Leaky cable,or some one call leaky coaxial cable or leaky feeder cable is a kind of coaxial cable that with communication system consisting of a kind of cable run along tunnels which emits and receives radio waves. It functions as an extended antenna. This cable is “leaky” in that it has gaps or slots in its outer conductor to allow the radio signal to leak into or out of the cable along its whole length. Because of this leakage of signal, cable amplifiers are required to be inserted at regular intervals, often from 350 to 500 metres, in order to boost the signal back up to the acceptable levels. This signal is usually picked up by portable transceivers carried by personnel. Also,transmissions from the transceivers are picked up by the feeder and carried to carried to other parts of the tunnel systems, which allows two-way radio communication throughout the tunnel system.

Often, the leaky feeders are used in the mining industry,subway or tunnel acting as a method of wireless communication between miners. The system is used as a primary communication system which has a transceiver small enough to be comfortably worn on a miner throughout an entire shift.
Underground subway
Leaky feeder system is used for underground wireless communication in mass transit subway. E.g: for most of the China mainland metro or rail transport systems of Hong Kong, leaky feeders were incorporated in the specification of the capital project and installed during construction. This provides emergency services seamless wireless communication from the underground to the surface. Beijing Subway Metro uses a leaky feeder system for its internal communication network Connection.  An alternative of using leaky feeder in underground railways is to use Distributed Antenna System (DAS). A DAS system was deployed in some Shenzhen City Subway stations by Transit Wireless to provide WiFi and mobile phone and data coverage for customers.
Airport wireless
Leaky coaxial cable system can also be used to allow reception of on-board GSM and WiFi signals for passenger aircraft. Because the Leaky coaxial cable system require lower weight and space than the antenna systems. So,it saves space and fuel.
Infrastructure buildings
Leaky cable systems also often used in warehouse,hotel or other industrial area where it is hard to get WiFi signals by using normal access ways. Some installations have 50–75 meters of leaky cables connected to the antenna output of access points.

 

 

 

Since 2001, it has been produced for copper casting, rolling and electroplating processes

Baotou steel has short length, uneven copper layer, wire drawing is easy to break, and pollution rings

and other defects, suitable for large length, high strength, large environment, corrosion-resistant composite

In 2001, it was independently developed by a company in Shanghai

The cladding copper production line is obtained.

Wrap the integrated circuit and weld it into a tube at the wrapped interface by fire welding.

Special rolling, brushing and varnishing processes combine copper and copper into one

Since 2003, all sales have been formed.

Global sales, product quality level in line with the world. Its characteristic is the product

The coating layer is thin and evenly long, especially suitable for communication, electronics,

Wire for power transmission; the price is insufficient, and it is difficult to combine bimetals

technical difficulties.

 

 

At the same time, various other processes such as horizontal continuous casting also came into being. Horizontal continuous casting is the continuous casting of copper liquid directly on the steel wire, in the mold cool to form a copper cladding. There is an alloy layer on the copper-steel contact surface, the alloy layers have an effect on conductivity. It is suitable for the production of large cross-section, large length complex The thickness of the composite layer can be selected arbitrarily and the bonding performance is good.The disadvantage is that the uniformity of the thickness of the composite layer is relatively poor, and there is an eccentric core, which is not suitable for small-sized composite wire with high electrical performance requirements.

This stage is three kinds of electroplating method, cladding method and horizontal continuous casting method The technology occupies the market. Before the development of domestic cladding copper-clad steel, the domestic high-end market is imported copper-clad steel wire from

Copperweld Bimetallics, LLC. There are agents. However, in 2003, after the domestic cladding method was put into production, the price ratio of Copperweld Bimetallics, LLC was low and had the same quality and performance. At that time, Copperweld Bimetallics, LLC’s copper price of clad steel wire drops again and again, the conductivity is 40%, the diameter is Φ0. 25 mm

The price of copper-clad steel wire is 80,000/t, and the price of domestic cladding method is

60,000/t; when the price of Copperweld Bimetallics, LLC in the United States drops to 60,000/t, domestic package recovered down to 56,000/t. By 2005, agents were unable to sell and withdrawn from the Chinese market. In 2007, the copper clad of Copperweld Bimetallics, LLC in the United States Steel production declined, and a domestic company bought the former world’s largest copper-clad steel company, American Kopwei Bimetals Co., Ltd. But the company’s sales volume of the products in China is not large, and the domestic market is basically dominated by  three major domestic products. Process occupation, the main reason for analysis is cost.

The following are some discussion of the main production processes, product quality, production cost and the development of new products.

2 Main copper-clad steel processes at home and abroad

Domestic applications are more electroplating method, coating method and horizontal connection.

Cast copper clad steel process. The hot-rolled double copper strip is used more abroad.

method, cladding method and hot dip plating method. First introduce the key to various processes

The process characteristics are convenient for the comparison of product quality and performance later.

2.1 Electroplating process

The electroplating process is used for copper-clad steel wires with a conductivity below 30%.

the most. The process flow of producing copper-clad steel wire by electroplating is shown in Figure 1.

Figure 1 Process flow chart of copper-clad steel wire production by electroplating

It can be seen from Figure 1 that the process is mainly composed of three parts. First, the surface of the steel wire is treated, the oil is removed and the oxide layer is removed, and then copper or nickel is pre-plated.

Thicken the copper layer, clean it later, and add antioxidants or surface passivators.

