Choosing high quality coaxial cable, relevant equipment, normative construction, installation quality, timely and rational maintenance and repair are the basic conditions to  achieve transmitting high quality signals. We will discuss hereinafter the cautions about choosing, installing and maintaining coaxial cable for the relevant working people to refer to.

(1)Definitely don’t use counterfeit and shoddy coaxial cable because counterfeit and shoddy products are often  jerry-built  and shoddy when they were produced. So those products are inferior in quality and their technical characteristic with no guarantee, such as the materials of internal and external conductor and insulating medium have inferior quality and inaccurate parameter. Consequently it results in too many deviations of characteristic impedance、too big attenuation constant、bad frequency characteristic、temperature characteristic and inferior shielding properties, etc.

(2)Do not misuse characteristic impedance. Characteristic impedance is an important technical parameter of coaxial cable. The frequently-used technical parameters are 75 and 50 Ω,etc. There will be many disadvantages if the impedance is mismatched when being used such as the SNR(Signal to Noise Ratio) of transmitted signal will decline、the image will generate ghosting or produce thick and thin cobwebbing interference、the system frequency characteristic will deteriorate and the data error rate in data transmission system will increase, etc.

(3)Prevent mixing internal conductor with external conductor when being connected. Coaxial cable is a kind of transmission line with special construction. Its internal and external conductor have their own specific syntagmatic relations and effects. Circuit connection also has its specific connecting way. The internal and external conductor can not be optionally interchanged. Otherwise, normal signal transmission will be affected thus leading to dissatisfactory results .

(4)Improve the installation quality of cable terminal and joint. Do not neglect the connection quality of external conductor, when connecting coaxial cable terminal with terminal box and amplifier, etc. If  the connections are loose or disjointed,the signal level will be lowered greatly. In the cable TV system, there is usually an obvious horizontal black fringe in the middle of the TV screen and interference fringes in the vertical direction which move towards the left slowly. The system is also susceptible to interferences from the nearby power and radio frequency. When the contact resistance between external conductor and  contact joint turns too large (for example, external conductor joint oxidation and contact joint rustiness) the reverse attenuation characteristics would turn up, on the contrary ,attenuation of low frequency band would be stronger. The nonstandard assembly of coaxial cable between cable joint and connection point may cause characteristic impedance of joint changes greatly. Consequently reflection shows up and standing wave interference forms.

(5)Prevent coaxial cables from interferences when paralleled with power lines. Electric transmission line, power transformer, electromotor and industrial electrical installation, all kinds of household appliances are all strong electromagnetic pollution source. when wiring coaxial cables, it can neither parallel with power lines nor pass through. You’d better keep it far from electric appliances and circuits, thus the above mentioned interferences can be avoided to some extent and damages caused by electric power line leakage ,overheat and fire can also be prevented. 

(6)Enhance moisture proof and waterproof measures. In the open area and places with water, watertight caisson must be installed in the amplifier and branch distributor, etc. Coaxial cable joint close to end should be fabricated waterproof bending(winding path with downward arc) in case that water flows into joints or other circuits. Cable ends(joints) should be painted sealant. The moisture and vapour come into cables mainly by cable heads and sheathes. Therefore, inspection and maintenance of sheathes can not be neglected. Once the sheath breakage is discovered, take the bandage treatment timely.

(7)Do not reserve too many circuits. Signal attenuation in cables increases along with the increase of cable length. Usually attenuation increases 2 dB every 10m cable. Therefore, the shorter distance of the cable is expected and too many circuits can not be reserved when it is wired. But, some people rolled the reserved cable into a small dish and tie it up with wires. Consequently, the signal attenuation has increased and the system frequency characteristics have be changed, causing the performance degradation of signal high band which reflects on the reception of cable television and bad reception of UHF frequency band.

(8)Strictly forbid using the sharp objects to penetrate into cables for the signals. Some people penetrate into cables with pin 、sewing needle or small nails for stealing television signals, causing stable or unstable short circuit phenomenon between internal cable conductor and external conductor, causing great signal attenuation in the coaxial-cable circuit, influencing adjacent branch circuit and outward leakage of cable television signals. If rainwater or humidity invades cables by the pin hole, impacts, the losses would be greater.

Do not neglect the effects from high temperature. According to temperature characteristic of coaxial cable, when the environmental temperature rises, cable metal(internal and external conductor) losses and dielectric losses would increase. The cable decrement approximately increases 0.2% every l0C. Therefore, keep the coaxial cable away from high temperature heat source and environment while it is wired. When the temperature rises too much, the signal quality may be lowered and system stability would be destroyed.

Prevent mechanical damage. Coaxial cable is composed of the internal and external conductor which is concentric and mutually isolate and the internal and external conductor have the same axis. The physical structure decides a series of particular characteristics of coaxial cable .If the external force factors make the mechanical damage of coaxial cable, it is equal to say that the physical structure has be destroyed. Inevitably the electric parameters would be changed thus worsening the main features and the signal quality. In order to prevent mechanical damages of coaxial cable, the following points must be noted in project, construction and use：

① Strictly prohibit folding the coaxial cable into right angle when it is installed. Cable should be made circular arc in the corner. Turning radius shall not be five times less than outside diameter of cable.

② When the cable is installed outside, metal products are strictly prohibited to be used in cable fixed-caliper .The plastic nail for fixing the coaxial cable should be used and the plastic nail type must match with outside diameter of cable. It is not proper to be too large or small.

③ Make sure the safety of coaxial cable during construction. Pay attention not to smash, press, strike and prick.

④ Coaxial cable has limited mechanical strength. It can not be pulled strongly during the installation. In long distance installation ,the pulleys should be used to reduce the turning traction and the talcum powder should be put in pipeline to reduce the friction force from passing through cables 

⑤ When coaxial cables are installed on metopes and cylinders of corridor indoor or outdoor ,the PVC pipes should be used. If the coaxial cables are installed under the road, it can not be directly installed or protected by plastic pipes, but the galvanized tubes should be used.