Low Loss (LMR)

Along with the many types of coax cables there are to pick from, there is also an assortment of different coax connectors. When selecting a connector, you need to make sure you select one rated for the cable you are assembling. The back end of the connector that attaches to the coax cable needs to be the right size for installation. If the connector is too small, it will not fit. If it is too big, the connector will not secure properly and can be pulled off or even just fall off.

The type of connector you need will be determined by the equipment used with the coax cable. A television coax connection, for example, uses an F-type connector as the industry standard. Not every connector can be used with every type of coax cable, but all types of coax cables do support multiple types of connectors.

Every connector comes in two versions, male and female. A male connector will have a pin in the center while a female connector has a hole. If you are using an RP (Reverse Polarity) connector, this is switched. Male RP will have the hole while female RP has the pin. The term “reverse polarity” refers to the fact that the hole and pin are switched. They do not change the polarity of the signal going through the cable.

RP connectors were originally implemented by the FCC to try to stop members of the public from using antennas and other equipment to boost their Wi-Fi signals, in violation of federal law. This worked for a few years but now RP connectors are just as available on the open market as their conventional counterparts.

Coax (coaxial) cable is one of the oldest types of cables, having been in use for over 100 years. Like ethernet, coax cables come in both solid and stranded versions, although they are usually solid. Only a few types of coax, namely RG58 and RG8, are available as stranded.

Most coax cables fall into one of two categories, RG (Radio Guide) and LMR. No one is 100% sure what LMR actually stands for. It could stand for a term, someone’s name, or just be random letters. There are many rumors and theories for what LMR may mean but nobody really knows for sure.

RG cables are labeled “RG#” with the number formerly standing for the diameter of the cable. For example, RG59 cable originally had a diameter of .059”. While these measurements have changed over the years, the names of the cables have stuck. There are many types of RG cables and this article will only review the most common variants. Typically, RG cables have a 50 or 75 ohm impedance. Some off-shoot cables have different impedance, but all the standard RG cables covered here will be one of those two.

LMR cable is owned by the company Times Microwave. While the cables and name LMR are their property, other companies will frequently make equivalent cable, such as ShowMeCables EMR cables. These cables are labeled “LMR-#”, with the number being a rough estimate of the cable thickness. For example, LMR-400 has a 0.405” OD (outer diameter). LMR, like RG, has a few main types that this article will cover but off-shoot versions are also available.