiring is completed, one person is responsible for the inspection.
7. After the test, turn off the power switch. It is strictly forbidden to disassemble or assemble the high-voltage cable with power on!
8. If the instrument is abnormal, turn off the power switch and wait for about one minute to check again.
9. After the measurement is completed, the power switch must be turned off, and the wires will be removed after waiting for about one minute.
The BNC wire can be tested for its resistance, voltage, leakage current, open/short circuit and other parameters through the wire testing machine.
1. Baseband coaxial cable
The coaxial cable uses hard copper wire as the core and is covered with a layer of insulating material. This layer of insulating material is surrounded by a densely woven mesh conductor, and the mesh is covered with a layer of protective material. There are two widely used coaxial cables. One is a 50-ohm cable, which is used for digital transmission, and because it is mostly used for baseband transmission, it is also called a baseband coaxial cable; the other is a 75-ohm cable, which is used for analog transmission, which is the broadband coaxial cable to be discussed in the next section.
This structure of coaxial cable makes it have high bandwidth and excellent noise suppression characteristics. The bandwidth of a coaxial cable depends on the cable length. A 1km cable can reach a data transfer rate of 1Gb/s~2Gb/s. Longer cables can also be used, but the transmission rate should be reduced or intermediate amplifiers should be used. At present, coaxial cables are largely replaced by optical fibers, but they are still widely used in cable television and some local area networks.
2. Broadband coaxial cable
A coaxial cable system that uses a limited TV cable for analog signal transmission is called a broadband coaxial cable. The term "broadband" comes from the telephone industry and refers to a frequency band wider than 4kHz. However, in computer networks, "broadband cable" refers to any cable network that uses analog signals for transmission.
Because the broadband network uses standard cable television technology, the usable frequency band is as high as 300MHz (often to 450MHz); due to the use of analog signals, an electronic device needs to be placed at the interface to convert the bit stream entering the network into an analog signal, and Convert the signal output from the network into a bit stream.
Broadband systems are divided into multiple channels, and TV broadcasting usually occupies 6MHz channels. Each channel can be used for analog TV, CD quality sound (1.4Mb/s) or 3Mb/s digi
1. Video signal interface
Introduction of surveillance video cable types:
According to the material, there are SYV and SYWV. The physical material structure of the insulation layer is different. SYV is a solid polyethylene cable, and SYWV is a high-physical foam cable. The transmission performance of the physical foam cable is better than that of polyethylene.
S--coaxial cable Y--polyethylene V--polyvinyl chloride W--stabilized polyethylene
According to the impedance, it can be divided into SYV 50-XX SYV 75-XX SYV-100 XX XX represents the outer diameter of the insulating layer.
1. Composite video signal: the general connector is BNC, RCA (lotus head)
75 represents resistance, and the following 3 and 5 represent its insulation outer diameter (3mm/5mm).
S---coaxial radio frequency cable in SYV, Y---polyethylene, V---polyvinyl chloride.
SYV75-3 transmission works well within 200 meters.
SYV75-5 transmission is better within 500 meters.
2.S-terminal (or Y/C)
Its scientific name is "two-component video interface", commonly known as S-terminal, and the transmission distance is short 15 meters.
The S-Video connection specification is a specification developed by the Japanese. S refers to "SEPARATE (separation)", which separates the brightness and chroma to output, avoiding the mutual interference of brightness and chroma when the mixed video signal is output. The S interface is actually a five-core interface, consisting of two visual brightness signals, two video chrominance signals, and one common shielded ground wire, consisting of five core wires.
Compared with the AV interface, since it no longer carries out Y/C mixed transmission, there is no need for bright color separation and decoding, and the use of independent transmission channels largely avoids the signal crosstalk in the video equipment. The image is distorted, which greatly improves the clarity of the image. However, S-Video still has to mix two color difference signals (Cr Cb) into a chrominance signal C, transmit it and then decode it into Cb and Cr in the display device for processing, which will still cause some signal loss. Distortion (this kind of distortion is very sma