The basic principle of electroplating copper-clad steel [4]: ​​The steel wire that has been pre-treated and pre-plated with nickel is immersed in the electroplating solution, and the steel wire (cathode) and the copper plate are immersed in the electroplating solution.

A certain voltage is applied to (anode). On the anode, the copper plate continuously loses electrons and forms free copper ions under the action of electrolysis

Dissociated in the electroplating solution: Cu－2e →Cu2+, on the cathode, under the action of electrolysis of the steel wire, the bivalent copper ions regain electrons and sink

Accumulated on the surface of the steel wire to form a copper-clad steel wire: Cu2+ + 2e →Cu，
Cu2++ →  e Cu+，Cu++ → e Cu，2H++2e →H2。

To plate copper ions on the surface of the steel wire, it is necessary to prevent the direct redox reaction between iron and copper ions. The direct redox reaction between steel and copper ions is the most basic problem to be solved by iron-based copper electroplating. This process can be expressed as: Fe +Cu2 → + Fe2+ + Cu;Fe2

The steel wire itself provides electrons and is converted into ferrous ions, which means the dissolution of the steel wire, which forms the so-called rotten wire. The replaced copper layer formed by this process does not involve electrodeposition, and the bond is very weak. To prevent possible dissolution of the steel wire, pre-plating must be used.

Mature pre-plating processes are cyanide plating, copper nickel plating and high phosphorus ratio pyrophosphate copper plating. Cyanide copper plating solution has good dispersibility and good coating

Dense, strong adhesion and other characteristics. However, it is difficult for domestic equipment to solve the environmental protection problem of cyanide, and other formulas are generally used. In subsequent wire drawing add for the electroplating of workers, it is better to use nickel plating as a pre-plating base. The main plating (thickening) copper can be acid sulfate copper plating or fluoboric acid.

Therefore, the electroplating process must improve the adhesion, compactness, continuity and stability of the copper layer in order to obtain high-quality Copper-clad steel wire, this is the difficulty of electroplating, and it is more difficult to increase the thickness of the coating layer in electroplating. The general wire diameter is only 2.5 mm or less conductivity is below 20%.

cladding process

The process of producing copper-clad billet wire by cladding welding method is mainly composed of raw material pretreatment, cladding welding and copper-steel bonding. The pretreatment of raw materials is mainly to thoroughly clean the copper strip and steel wire before cladding, to remove the oil stains and oxides on the surface, so as to ensure the good adhesion of the copper clad steel wire. Overlap soldering is where the copper tape enters the soldered

After setting, it is gradually formed, and the steel wire is covered in the process of forming the round tube, and then the two parts of the longitudinal seam of the copper tube that is constantly moving forward are welded by argon tungsten arc welding.

The edges are welded together to form a uniformly clad copper-clad steel wire billet. Copper-steel bonding through specially developed special processes and equipment, using special rolling

Pulling process, the copper and steel are bonded together to form a good bond between atoms. Production process of copper-clad steel double gold wire by clad welding method

see Figure 2

 

1. Classification of wires and cables

There are thousands of types of wire and cable products, which are used in all walks of life. There are two general uses for them, one is to transmit current and the other is to transmit signals. The main technical performance indicators for transmission current cables are conductor resistance and withstand voltage performance; the main technical performance indicators for transmission signal cables are transmission performance-characteristic impedance, attenuation and crosstalk. Of course, the transmission of signals mainly relies on electric current (electromagnetic waves) as the carrier. Now with the development of science and technology, light waves can be used as the carrier for transmission.

Generally speaking, cables can be divided into six categories:

1. Cables for electrical equipment

Connecting wires used for electrical equipment, with internal wiring or external wiring.

2. Power cable

Also known as power cable, used to transmit electric energy: it is often laid underground (urban electric power transmission).

3. Overhead wire (bare wire)

Also known as bare wire, it is used for special input of electric energy; it is often used for overhead laying, which has low cost.

4. Communication cable

Used to transmit electrical signals; often laid underground or overhead.

5. Enameled wire (winding wire)

Also known as winding wire, it is used in motor windings to convert electrical energy into mechanical energy.

6. Optical woven optical cable

It is used to transmit optical signals. Because of its low attenuation performance, it is often used as the backbone of long-distance communication.

Second, the meaning of wire and cable specifications and models

1. Model and name

RV－Copper core vinyl chloride insulated connecting cable (wire)

AVR－Tinned copper core polyethylene insulated flat connecting flexible cable (wire)

RVB－Copper core PVC flat connecting wire

RVS-copper core PVC stranded connecting wire

RVV－Copper core PVC insulated PVC sheathed round connecting flexible cable

ARVV－Tinned copper core PVC insulated PVC sheathed flat connecting flexible cable

RVVB－Copper core PVC insulated and sheathed flat connecting flexible cable

RV-105 copper core heat-resistant 105oC PVC insulated PVC insulated flexible connection cable

AF-205AFS-250AFP-250 silver-plated polychloroethylene fluoride plastic insulation, high temperature resistance -60oC~250oC connecting flexible wire

2. The meaning of specification notation

The specifications are expressed by the number of cores, nominal cross-section and voltage level

①Single-core branch cable specification representation: the number of cables in the same loop* (1*nominal section), 0.6/1KV, such as: 4*(1*185)+1*95 0.6/1KV

