About LMR Coaxial Cables

A little over 60 years ago, a company called Times Microwave Systems (TMS) was born in Wallingford Connecticut.  They made all kinds of wires and coaxial cables for many communications companies and the military.

First I want to make it clear that I do not work for or get paid by TMS for this article or any endorsement. I believe this coax to be the best for the money. I will never again use any other type of coax except TMS LMR type coax.  I use LMR-400 for all of my antennas, and LMR-240 for short inside jumpers between devices.  In the past I have used RG-8, RG-8X, Beldon 9913, and RG-214 coax throughout my 45 years in radio. I have seen how long different coax types last, and the kinds of losses they have. I have noticed how even the better Belden cables can leak and cause TVI and get into stereos, phones, clock radios, the bathroom pipes….etc. I have seen how they handle broadband antennas with regards to SWR.

Then I switched to LMR type coax lines. And all of those problems went away. I use frequencies from 160 meters through the 440 band with 3 different antennas. I am in a 4 unit apartment building in a residential area. My neighbors homes are less than 70 feet away. No matter what frequency I use, no matter what antenna I use, no matter what power or mode I use, none of my neighbors every hear the slightest peep from my radio station. I don’t even bother anything in my own apartment. This has not been the case for 45 years until I used nothing but LMR type coax cables.  I am not saying this will cure any problems you may have. As they say, your mileage may vary.  But it solved all of my RF troubles. My SWR on every antenna came down to damn near flat.

LMR Type Coaxial Cables

So I figured that any coax that can perform this well, deserved to get a mention in an article. So here we go. Take from it what you will.  But in my radio world, there is no other coax on earth except LMR from Times Microwave Systems.

TMS makes the highest quality coaxial cable for communications services including Amateur Radio.  The LMR series is a 50 ohm coax designed to replace lower quality coax cables. There are rumors of what LMR stands for. One site says it is from the old days at TMS when they contracted to Lockheed Martin to make coax for military radar and radio equipment, LMR meaning Lockheed Martin Radar coax.  Another site says is just means Land and Mobile Radio coax. But for all we know, it could be the initials of the first guy in the warehouse to keep inventory of the stuff.  Or it may mean absolutely nothing.

Never the less, LMR is quality above and beyond other coax cable manufacturers in it’s class.  Most coax cables use a soft PVC type of jacket. LMR uses Polyethylene jackets for better UV and weather protection guaranteed up to 20 years in the harshest weather elements. Most coax cables use bare copper, or tin or aluminum wire for their shield wire. LMR uses tinned oxygen free copper for a better conductor and long extended life.  Most coax cables use several strands of copper wires twisted together for their center conductor.  LMR uses a single oxygen free copper plated aluminum alloy for flexibility, high conductivity, and extended life.

Here is where LMR shines over the other guys. The insulator between the center conductor and the shielding wire determines the isolation and loss per foot between them. Most coax cables use a poly-foam with air pockets to isolate the two conductors. Poly-foam with air is a good insulator, but it can break down in extreme weather, and allow moisture to get between the two conductors. This begins the oxidizing break down of the copper in both conductors. Some of the LMR copycats like Commscope uses the same lower grade copper. And they use a foil wrapping around the insulator for extra shielding. The problem with Commscope and other copycats is they just wrap the foil around the insulator. The foil is loose and can be stretched, and ripped during rolling up and unrolling of the coax, or especially when making bends to go around corners. This separates the foil from the insulator and reduces the shielding effect. The coax can now leak RF.

LMR uses a closed cell foam poly dielectric as the insulator to prevent breakdown with extreme weather and age. This insulator also has a foil conductor tape that is bonded directly to the insulator that becomes a virtual 100% shield conductor at all times.  The bonded foil also acts as a weather and moisture shield. No other coax manufacturer makes coax like this. Not even Commscope or the other copycats. So when someone tells you that their Commscope cable is the same as TMS LMR, they just do not know the facts.

Now that you know how LMR is made and why it is worth the few extra pennies per foot, let’s talk about the different grades of LMR, and how they compare directly to the regular RG type coax. We are going to start with LMR-400 as it is the most popular upgrade for RG-8 and Belden 9913. You may smile when you see how close the measurements are between LMR and 9913, but consider what each coax is constructed from like we just talked about. LMR will last much longer in extreme weather conditions, and retain it’s specifications for 20 years. LMR bends easier. LMR has a far better shielding foil molded to the insulator. LMR is far more water resistant. The solid center conductor ensures more RF at higher currents…. Commscope, 9913 and the other copycats can’t say any of that.

LMR-400

The number (400) represents the outside diameter measurement of the coax. Most coax cables in this class like RG-8 measures 0.400″. LMR-400 actually measures 0.405″  LMR-400 is designed as an upgrade from RG-8 type coaxes.

• Coax Type    Shielding      Loss in dB per 100 feet at…
•                                     30MHz     146MHz     446MHz     2.4GHz
• LMR-400       90 dB           0.7          1.5              2.7             6.6
• RG -8U         40 dB          1.2         2.8            5.1           13.7
• 9913 air        90 dB          0.8        1.5            2.8            7.5

LMR-100A

LMR-100A is designed as an upgrade for RG-174 coax

• Coax Type     Shielding     Loss in dB per 100 feet at…
•                                     30MHz     146MHz     446MHz
• LMR-100A     90 dB          3.9            8.8             15.6
• RG-174         40 dB         5.5          13.0          25.0

LMR-195 and LMR-200

LMR-195 and 200 are designed as an upgrade for typical RG-58 coax. All 3 are the same 0.195″ diameter. The center conductor is slightly larger in the LMR-200.

• Coax Type      Shielding    Loss in dB per 100 feet at…
•                                     30MHz     146MHz     446MHz
• LMR-195         90 dB         2.0           4.4             7.7
• LMR-200         90 dB         1.8           3.9             6.9
• RG-58            40 dB        2.5          6.1           10.4

 LMR-240

LMR-240 is designed as an upgrade for RG-8X (Mini)

• Coax Type       Shielding    Loss in dB per 100 feet at…
•                                      30MHz     146MHz     446MHz
• LMR-240          90 dB         1.3            3.0             5.2
• RG-8X (Mini)    40 dB        2.0           4.5           8.1

LMR-600 and LMR-900

LMR-600 and 900 are specialty low loss coax cables designed for extra long runs, and uses on the higher UHF bands and up into satellite frequencies. But they provide extremely low losses on HF and VHF bands over very long runs of 100 to 500 feet.  LMR-600 has a 0.590″ diameter, and LMR-900 has a diameter of 0.870″. They require special connectors. They will not accept a typical PL-259.

• Coax Type        Shielding      Loss in dB per 100 feet at…
•                                         30MHz     146MHz     446MHz     2.4GHz
• LMR-600            90 dB           0.42         0.95          1.7             4.3
• LMR-900            90 dB           0.29         0.65          1.2             2.9

So that’s it folks. If you want the most power to get to your antenna, a better SWR, less noise, and les RF getting into every cheap piece of electronics in the neighborhood,  Get some LMR coax. But don’t get taken by the copycats. They cost less for a very good reason. Because their quality is less. They do not use the same materials that TMS puts into LMR coax. It’s just not the same stuff. The real Times Microwave LMR coax may cost more, but it is worth every penny.

 

Article by K3DAV originally available at http://www.k3dav.com/lmrcoaxialcables.htm