Terminating LMR-900

LMR-900 is a low loss 50 ohm coax that works great for many applications. At 30 MHz, the specifications state this cable is capable of 8.89 kW of average power and .3 dB loss per 100″ (.9 dB loss per 100 meters). Even though this cable is almost 1″ in diameter, it has an installation bend radius of 3″(76.2 mm) and a bend radius of 9″(228.6 mm), if the cable is repeatedly connected and disconnected to equipment.

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The inner conductor of the the LMR-900 is hollow. This helps reduce weight and increases flexibility. The outer braid has a waterproofing compound (also know as icky pick)that repels water if it penetrates the outer jacket.

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The connector used in this post is the Times Microwave Systems EZ-900-NMC-2-SP. This is a clamp style connector and does not require any soldering. It comes with 2 lock nuts; so, it will work with the LMR-900-DB and LMR-900-FR.

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The easiest way to prep the cable for this connector is with the ST-900C strip tool. It is easy to get the proper prep every time. If you do not have the strip tool, trim the jacket back .425″(10.8 mm). Be careful to not cut into the outer braid.

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Before inserting the cable in the lock nut make sure to lubricate the o-ring on the inside of the nut. Once lubricated push the cable in the nut until the end of the cable is flush with the edge of the lock nut.

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Flare the braid out to the tapered edges of the lock nut. If the inner conductor is deformed from cutting, now is a good time to fix it. Lubricate the o-ring on the outside of the lock nut.

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The bag that contains the lock nut will also have a center conductor pin. This needs to be installed in the front part of the connector.

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Push the center conductor pin into the center conductor. Thread the connector by hand at first then use a 1 1/4″ wrench and tighten to 180 in-lbs.

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The kit also includes a piece of heat shrink. Shrink it around the back part of the connector. This is a little extra protection for moisture. Even though this connector has o-rings and is supposed to be water tight, I like to wrap connections that are exposed to weather with a good rubberized tape. Finish it off with a good quality outdoor electrical tape on top.

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Links

https://www.timesmicrowave.com/DataSheets/CableProducts/LMR-900.pdf

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