②The specification of multi-core stranded branch cable: the number of cables in the same loop * nominal cross section, 0.6/1KV, such as: 4**185+1*95 0.6/1KV

 

 

Wire and cable specification model description

Model	Name	use
BX（BLX） BXF（BLXF） BXR	Copper (aluminum) core rubber insulated wire Copper (aluminum) core neoprene rubber insulated wire Copper core rubber insulated cord	Suitable for electrical equipment and lighting devices with AC 500V and below or DC 1000V and below
BV（BLV） BVV（BLVV） BVVB（BLVVB） BVR BV-105	Copper (aluminum) core PVC insulated wire Copper (aluminum) core PVC insulated PVC sheathed round wire Copper (aluminum) core PVC insulated and sheathed flat wire Copper (aluminum) core PVC insulated cord Copper core heat-resistant 105°C PVC insulated cord	Suitable for all kinds of AC and DC electrical installations, electrical meters, instruments, telecommunications equipment, power and lighting circuits for fixed laying
RV RVB RVS RV-105 RXS RX	Copper core PVC insulated cord Copper core PVC insulated parallel cord Copper core PVC insulated stranded flexible wire Copper core heat-resistant 105°C PVC insulated flexible connecting wire Copper core rubber insulated cotton yarn braided twisted flexible wire Copper core rubber insulated cotton yarn braided round flexible wire	Suitable for the connection of various AC and DC electrical appliances, electrical instruments, household appliances, small electric tools, power and lighting devices
BBX BBLX	Copper core rubber insulated glass wire braided wire Aluminum core rubber insulated glass wire braided wire	Applicable voltages are 500V and 250V respectively, which are used for indoor and outdoor fixed installation or pipe laying

 

Note: B (B)-the first letter represents wiring, and the second letter represents glass fiber weaving.

V (V)-The first letter represents polyethylene (plastic) insulation, and the second letter represents polyethylene sheath.

L(L)——Aluminum, if there is no L, it means copper

F (F)-compound type

R-flexible cord

S-twisted pair

X-insulating rubber

Third, the basic structure of the cable

Generally, the most basic structure of a cable includes conductor, insulating layer and outer protective layer. Add another structure according to requirements, such as shielding layer, inner protective layer or armor layer, etc., and add some filling materials for the roundness of the cable. A conductor is a carrier for transmitting current or signals, and other structures are used for protection. There are three types of protection performance according to the needs of cable products. One is to protect the various units of the cable itself from mutual or reduce influence, such as withstand voltage, heat resistance, anti-loss caused by electromagnetic fields, and anti-signal interference of communication cables. The other type of protection is to protect the current in the conductor from affecting the outside, such as preventing current leakage and electromagnetic wave leakage, etc.; the last type of protection is to protect the outside from affecting the inside of the cable, such as compression resistance, tensile resistance, heat resistance, weather resistance, Flame-resistant, waterproof, anti-electromagnetic wave interference, etc.The following is a brief introduction to the structural units of the power cable.

1) Conductor (or conductive core): its function is to conduct current. There are solid core and stranded. The materials include copper, aluminum, silver, copper-clad steel, aluminum-clad steel, etc. The main ones are copper and aluminum. The conductivity of copper is much better than that of aluminum. The national standard requirements for the resistivity of copper conductors are not less than 0.017241Ω.mm2/m (at 20°C), and the resistivity of aluminum conductors is not less than 0.028264Ω.mm2/m (at 20°C).

2) Refractory layer:

Only fire-resistant cables have this structure. Its function is that the cable can withstand a certain period of time in a fire, giving people more time to use electricity when they escape. The material currently used is mainly mica tape. In a fire, the cable will burn quickly. Because the mica sheet of the mica tape is resistant to high temperature and has an insulating effect, it can protect the conductor from running for a certain period of time in a fire.

The following is a brief introduction to the structural units of the power cable.

1) Conductor (or conductive core): its function is to conduct current. There are solid core and stranded. The materials include copper, aluminum, silver, copper-clad steel, aluminum-clad steel, etc. The main ones are copper and aluminum. The conductivity of copper is much better than that of aluminum. The national standard requirements for the resistivity of copper conductors are not less than 0.017241Ω.mm2/m (at 20°C), and the resistivity of aluminum conductors is not less than 0.028264Ω.mm2/m (at 20°C).

2) Refractory layer:

Only fire-resistant cables have this structure. Its function is that the cable can withstand a certain period of time in a fire, giving people more time to use electricity when they escape. The material currently used is mainly mica tape. In a fire, the cable will burn quickly. Because the mica sheet of the mica tape is resistant to high temperature and has an insulating effect, it can protect the conductor from running for a certain period of time in a fire.

4) Shielding layer:

Outside the insulating layer and inside the outer protective layer, the role is to limit the electric field and electromagnetic interference. For different types of cables, the shielding materials are different, mainly: copper wire braiding, copper wire winding, aluminum wire (aluminum alloy wire) braiding, copper tape, aluminum foil, aluminum (steel) plastic tape, steel tape, etc. Longitudinal package and so on.

5) Filling layer:

The main function of the filling is to make the cable round and stable. The filling of some cables also plays a role in water blocking and fire resistance. The main materials are polypropylene rope, glass fiber rope, asbestos rope, rubber, etc. There are many types, but one of the main performance requirements is a non-hygroscopic material, which of course cannot conduct electricity.

