How to find the best test cable among many options? Time Microwave Systems introduces you to an ideal choice for production testing and laboratory applications - the SilverLine test cable. The following sections describe the mechanical and electrical performance of cable and cable assemblies and how to choose your ideal test cable. In May 2004, the test engineers of American Times Microwave Systems made the following overview of the requirements for 50 ohm test cables: 1. Loss: One foot cable "0.09db/ft@1Ghz (excluding SMA and N-type connector) 2. Minimum bending radius: 0.75'' (1.5''bend diameter) 3. Excellent flexibility (good bending resistance) 4. 25,000 times 180 degree bending life 5. Good voltage standing wave ratio 6. Maximum operating frequency: 4GHz 7. High shielding rate 8. low cost Next, the customer might ask: "I don't need something that is too hard to get because I want to use them right away." However, they don't realize that some of the above requirements conflict with each other, in different areas of use. Apply different frequencies. Manufacturers must therefore strive to manufacture high-performance cables to help us identify which are practical and low-cost cables. After understanding the mechanical and RF performance, it is more helpful to help us choose the cable that best suits the application. The above will be a good start for our next discussion. With the development of various production technologies that can reduce attenuation without increasing the diameter, cable producers tell us that the lower the loss, the better the cable. Maybe this is not necessarily true, but we should be aware that some applications do need to achieve the level of loss that is difficult to achieve with flexible RG coaxial cables. In addition, to eliminate demand problems, many customers seeking high-quality test cables began to consider low losses as a necessity. Cable attenuation increases with increasing frequency, but the larger the diameter, the smaller the attenuation. The attenuation also decreases as the propagation rate (Vp) increases. Many flexible RG cables use solid polytetrafluoroethylene as a dielectric. With a propagation rate of approximately 70% (that is, a signal propagation rate equivalent to 70% in vacuum), solid Teflon media can make cables more robust and relatively low cost. We need to increase the joint loss to achieve balance, and try to keep the cost low with RG coaxial cable, only RG393-like cable can meet the customer's need for attenuation. As a result, some problems immediately became apparent. First of all, the cable of this size is very hard. Secondly, in the case of continuous bending, the bending radius will be limited to 10 times the outer diameter. Depending on the structure of the braid, the operating frequency and performance requirements, the minimum bend radius can be occasionally reduced to 5 times the outer diameter. In addition to this, the tape is permanently changed (stretched, wound) and the performance is changed. The 3.9 inch (equivalent to 7.8 inch diameter) has far exceeded the maximum limit set by the customer. Second, RG393 is not suitable for SMA type connectors. It complicates the installation process and can create unacceptable return loss. Finally, the properties of RG make it impossible to achieve the best shielding performance, so the supplier reduces the weaving angle (that is, it uses less braided wire). The less the braided wire, the stronger the flexibility, but the bending life will be shorter. Because the braid is easier to move or loose. Excessive research on RG cable specifications has led us to neglect other requirements. In summary, increasing the cable diameter may not be an acceptable solution to achieve the desired level of attenuation. Another way to save costs is to change the center conductor and or the outer layer structure. Customizing a solid center conductor will increase the loss by 10-15%, depending on the frequency. However, many single-core center conductors are copper-clad steel silver-plated structures, which are the best choice for non-flexible cables. Looking back at the flexibility requirements mentioned above, we need high-end copper-plated center conductors. A typical way is to replace the solid steel center conductor with a harder copper. The bending life and flexibility of some chain conductors will be redefined without affecting the increase in attenuation efficiency. Most common RG cables use one to two layers of silver-plated copper wire to braid the outer conductor. When exploring the improvement of the outer conductor, the manufacturer found the answer from the semi-steel copper sheathed cable. However, for the center conductor, the semi-rigidity is as low as the loss of solid polyethylene. Cable manufacturers are continually trying to reach their flexible cables with new braided structures and production methods. One common strategy to improve overall performance, including attenuation, is to supplement the single wrap with a 50% covered helicoid as an inner shield. While providing a more RF-friendly interface, the spiral face adds additional cable shielding. However, this structure also has its drawbacks. The RF capability will diminish faster as it bends. Usually a third flat braid is placed at the lower end of the spiral belt to help solve this problem. In contrast to media applications, the flat braid has a smooth surface like a spiral strip and is more flexible. In addition, the flat and spiral braid structure increases the attenuation to 10% depending on the frequency. In summary, although the three-layer braided cable is relatively rigid, it provides greater attenuation, shielding effectiveness, and longer bending life. However, by looking at the strength and angle of the braid and the strict control procedures, it is found that such cables also transmit higher frequencies. Under the condition of working frequency and minimum bending radius, the RF performance can be maintained when the bending degree is greater than that of the RG cable. The most effective way to reduce attenuation is not only to improve the braid and the center conductor, but also to change its center structure. Stretched polytetrafluoroethylene, expanded polytetrafluoroethylene, floral polytetrafluoroethylene, and expanded polyethylene are all methods used by manufacturers to increase the percentage of air in the medium, thereby reducing its dielectric constant. More air usually means a more flexible center conductor for more flexibility. In order to maintain proper impedance, a larger center conductor is needed to reduce impedance and lower losses. It is not difficult to find a low-loss cable with 90% or higher Vp. Such cables tend to have lower attenuation and sometimes even smaller and more flexible than the more expensive solid Teflon. It seems that low-loss cables are a suitable choice to meet the above requirements, however, there are also deficiencies. Low-loss products are often not suitable for use with finished connectors. Only connectors designed for such cables can be selected, so that the production cycle is extended and the cost is increased. Low-loss center conductors may be more prone to moisture, contaminated with flux and detergent, and will not be easily peeled off like a solid center pin. These problems can complicate installation and increase costs. This softer center structure makes it difficult to