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Frequently Asked Questions
FEMALE CONNECTORS, BULKHEAD CONNECTORS FLEXIBLE CABLES, CABLES <18 GHz INTERMATEABILITY of SMA, 3.5mm and 2.92mm Connectors What is the maximum size bend radius allowed? Specify a maximum of 0.500-inch "CLR" (centerline radius) or corresponding inside radius "IR". The IR is the CLR less 1/2 the cable diameter. Any cables previously designed with a CLR greater than 0.500" must be redesigned for a single size CLR not to exceed 0.500". IMPORTANT: Do not specify more than one size bend radius per cable. What is the minimum size bend radius allowed? Check and observe cable manufacturer's minimum bend radius. As a rule of thumb, 0.375" center line radius works well for both 0.086" and 0.141" diameter semi-rigid. Compact assemblies may require the minimum allowed bend radius.
What is the maximum degree of bend? The maximum degree-of-bend "DOB" is 180 degrees. What is the maximum number of bends? The maximum number of bends is 32 Are back-to-back bends allowed? Cables are formed by a "bend arm". The bend arm forms the cable around a circular mandrel much like you would bend a wire around a spool with your thumb. The bend arm is offset by few tenths of an inch to gain leverage on the cable, just as you might offset your thumb to bend wire around a spool. After each bend, the cable is progressively advanced and rotated as required to achieve up to 32 complex bends, in any of three dimensions. A short, straight section of coax must exist between each bend so that the bend arm can accurately place the correct degree of bend. If the previous bend has not advanced to clear the bend arm, then the bend arm will press on it and deform it at the next operation, this will also confound the current bend. It is for this reason that immediate back-to-back bends cannot be allowed. There must be about 0.2" of straight section between successive bends. In compact designs, using the minimum allowable CLR will usually allow some space in a cable design for the required short straight sections between bends. The automatic cable bender is designed to carry out bending operations within a tiny area, and tooling size is very small, even so, at least 0.200" of straight cable between bends is needed. Where absolutely necessary, back-to-back machine bends are possible with manual intervention, but at significantly higher cost. Can I specify any bend radius I want? Yes, provided you specify a center line radius (CLR) between .168" and 0.500" (or corresponding inside radius). Because of various request for odd size radii, and due to tooling wear, we machine our own bending mandrels for all of our automatic benders. Can cables be hand-bent to special forms? RF COAX INC. will only machine bend cables. RF COAX specializes in the efficient manufacture of high performance semi-rigid cable assemblies. All cables must follow the few design limitations outlined herein, so that our automated benders can be fully utilized. Is it possible to machine bend hand formable coax? No. Hand formable coax will not fully retain its machine-bent form. Only semi-rigid cable can be verifiably machine bent to exact dimensions. What cables are best suited for machine bending? All semi-rigid types are well suited for machine bending. Military applications most often specify a semi-rigid with a hardened copper jacket because it best holds its shape after bending. These are M17/133-00001 (0.086"), and M17/130-00001 (0.141"). On the other hand, a softer aluminum jacketed semi-rigid is sometimes preferred where the formed cable is intended to yield under stress, for example when fitted with tiny SSMP connectors. When not specified, our standard cable is an soft copper-jacketed cable, type M17/133-00007 (0.086"), or M17/130-00005 (0.141"). Why are female connectors more expensive than male connectors? Precision RF connectors designed for cable assemblies are generally male with some exceptions like SMP, and SSMP. Male connectors being more common are generally more available, and less expensive than female connectors. In addition to being less common, female connector can be more expensive to manufacture because of their more complex center conductor. The female center contact is usually intricately machined (turned, slotted chamfered) from expensive, hard Beryllium copper, not simply turned like a male pin. The female contact must additionally be heat treated in special fixtures to form and retain their inward spring grip. Why are female bulkhead connectors scarce or unavailable? Bulkhead female cable-end connectors are specified even less frequently than the plain female cable-end connector. 2.92mm, 2.4mm, and 1.85mm connectors already command high premiums in price, so a female bulkhead can be surprisingly expensive. As for availability, while found in the catalog of some connector manufacturers, they are often just "designs" and therefore not immediately available, and generally require large minimum orders of 250 units or more. RF Coax does stock some 2.4mm and 2.92mm bulkhead connectors. Are female panel adapters available. Yes. Female-female bulkhead panel adapters are readily available in 2.92mm, 2.4mm, and 1.85mm. The adapters are generally of the precision stainless steel type, have excellent VSWR, and when combined with an also readily available male-male cable, have for some time provided a practical solution to the bulkhead requirement. RF Coax does stock some 2.4mm and 2.92mm bulkhead adapters. Flexible Cables, and Cables < 18 GHz Why don't you offer Flexible cables, cables <18 GHz? We specialize in semi-rigid cables operating in the 18 to 65 GHz range. We also provide specialized services such as temperature cycling (preconditioning), phase matching (to very tight tolerances) and testing to 65 GHz. Our cables are manufactured by very highly skilled microelectronics assemblers with access to some very sophisticated expensive machinery, and electronic test equipment. Most assembly operations are completed under a microscope, and our standard offering connectors are mastered one-at-a-time, usually after several weeks or months of trials. Our emphasis is on performance and price, and on these fronts were are fiercely competitive. We simply could not serve our customers well to additionally compete in the area of more easily manufactured cables. What are the advantages of Low-Loss Cable? Low loss cable (expanded dielectric, AKA microporous dielectric) is considered more phase stable and is less lossy than standard solid dielectric cable. What are the disadvantages of Low-Loss