6) Inner protective layer:

The function of the inner protective layer is to protect the insulated core from being damaged by the armor layer or the shielding layer. The inner protective layer has several forms such as squeezing, wrapping and vertical wrapping. For those with high requirements, the squeezed bag is used, and for those with low requirements, the wrapping or vertical bag is used. Nowadays, there are many kinds of materials used for wrapping. For example, the inner sheath of steel tape armor is wrapped with PVC tape, or polypropylene tape (very thin, made of particles on the surface to make up the thickness). of. Can it be used? The main problem is the market positioning of cable product quality. This is different from whether the silane cross-linked insulated core is distinguished by color or by color band. The properties are somewhat the same, but not all. The use of PVC tape and polypropylene tape for wrapping tape here has an impact on product quality. Whether the silane cross-linked insulated core is distinguished by color or by color band has little effect on product quality, mainly due to the needs of users.

7) Armour layer:

The role of the armor layer is to protect the cable from being damaged by external forces. The most common are steel tape armor and steel wire armor, as well as aluminum tape armor and stainless steel tape armor. The main function of steel tape armor is compression resistance, and the main function of steel wire armor is tension resistance. According to the size of the cable, the thickness of the steel strip used for armoring is different, which is stipulated in various cable standards.

8) Outer sheath:

The component that plays a protective role on the outermost layer of the cable.

There are three main types: plastic, rubber and metal. Among them, the most commonly used plastics are polyvinyl chloride plastics and polyethylene plastics, as well as flame-retardant, low-smoke and low-halogen type, and low-smoke and halogen-free type according to cable characteristics.

The above is the basic structure of general cables. Some types of cables have simpler structures, only conductors and insulation layers, and some cables do not have armor or shielding layers. Therefore, various types of cables are produced according to different structures and materials. There are thousands of types of wire and cable products, which are used in all walks of life. There are two general uses for them, one is to transmit current and the other is to transmit signals. The main technical performance indicators for transmission current cables are conductor resistance and withstand voltage performance; the main technical performance indicators for transmission signal cables are transmission performance-characteristic impedance, attenuation and crosstalk. Of course, the transmission of signals mainly relies on electric current (electromagnetic waves) as the carrier. Now with the development of science and technology, light waves can be used as the carrier for transmission.

 

Hello, every one. Welcome to Zhuhai hanqin cable co.,ltd   , in this article, we are going to discuss the performance of the leaky cables.

1 The mechanism of leaky cables

The purpose of a common coaxial cable is to transmit radio frequency energy from one end to the other, and it is desirable to have the largest horizontal shielding so that the signal cannot penetrate the cable to avoid the loss of radio frequency energy during transmission. However, the design purpose of a leaky cable is precisely to reduce the lateral shielding so that electromagnetic energy can partially penetrate from the cable to the outside of the cable. Of course, the electromagnetic energy outside the cable will also be induced into the cable.
Single-core wires or twisted pairs are leaky feeders, and coaxial cables or waveguides that allow leakage of outer conductors are also leaky feeders. However, the transmission attenuation of single-core wire or twisted-pair wire is too large for high frequency, and the size of the waveguide is large (<3GHz) and the cost is quite expensive. Therefore, the widely used leaky feeder is the coaxial leaky cable—— Its transmission attenuation, cost and installation are close to those of ordinary cables.

Leaky cables generally use thin copper as the outer conductor, and different forms of slots are cut on the outer conductor. According to different leakage mechanisms, leaky cables can be divided into two types: coupling type and radiating type.
The spacing of the slots on the outer conductor of the coupling leaky cable is much smaller than the working wavelength. The electromagnetic field is diffracted through the small hole to excite the external electromagnetic field of the outer conductor of the cable, so that there is current on the outer conductor, so there is electromagnetic radiation. The electromagnetic energy spreads around the cable in concentric circles. The cable with embossed and milled holes on the outer conductor is a typical coupling leaky cable.
The spacing of the slots on the outer conductor of the radiating leaky cable is equivalent to the wavelength (or half-wavelength), and the slot structure makes the signal superimpose in the same phase at the slot. Only a very precise slot structure and a specific narrow frequency band can produce in-phase superposition. Periodically changing slots on the outer conductor are typical radiating leaky cables.

Coupling leakage is the secondary effect of surface waves on the outer conductor of the leaky cable, while radiation leakage is caused by direct radiation from the slot on the outer conductor. Coupling cables are suitable for wide-spectrum transmission. The electromagnetic energy leaked has no directionality and decreases rapidly with the increase of distance. The radiating leaky cable is closely related to the operating frequency. The leaked electromagnetic energy has directivity. The same leaked energy can be relatively concentrated in the radiation direction, and will not decrease rapidly with the increase of the distance (for a specific frequency and a specified direction, the coupling The loss is relatively small).

Therefore, different types of leaky cables can be selected according to different applications. For example, the tunnel coverage of the private network can be the radiation type, and the indoor distribution system of the public network can be the coupling type. Generally speaking, leaky cables have two leakage modes: coupling and radiation. The so-called coupling type and radiation type mean that the leakage is mainly coupling or radiation.

