Times Microwave recently celebrated the 30 year anniversary of its LMR Cable Series. This disruptive cable set the benchmark for RF coaxial interconnect solutions in the 90's. everything RF recently interviewed Tony Fedor and Kevin Moyher who are Product Managers at Times Microwave Systems to learn about the evolution of this cable.
Q. Congratulation on the 30th anniversary of your LMR coaxial cable! Can you tell us more about this cable, its specifications, and its features?
LMR® is a very low loss, flexible cable. The nitrogen gas injected foam core ensures stability of the dielectric over the long term. It also has excellent mechanical and physical performance and offers much better electrical performance than what’s available with traditional RG cables because of the high-quality materials used in manufacturing.
Q. What made Times Decide to develop the LMR Series of Cables?
We developed LMR cables as an alternative to some other traditional RG cables and stiffer corrugated copper cables on the market. In addition, many people were using a cable with an airspace dielectric, which was not a good overall cable for outdoor use thanks to moisture ingress. So, we introduced LMR 400 as our entry point to address these issues, and as different application requirements came up, the family of products expanded.
Q. How does this cable compare to other similar cables in the market, and what do you think sets it apart?
Other cables on the market tend to be RG cables, which have higher loss and are poorly shielded with PVC jackets, so they’re not meant to be outdoors. They’re not outdoor weather cables. In terms of the corrugated cables of similar size, they’re either very stiff or very fragile and susceptible to kinking. With LMR cables, we wanted to address the weaknesses of what was out there for similar size cables. We made LMR cables easy to terminate and highly shielded, so it checks all the boxes of what customers would need for a rugged, wide frequency general purpose indoor or outdoor cable.
One of the strengths of the LMR product line is it offers a complete package, from the cable to the connectors to the tools for termination and installation. An RF interconnect is only as good as it’s weakest point, so the tools for creating that cable-connector transition are crucial. Since many cables have to be terminated in the field, whether they’re run through a bulkhead or need to be custom lengths, we put ourselves in the shoes of the end customer and gave them all the tools they need to make the best possible RF interconnect.
Over the years, we’ve seen a lot of clones and copies of LMR cables. As LMR cables became more popular, everyone wanted to copy it. These copies are perfectly fine as long as it’s not a mission-critical application, or if you don’t need a system to last a long time outside. Since those plastics and dielectrics don’t have the UV resistance they need, they’re going to break down. They might test fairly similar up front but won’t last because they’re not made of the same quality materials.
Q. Are there specific markets for which this cable was developed? Where is it used now? Which segment is the largest?
The original market LMR cable was developed for was two-way radio public safety, and it’s now branched out into so many different environments with higher and higher frequencies. Radar systems and vehicle communication and public safety are some of our biggest markets, but LMR cables are used in so many types of applications nowadays. It’s for anything in the wireless world where you’re hooking up an antenna.
Q. Can you tell us about the manufacturing process of the LMR series cables? What materials are used to make this cable, and how have these materials changed over the past 30 years?
The materials for LMR have changed, and they haven’t at the same time. Any of the changes have come from advancements in the materials we use. When the product line was first released, we used polyethylene jackets to make it ideal for outdoor applications. It’s a well-known UV stable material, and ideal for broad temperature ranges outside. Polyethylene has remained pretty consistent over many decades, even though there have been some modifications and cleaner versions, it is overall the same product.
Same with the materials for our foam core. From that perspective, the materials haven’t changed all that much. The biggest changes have been with our flame-retardant cables. Over the years, there’s been a drive towards non halogen, low smoke flame retardant materials.
Q. How do you ensure the quality and consistency of the LMR coaxial cable, and what measures do you take to ensure that it meets industry standards?
We understand what matters to customers, and it’s important to us to create consistently good product. We used to be almost all military cables, and we brought that knowledge and expertise over to the commercial side for LMR cables. While other companies focus on how cheap they can make coax cable, we have the perspective of really understanding RF and focusing strictly on coax, including the connectors and tools. We take ownership for the connection between the antenna and the equipment.
When manufacturing, there are a lot of process steps we take that others don’t, a lot of little details we’ve paid close attention to that many others ignore. For example, even though we buy our conductor at an exact size, we still redraw it through a draw die to ensure it’s the perfect diameter. We pressure the jacket into the braid to force all the air out so there’s no path for moisture to move through, and that helps create mechanical stability when the cable is flexed. It’s the 30-year anniversary, and we have cable out in the field that’s been there those 30 years that still looks as good as it did when it was installed.
Q. How has the technology used to manufacture LMR series cables evolved over the past 30 years, and what changes have you made to your manufacturing process to stay up-to-date with these advancements?
Over the years we’ve made a lot of improvements from the original core manufacturing technology. When we first started making LMR, we used nitrogen tanks for the nitrogen gas injected foam core, and when a tank rank out, we had to shut down the whole line to change it out. You can imagine the high levels of scrap that generated and how that had an impact on consistency and cable run lengths. Now we have a nitrogen extraction system, so we can extract nitrogen out of the air and run a continuous process.
Braider technology has been the same for a hundred years; the changes we made were making them all individual instead of on one main drive. If there’s a braid spike, now we can track exactly where it occurred and fix the problem. We’ve also added sensors to indicate when a bobbin runs out and shut down the machine instead of having operators manually checking each braider.
Those are only two examples of the changes we’ve made over the years, but there have been countless more. Our manufacturing process has seen a big improvement from when we first started thanks to these process controls to help us ensure consistency. Continuous inline analysis that we didn’t have when we first introduced this product enables us to look for every tool to improve the overall process.
Q. Can you tell us about some of the most interesting projects in which this cable has been used?
LMR cables have been used in so many interesting applications over the years that it’s hard to narrow it down to a few. From mining equipment communications to Wi-Fi on commercial airplanes, LMR has been used pretty much everywhere. Surveying, for example, used to be done manually, but now it’s run by GPS to layout roads or construction, and LMR cables run to those GPS antennas. One of the more unique applications has been for agriculture. An agricultural company embedded antennas in their fields and used LMR to transmit the data, and those antennas report on the moisture content in the ground so they know where to irrigate their crops. And more recently, as more and more satellites are launched, we’ve seen a growth in radar stations to monitor space junk and notify companies if their satellites will collide with said junk.
Q. How has this coaxial cable series evolved over the 30 years? What plans for the future? Will there be more products launched within this series?
After the introduction of LMR 400, the cable series grew to include about a dozen different cable sizes. All the growth in the product line has stemmed from two factors: a need from customers, and advancements in materials. We added both smaller and larger cable sizes to address frequent issues with other cables on the market, all the while optimizing our own cables with lighter weight, tougher, and more flexible materials.
RF is RF. It might behave differently at different frequencies and become more demanding, but in the end it’s still the same base concept. With the constant drive higher in frequencies and performance, the future we’re seeing is meeting the demands for latency and quickly processing information. Some things we’ve already diving into like bundled cables and multiport connectors for high-density applications. Down the line, we’re looking at potentially optimizing some jacket materials to make the product tolerate higher temperatures with better performance.
We don’t want to stand still and as technology evolves, we want to evolve with it.
About the Authors
Kevin Moyher is a Product Manager for Commercial Products with Times Microwave Systems. He has more than twenty years of experience developing RF interconnect products.
Tony Fedor is Product Manager for LMR and Specialty Cable at Times Microwave Systems. He has extensive experience working with high-performance coaxial cable interconnects and related technologies.
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