Thursday, June 23, 2016

From the man, Michael Pettersen, himself:

A common mistake in wireless microphone installation is the use of high-loss antenna cable, such as RG58, for long cable runs to remote antennas. The signal loss in an antenna cable run must be as low as possible, preferably 5 dB or less. At 500 MHz, a 100 foot run of RG58 has an unacceptable signal loss of about 11 dB.

For long antenna runs, RG8U cable or RG213U cable is recommended. For the installer, these cables have two primary drawbacks:
1) A cable diameter of ½ inch, i.e., it takes up a lot of room in conduit.
2) A large bend radius, i.e., it does not go around corners easily.

Times Microwave Systems, a company based in Connecticut, offers an attractive alternative to RG8U/RG213U. The cable model is LMR-240-LLPL; LLPL = Low Loss Plenum. This cable has a diameter of only ¼ inch, has a small bend radius, and is approved for installation in a plenum air space. LMR-240-LLPL for indoor use has an orange outer cable jacket. For outdoor use, the cable jacket is black.

For a 100 foot cable run, LMR-240-LLPL has a loss of 6.3 dB compared to 4.2 dB for RG8U/RG213U.

LMR-240-LLPL is expensive at $3.50 per foot. However, the LMR-240-LLPL small diameter and small bend radius will often reduce the cost/time of installation.

Signal Loss per 100 feet of cable at 500 MHz
LMR-240-LLPL: 6.3 dB for a 100 foot run
LMR-300 Series: 5.9 dB for a 100 foot run
Generic RG8U cable: 4.2 dB for a 100 foot run
Generic RG213U cable: 4.2 dB for a 100 foot run
LMR-400 Series: 3.8 dB for a 100 foot run
LMR-500 Series: 3.0 dB for a 100 foot run
LMR-600 Series: 2.4 dB for a 100 foot run
LMR-900 Series: 1.5 dB for a 100 foot run

Note that Times Microwave sells the appropriate BNC connectors and crimping tools for the entire LMR series of 50 ohm antenna cable.

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