2 Loss analysis

The material and physical structure of the inner and outer conductor, medium and sheath of the cable and its process determine the electrical and physical properties of the cable, and the slot structure on the outer conductor of the leaky cable (slot shape, slot size, arrangement density, arrangement Frame type) determines the different interaction modes of the electromagnetic energy in the cable and the external environment, which will affect almost all the electrical performance indicators of the cable.
The main electrical performance indicators of leaky cables include: frequency range, characteristic impedance, coupling loss, transmission attenuation, dynamic range of total loss, standing wave ratio, and transmission delay. The main physical performance indicators are: insulation resistance, dielectric strength (pressure resistance), flame-retardant and smoke toxicity properties, torsion resistance and bending properties, and airtightness.
As mentioned above, a leaky cable is similar to a combination of a transmission line and an antenna, and its purpose is to enhance the field strength coverage along the line. For wireless systems, the most important thing is the total loss index of the leaky cable (longitudinal transmission attenuation of the cable plus lateral coupling loss). It is the goal of system design to select the smallest system loss to maximize the service distance.
2.1 Transmission attenuation
The attenuation coefficient is an important indicator that describes the degree of electromagnetic energy loss transmitted inside the cable. There are two factors that cause the transmission attenuation of a coaxial cable: conductor loss and dielectric loss. For leaky cables, because part of the electromagnetic energy is radiated, there is still leakage loss. The attenuation coefficient of the leaky cable longitudinal transmission can be expressed by the following formula：

a = a1 ×+ a 2 × f+ a 3——-(1)

Among them, a =Attenuation coefficient for a given frequency （dB/100m）

a 1 =Conductor loss factor

a 2 =Dielectric loss factor

a 3 =Leakage loss factor

f =frequency （MHz）

Conductor loss and frequency relate to a 1 。a 1  depends on the impedance and the size of conductor.  Obviously, big cable’s conductor has lower loss. Because of the skin effect, the inner conductor of the thick cable can be made of aluminum and copper coated on the surface or a hollow copper tube can be used. For leaky cables, the conductivity of the outer conductor surface layer should also be as large as possible.

Dielectric loss has relations with frequency and a .

a 2 Determined by the relative dielectric constant and loss factor of the medium, foamed polyethylene (mesh In the past, the physical foaming method of injecting nitrogen was used, and the foaming degree can reach 80%.) When it is used as a dielectric material, its loss coefficient is the smallest. Leakage loss coefficient a 3 It depends on the slot structure of the cable, and will also be affected by the frequency and the surrounding environment of the cable.

2.2 Coupling loss

Coupling loss is a comprehensive index describing the radiation amount and receivable amount of a leaky cable. The coupling loss value is defined as the ratio (dB) of the signal in the cable to the signal received by the λ/2 dipole antenna at a specific distance (usually 2 meters) away from the cable.

Obviously, the smaller the coupling loss (the more leakage), the greater the transmission attenuation, but the slot structure can be selected to maximize the radiated energy and minimize the additional transmission attenuation due to leakage (the above-mentioned radiating leaky cable is an example). In the process of design or selection, the factors that can be controlled are: slot size, shape, frame format, and spacing.

For coupled leaky cables, the increase in frequency will reduce the coupling loss, so to a certain extent, it will compensate for the increased transmission attenuation due to the increase in frequency.

Since the influence is mutual, a similar method can also be used to analyze the coupling of the signal from the external antenna to the cable.

2.3 Total loss

The total loss of the leaky cable is the basis of the link design, which is defined as the sum of the cable transmission attenuation and the coupling loss. The total loss of the leaky cable shall not exceed the allowable system loss (transmitting power-receiving sensitivity). Taking the honeycomb system as an example, it may

The typical value of the acceptable system loss is 130dB, and the attenuation caused by the duplexer, shielding and other factors will be about 15dB. Therefore, considering the system margin, the total loss of the leaky cable should not exceed 105dB.

The above coupling loss is based on the premise that the antenna is 2 meters away from the leaky cable. Assuming that the antenna distance is 6 meters instead of 2 meters, the measured coupling loss will be about 5dB greater.

Figure 1 shows the total loss of two leaky cables with the same size but different leakage. The radiation of the leaky cable ② is greater than that of the leaky cable.

①, the transmission attenuation is therefore greater than ①. It can be seen that as the length increases, the total loss of the leaky cable ② with larger radiation will exceed that of the leaky cable ① and its dynamic change is relatively large.

 

Figure 1 Transmission attenuation + coupling loss = total loss of leaky cable

2.4 Dynamic range of total loss

The change in the loop loss between the mobile station and the base station caused by the change in the position of the mobile station relative to the leaky cable is quite large. When there are only base stations and mobile stations, fluctuations in total loss are not a problem, because both base stations and mobile stations have a large dynamic adaptation range: automatic gain control (AGC) can compensate for far-near effects and the damage caused by barriers and multipaths. Profit decline.

But once a repeater (especially an optical repeater) is introduced, the dynamic range of the uplink signal becomes a problem: if the signal level is too low, it may be overwhelmed by noise; if the signal is too strong, it will cause intermodulation in the waveband. Efforts can be made on the relay equipment side: such as using low-noise amplifiers to increase sensitivity; using frequency-selective repeaters to suppress intermodulation interference; or using feedforward technology in broadband repeaters to increase linearity.

However, it is most beneficial to make the total loss curve of the leaky cable flat. Two factors affect the dynamic range of the total loss: the gradual increase in transmission attenuation; the jitter of the coupling loss (Rayleigh fading).