Cable? Many. The spongy low-loss dielectric poses more problems than it solves. It does not support the center conductor well, especially around tight turns. At each bend, the inner conductor will pinch the soft dielectric, and draw closer to the outer conductor upsetting the cable impedance. Low-loss cable is poorly suited for use in compact formed assemblies. The dielectric will absorb fluxes, and alcohol during assembly, and during cleaning. It will absorb moisture if the assembly is left disconnected or is stored unconnected. Low-loss cable is less consistent in loss per foot than solid dielectric cable, and when improperly manufactured (more often than not) can be more lossy than standard dielectric cable. Because the spongy air filled dielectric is inherently less consistent than solid dielectric, phase matched cables vary more in length for the same delay per pair or set, sometimes and inch or more difference for a five foot pair having identical delay. Low-Loss cable is more expensive than standard cable, up to 3-times more expensive. The low loss dielectric upsets the impedance and so requires an offsetting larger cable center conductor, that in turn requires special (more expensive) connectors whose only excuse for commanding a higher price is a larger hole in the backside center pin. Alternatively low-loss cables can have a standard center conductor diameter, but an offsetting reduced inside diameter of the outer conductor making it much more difficult to bend. Low loss cables generally provide worse VSWR at the connector ends simply because cable end preparation without damaging the soft dielectric is difficult, and other aspects of termination are far less predictable. Low loss semi-rigid cable is a poor choice over standard semi-rigid except over runs of several feet AND where the approximate 10% less loss afforded by a properly manufactured LL cable is considered absolutely essential to the design. As for phase stability, that of standard dielectric copper semi-rigid is already very good. RF COAX stocks all types of LL semi-rigid, plated, unplated, modified inner conductor, modified outer conductor, but offers none unless it is specifically requested. Which of our products are RoHS compliant? Hand-Formable Cables: Generally any cable we sell that is described as "hand-formable" is manufactured to be RoHS compliant. Customers can expect to receive RoHS compliant product without specifically requesting it, and there is no added cost. Basically the traditional SN63 tin-lead solder is substituted out for high temperature lead-free solder alloy type 96.5Sn, 3Ag, 0.5Cu, or similar. While a higher soldering temperature is required, the heavily tin coated hand-formable type cables solder very quickly thus helping to keep heating time to a minimum. Performance and reliability that could be diminished by the effects of overheating are not compromised, nor is physical strength. In fact, the tensile and shear strength of the lead-free alloy is roughly identical to the tin-lead alloy it replaces. Which of our products are not RoHS compliant? Semi-rigid cables are not generally compliant, except by quotation on request. Tin-lead solder is standard on all of our semi-rigid cables. Not all connectors and cables traditionally assembled with tin-lead solder can also be manufactured with lead-free solder without compromise to either performance, reliability, or cost. Certain types of semi-rigid cable are very much affected by heat. Also, because the vast majority of our semi-rigid cables are used in critical applications such as military avionics, EW systems, radio telescopes, as well as laboratory, and other precision applications, we continue to use tin-lead solder unless we have quoted otherwise. The higher soldering temperature of lead-free solder requires careful selection of components, allowing for quotation on a case-by-case basis. Semi-rigid cables with 1.85mm or 2.4mm male connectors are just an example of configurations that we are happy to produce with no-lead solder on request, and at no extra charge or change in specification. How can I verify that no-lead solder was in fact used? Under magnification, no-lead solder that is properly applied appears less shiny, more grainy, and develops less of a concave fillet than does traditional tin-lead solder. Most inspectors have by now become familiar with the telltale appearance of a no-lead solder joint, and they know that regardless of this different appearance, the tensile and shear strength of the lead-free alloy is roughly identical to the tin-lead alloy it replaces. Will you build hand-formable cables with tin-lead solder on request? Of course. Generally all cables are built when ordered so we are more than happy to build to your exact requirements including solder substutition. Do you certify RoHS Compliance? Yes, a statement on our packing list serves to certify delivered products as RoHS compliant. Why don't you offer more items at you web store? The web store is intended to offer a sampling of some of our products, their typical performance specifications, and prices. All cables are actually built-to-order. This is because there are so many possible iterations of cable lengths, connectors, connector genders, phase matching requirements, temperature cycling requirements, and so on, that it is prohibitive to stock much of anything. The few cables that we show in our Web Store we must remain ready to make immediately, and ship within 2-3 days. It follows that we carry a huge inventory of connectors, and coax, plus we are prepared to build, test, and deliver surprisingly fast. The best way to get started with your particular need is to give us a call, send us a fax, or e-mail. For simpler requirements, we can firm up a requirement, and take an order right over the phone. You'll have your 18 to 65 GHz cables in a few days, machine formed if needed, and with test data. Wow! Why use the Web Store? The Web Store is a simple, convenient, and trusted way for the average person to order what are high performance commercial cables. Since processing orders can be expensive customers whom enter their own orders, of any of the basic cables offered online enjoy accelerated 10% and 20% discounts on just 5 and 10 units ordered, plus rapid 2-3 day fulfillment. Our intent is not to sell, sell, sell, but to offer some of the highest performance cables, at reasonable prices. Most often this means that you'll need to contact us with your requirements. In fact we make less than 5% of our sales online.
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