achieve high performance at higher frequencies. For example, the use of corrugated center conductors on the tape is too tight, resulting in higher return loss. If the center conductor is very soft, the braid components will move closer to each other, resulting in unstable RF performance, especially in terms of phase or electrical length. Moreover, the center conductor will deviate from the center position and change the impedance. Finally, low-loss cables are more susceptible to damage from external physical stress or other bending forces. The higher the Vp value, the more susceptible these problems are to deterioration. It seems that low-loss cables have too many problems to consider, but in fact some problems are often overlooked. The LMR, T-FLEX, SF, and SFT series of Time Microwave Systems are the best examples of high-performance cables with improved low-loss or braid structure, which not only minimizes loss, but also provides optimum flexibility and high frequency performance. Obviously, a low loss cable may need to meet or at least achieve a target loss value while still meeting the minimum bend radius/flexibility requirement. In order to meet the customer's price and delivery goals, we started with the catalog of LMR UltraFlex products from the era microwave system, which uses polyethylene media technology. Due to their wide range of applications in the telecommunications and wireless fields, expanded polyethylene cables and many connectors are everywhere and are very inexpensive. Vp at 80-87% of expanded polyethylene is also very inexpensive. The UltraFlex series offers superior bending moments compared to standard LMR or conventional expanded polyethylene cables. A 0.200'' diameter cable calculates a frequency loss of 0.12db, which is very close to customer demand. This gives us the perfect solution. Another product we are focusing on is TImes SFT316 with multiple center conductors. This is a 0.120" diameter, 76% rate wrapped PTFE cable. The softer Teflon medium is more suitable for flexibility and bending life requirements, and is closer to the bending radius requirement, but the loss value can reach 0.18db. The LMR is a double shielded cable product, while the SFT is a high shielded three layer cable. Each uses a different central structure. It can be seen that achieving all the requirements in one product is not as simple as the customer expects. The other properties of the test cable also make it an excellent cable product. Let's try to choose the right size connector for this cable. One way is to compare the cable center conductor diameter to the connector center pin diameter. Components of similar size make better matching at the connector, thereby optimizing return loss. Typically, the joints of the cable assemblies are most susceptible to breakage, so the tension mitigation system needs to provide a smooth transition from a rigid joint connection location to the cable. If the tension mitigation system cannot fix the joint connection part or can not function as a lever force point, it will not function properly and the joint will fall off prematurely. If possible, the method of solder joints is chosen for the braid and the center conductor for maximum service life and optimum electrical stability. Unless the test system or component needs to consider intermodulation, the connector must generally use high quality stainless steel instead of copper for long life. The use of steel connectors increases the number of insertions and removals, reducing the penetration of metal particles into the connector and causing changes in connector impedance. If possible, the SMA Series connectors should have a hard, thick outer conductor design to reduce the amount of squeezing that can occur without the use of a suitable wrench. Installing the sheath for the cable helps to avoid damage from squeezing, transitional bending or twisting, but in general the flexible sheath does not avoid the damage caused by twisting... this is also a failure of the connector/cable assembly. Common causes. Finally, the only effective way is to train how to use and maintain it properly for efficient and long life. It is not uncommon for customers to constantly change their specifications and performance requirements. It is normal to expect the best requirements in all aspects. Therefore, pre-customized strategies can help us filter faster. We will classify some of the more commonly used parameters in Table 1. This list is not completely covered, not every parameter is designed for test cables. For example, power processing decreases as altitude increases. If power is the preferred consideration and the maximum power of the selected cable is close to the minimum demand, we may need to consider whether the product is used for high altitude. A cable for outdoor use needs to be considered for the possibility of moisture and also needs to be resistant to UV rays. Moisture resistance affects connector structure selection (closed air cushions are recommended for both internal and external) and cable selection (TImes LMR-db waterproof braided structure is recommended). UV resistance requires special chemicals in the jacket material. The final application will decide which material to use. First, from the list of parameters, select those that must be met. Second, set the minimum or maximum specification limits, but don't overdo it. Otherwise it will waste costs or miss some options that may be perfectly suitable. Once the parameters are ranked in order of priority from the most important to the least important, those less important will be ignored. First, we need to choose the most suitable cable structure or technology to narrow the scope of supplier search. This structure or technology needs to meet the necessary parameters and indicators as much as possible. For example, if 250,000 bending life is the highest priority, semi-rigid coaxial cable is not a suitable choice and the relevant technology or supplier can be ignored. However, large companies such as the Age Microwave System, which can manufacture cables that use more than one technology or material, such as solid foamed polyethylene, wrapped polytetrafluoroethylene, and existing silica, offer us more options. In summary, we should remember that the more parameters that need to be considered, the higher the requirements for this parameter, the more detailed the study and the higher cost/longer cycle. Customers will insist that the product achieve the best loss, bending radius and bending life, which can only be achieved by modern technology. While these are important factors, a study of the need for key indicators has shown that for a one-foot cable, the loss of a solid polytetrafluoroethylene dielectric cable at 1 GHz is not bad, and the bending life does not need to be very high. The length or bending radius does not need to be small. Electrical stability during bending is actually very important, but it is often overlooked. A typical cable failure mode is that the connector breaks before the cable is damaged due to continuous bending. The SilverLineTM test cable meets the real needs of the customer. For typical failure modes, the cost is within your control budget and the stock is ready for shipment. SilverLineTM test cables of different sizes and lengths are currently used in customer testing and repair equipment. 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