1. Reducing the dynamic range The dynamic range of the loss is very important to the system design, and each transceiver has its requirements. Along the leaky cable, the total loss (transmission attenuation plus coupling loss) increases. Therefore, the coupling loss is gradually reduced along the direction
2. To compensate for the longitudinal transmission attenuation, the usable length of the cable will increase significantly. According to the principle of gradual decrease in coupling loss (increase in relative leakage), the segmented design of the slot structure (for example, the slot is changed from sparse to dense) can reduce the total loss dynamic range of the entire leaky cable-that is, the actual field strength distribution along the line is more The conventional leaky cable will be more uniform, as shown in Figure 2.

 

Coupling loss and “reception probability

Due to the superposition of different phases, the sampling value of the coupling loss varies along the longitudinal direction of the cable with jitter, as shown in Figure 3.Commonly referred to as coupling

Figure 2 It is necessary to reduce the coupling loss in sections to reduce the dynamic range to standardize the expression of this jitter. It is also conducive to the reliable design of the system. We get a specific coupling loss value based on the reception probability.

 

Figure 3 The receiving probability curve derived from the jitter of the coupling loss

 

Commonly used are 50% and 95% probability values. 50% reception probability value-50% of the measured data of coupling loss is better (less than) this value.

95% reception probability value-95% of the measured data of coupling loss is better (less than) this value.

Using the 95% reception probability value as the coupling loss value is closer to actual needs, and the determined loss value is greater than the 50% reception probability loss value. Similarly, a 5% probability value can be calculated. The 95% probability loss value and the difference between the 95% probability and 5% probability loss value (a measure of jitter) are a basis for link design.

50 Ohm Leaky Cable

2.5  Factors to be considered when designing the system margin

 

From base station to mobile station                                                                    From mobile station base station

——————————————————————————————————————————————————-

Base station transmitter output power                                                                Mobile station transmitter output power

Jumper cable loss                                                                                              Mobile station antenna loss or gain

Power splitter loss                                                                                             Coupling loss

Leaky cable transmission attenuation                                                                Required system margin

Repeater gain                                                                                                      Leaky cable transmission attenuation

Coupling loss                                                                                                       Repeater gain

Required system margin                                                                                   Power splitter loss

Mobile station antenna loss or gain                                                               Jumper cable loss

Mobile station receiving sensitivity                                                               Base station receiving sensitivity

3 environment affection

 

Installation location

The installation position of the leaky cable has a great influence on the coupling loss. During installation, the cable axis should be kept at a distance of more than 20cm from the wall, and the cable should be kept at least 1 meter away from the corner of the wall.

Metal bracket

Non-metallic brackets should be used to install leaky cables. Metal brackets with periodic outlets will affect the standing waves in the leaky cables to a certain extent.

Oil & Water

The dust and oil stains containing salt or metal particles accumulated on the sheath of the leaky cable are potential loss factors and can increase the transmission attenuation.

Opening direction of radiating leaky cable

There are a series of openings on the outer conductor of the leaky cable. In order to obtain the smallest coupling loss and the smallest field strength fluctuation, the direction of the opening of the leaky cable must be directed toward the mobile device.

Welcome to Zhuhai hanqin cable co.,ltd.   In this article, we are going to discuss the performance principle of the Leaky Cable.

 

Leaky cable is short for leaky coaxial cable, which is a special coaxial cable. Leaky coaxial cable is a special coaxial cable that is slotted at a certain interval and in different forms in the longitudinal direction of the outer conductor of the coaxial cable. The purpose of slotting is to make the electrical signal energy radiate from the cable slot to achieve the purpose of spreading and receiving external radio waves. This radio wave is open, like a hole for radio waves to enter and exit. An open “door”.

The energy of the signal is guided by the length of the leaking cable, and the effective area is limited by the environmental influence of the inner and outer surrounding areas of the cable, so that the signal can continue to enter the mobile communication unit. a) Bamboo knot shape b) Spiral shape c) Lotus shape d) Foam shape like a conventional coaxial cable. The signal transmission depends on the voltage difference between the inner core wire and the outer sheath.

For example, if we intentionally cut a slot to block the current, the current has to surround the slot, which causes the current magnetic field inside the cable to change, so that the slot acts like a coupling antenna and generates radiation. The energy is emitted from the electronic waveguide. Was leaked. This rule applies to the construction of slot antennas in waveguides, so the measurement and description of a slot or a pair of slots often make the method of mapping leaky coaxial cables: leaky coaxial cables can be considered for making coupled antennas. Leaky cables can be divided into two types: radiation type and coupling type according to the different ways of slotting.

a) Radiating leaky cable b) Coupled leaking cable The grooves in the outer conductor of the radiating leaky cable are periodically arranged, and the form of radiation is similar to the radiation of a series of magnetic dipoles distributed along the axis of the leaking cable, and All slots conform to the principle of phase superposition, and the most typical interval is half the wavelength of the transmitted electromagnetic wave signal. The outer conductor of the coupled leaky cable generally has periodic slots of parallel lines. The periodic slot couples out a part of the energy transmitted inside the cable, forming a surface wave outside the cable, and the propagation law of the surface wave is The transmission guided waves in the body are basically the same. The coupled leaky cable rain spoke.

The difference between the leaky cable is that the gap between the grooves of the leaky coupling cable is much smaller than the working wavelength. Therefore, in this coupling mode, the electromagnetic field excites the electromagnetic field through the groove diffraction. Due to the skin effect, the induced resonant charge is only along the shielding. With the movement of the outer surface of the conductor, the leaky cable is like a long display dipole antenna radiating electromagnetic waves, and the coupled leaky cable is like an electronic antenna. The entire leaky cable can be seen as a collection of a series of small antennas.

a Anatomical diagram of TE10 mode electromagnetic wave transmitted by a coupling leaky cable (solid lines are power lines, and dashed lines are magnetic lines of force)  b The structure of the electromagnetic field coupling leaky cable at the slot is shown in the figure, and figure b shows the distortion of the electromagnetic field at the slot. , Produced an electric dipole. So how is the electric dipole produced?

In order to explain this problem, according to the principle of electromagnetic conversion, first analyze the situation of the conductor with the same size as the slotted hole. It is assumed that the charge makes a reciprocating simple harmonic motion along the conductor, and a pair of electric dipoles produces a direction in a reciprocating cycle. In this way, the dipole makes a simple harmonic motion with the center of the conductor as the center point in the conductor, and finally forms a series of concentric electric field lines that radiate outwards. According to the principle of reciprocity, on one side of the conductor The conductors with slots of the same area will produce opposite concentric magnetic lines of force, which is the exchange of electric field and magnetic field. The electromagnetic waves coupled at close distances have a concentric structure, but if they are transmitted over long distances, they will be greatly affected by factors such as the surrounding environment and diffraction, and the electromagnetic waves will be interfered when they are emitted outwards, and the space transmission distance will be very limited.

The function of the feeder and the jumper are both connection and transmission models, and both serve as the medium for connecting devices or equipment. The main difference between the two is the connection distance and softness.

Feeder: RF cable that transmits RF signals. A coaxial radio frequency cable generally used for the transmission of radio frequency signals from BTS equipment to antenna feeders. The length is longer, the general dimension is larger, and the 7/8″ feeder has lower loss as the backbone.

Jumper: a short cable (or optical fiber) connecting equipment and devices. The essence is not much different from the feeder, but because the bending radius is small and soft, it is used to connect the feeder and the antenna, and the feeder and the BTS equipment, and the length is shorter. Another kind of jumper is fiber jumper, which connects optical transmission equipment in short distance. The optical fiber jumper reduces the loss to a minimum because the optical fiber has almost zero loss in transmission through photoelectric conversion.

Jumpers are divided into indoor jumpers and outdoor jumpers. The connection line from the arrester to the combiner (or surf) is called an indoor jumper, which is generally 3 meters long. Commonly used connectors are 7/16DIN type and N type. There are straight and elbows. Outdoor jumper is also called small antenna antenna. It is the connection line connecting the 7/8 “main feeder and the lower interface of the antenna. Normally it is 2 meters (this is the case produced by Datang Telecom). Indoor jumpers are generally soft jumpers. Therefore, in the case of sufficient resources, do not exchange indoor jumpers for outdoor jumpers. In addition, indoor and outdoor jumpers are divided into pressure heads and manual heads.

The feeder is a very long line from the arrester to the outdoor jumper. The main function of the feeder is to efficiently send the radio frequency carrier signal output by the transmitter to the antenna. On the one hand, the attenuation of the feeder is required to be small, and on the other hand, its impedance should match the output impedance of the transmitter and the input impedance of the antenna as much as possible. .

(1) Antennas mainly include the following types:

A) Suction cup antenna: moderate price, convenient installation, moderate gain, suitable for installation on moving vehicles, or adsorption on metal objects. Generally, the gain is 2.6dB, 5dB, etc.

B) Anti-theft antenna: moderate price, easy to install, with the same gain as a suction cup antenna. When installed outside of a metal box, it cannot be removed from the outside of the box, so it is called an anti-theft antenna.

C) Low-gain omnidirectional antenna: The gain is 3.5dB, and the installation requires a fixed bracket, which is suitable for long-distance multi-point transmission.

d) High-gain omnidirectional antenna: The gain is 8.5dB, and the installation requires a fixed bracket, which is suitable for long-distance multi-point transmission.

E) Directional antenna: The gain is very high, 12dB, and the installation requires a fixed bracket, which is suitable for long-distance transmission in a fixed direction

(2) Feeders mainly include the following types:

A) The feeder loss of 50-3 (impedance 50Ω, cross-section 3) is 0.2dB/m.

B) The feeder loss of 50-7 (impedance 50Ω, cross section 7) is 0.1dB/m

C) The feeder loss of 50-9 (impedance 50Ω, cross section 9) is 0.07dB/m.

The feeder is an important equipment connecting the radio and the antenna

The TPA module is a TD-SCDMA power amplifier unit. The TPA is located between the RFU and the smart antenna subsystem. It consists of a low-noise amplifier in the upstream direction and a multi-carrier power amplifier transceiver switch in the downstream direction, as well as a control and alarm unit. It provides the necessary radio frequency power to the antenna and pre-amplifies the received signal to a certain level to meet the further processing requirements of the RFU. Because the TPA module is directly close to the antenna array, it can reduce cable loss and improve the effective transmit power of the antenna and the system’s receiving sensitivity.

A TDB09A TPA box contains 4 antenna power amplifiers. Two TPA boxes form an 8-channel antenna power amplifier, which is connected to an 8-period smart antenna.

 

Hello, welcome to Zhuhai Hanqin Cable Co.,Ltd.   In this article, we will talk about the difference between coaxial cable and twist pair network cables.

First, COAXIAL CABLE:
Coaxial cable has the advantages of being cheaper and easier to lay
(Relative to optical fiber), so, generally in a small-scale monitoring system, by
Because the transmission distance is very short, the use of coaxial cables to directly transmit the monitoring image does not cause much damage to the image quality, which can meet the actual requirements.
However, according to the analysis of the characteristics of the coaxial cable itself, when the signal is transmitted in the coaxial cable, its attenuation is related to the transmission distance and the signal itself.
The frequency is related. Generally speaking, the higher the signal frequency, the greater the attenuation. The bandwidth of the video signal is very large, reaching
6MHz, and the color part of the image is modulated at the high end of the frequency. In this way, when the video signal is transmitted in the coaxial cable, not only the overall signal amplitude is attenuated, but also the attenuation of each frequency component varies greatly, especially the color part attenuation is the largest. Therefore, coaxial cables are only suitable for short-distance transmission of image signals. When the transmission distance reaches about 200 m, the image quality will be significantly reduced, especially the color becomes dim and there is a sense of distortion.

In engineering practice, in order to extend the transmission distance, a coaxial amplifier is used. The coaxial amplifier can amplify the video signal to a certain extent, and also
Different frequency components can be compensated in different sizes through equalization adjustment, so that the distortion of the video signal output by the receiving end is as small as possible. But
Yes, coaxial amplifiers cannot be cascaded indefinitely. Generally, coaxial amplifiers can only be cascaded up to 2  to 3  in a point-to-point system.
Otherwise, the video transmission quality cannot be guaranteed, and it is difficult to adjust. Therefore, when using a coaxial cable in a monitoring system, in order to ensure a better
Generally, the transmission distance is limited to about four or five hundred meters.
In addition, coaxial cables still have some shortcomings in the transmission of image signals in the monitoring system:
1) The coaxial cable itself is greatly affected by climate change, and the image quality is affected to a certain extent;
2) The coaxial cable is relatively thick, which is not convenient for wiring in intensive monitoring applications;
3) Generally, coaxial cables can only transmit video signals. If the system needs to transmit control data, audio and other signals at the same time, additional wiring is required.
Line
4) Coaxial cable has limited anti-interference ability and cannot be used in strong interference environment;
5) The coaxial amplifier also has the disadvantage of difficulty in adjustment.

Second, Twisted pair
Twisted pair has been used for a long time. Telephone transmission uses twisted pair, which is used in many industrial control systems and places with greater interference and long distances.
Twisted-pair cables are used in remote transmission, and the local area network that we widely use today also uses twisted-pair cables. The reason why twisted pair is so widely used,
It is because it has many advantages such as strong anti-interference ability, long transmission distance, easy wiring, and low price. Since the twisted pair signal also exists
Larger attenuation, so when the transmission distance is long, the frequency of the signal cannot be too high, while high-speed signals such as Ethernet can only be restricted to
Within 100m. For video signals, the bandwidth reaches 6MHz. If it is directly transmitted in a twisted pair cable, it will also attenuate greatly. Therefore, the video signal is
To achieve long-distance transmission on a twisted wire, amplification and compensation must be carried out. The twisted pair video transmission equipment is to complete this function. Plus a pair of twisted pairs
After the line video transceiver equipment, the image can be transmitted from 1  to 2km. Twisted-pair and twisted-pair video transmission equipment are very cheap, not only without
Increasing the cost of the system, on the contrary, when the distance increases, its cost is much lower than that of the coaxial cable. Therefore, in the monitoring system, the twisted pair is used for transmission.
Transmission has obvious advantages: 1) Long transmission distance and high transmission quality. Due to the advanced processing technology used in the twisted pair transceiver, it perfectly compensates for the attenuation of the twisted pair to the video signal amplitude and the attenuation difference between different frequencies, and maintains the brightness and color of the original image and the real-time performance. When the transmission distance reaches 1km or more, the image signal is basically without distortion. If the relay mode is adopted, the transmission distance will be longer.
2) Convenient wiring and high cable utilization. A pair of ordinary telephone lines can be used to transmit video signals. In addition, the extensively paved buildings in the building
Any pair of unshielded twisted pair cables of category 5  can transmit one video signal without additional wiring. Even if it is re-wiring, category 5 cables are better than the same
Shaft cable is easy. In addition, a category 5 cable has 4 pairs of twisted-pair wires. If a pair of wires is used to transmit the video signal, the other pairs of wires can also be used.
To transmit audio signals, control signals, power supply or other signals, improve cable utilization, and avoid separate wiring of various signals
The trouble here has reduced the project cost.
3) Strong anti-interference ability. Twisted-pair cable can effectively suppress common mode interference. Even in a strong interference environment, twisted-pair cable can transmit excellent image signals.
Number. Moreover, the use of several pairs of twisted pairs in a cable to transmit different signals respectively without interference with each other.

4) High reliability and easy to use. Use twisted pair cables to transmit video signals, and a dedicated transmitter must be connected at the front end, and a dedicated transmitter must be connected at the control center.
Receiver. This kind of twisted pair transmission equipment is cheap and easy to use. It does not require professional knowledge and does not require much operation.
Installation, long-term stable work.

5) The price is cheap and it is convenient to obtain materials. Because it uses the general 5  unshielded cable or general telephone line that is widely used at present, it is easy to purchase.
And the price is also very cheap, which brings great convenience to engineering applications.