The easiest and most accurate method of measuring the resistance of a UHF antenna is to use a digital multimeter. Measuring the resistance gives you the level that the electrical current is being impeded or hindered as it travels down the cable or circuit. Knowing the resistance will help you determine if the antenna is functioning at its fullest capacity or of there is a problem with the cable or antenna.
Turn off and/or disconnect any power source from the antenna prior to testing.
Determine what the preferred resistance is referring to the manufacturer specifications of the owners manual for the antenna.
Turn on the digital multimeter. Set the multimeter selector dial to the Ohms readings and to the range which will include the desired resistance obtained from step one. The Ohms setting will look like a horseshoe or the Greek symbol for Omega.
Example: If the desired resistance for the antenna is 450 Ohms, then set the selector dial to read a range that includes 450 Ohms.
Touch one test probe to the center conductor on the coaxial cable to the antenna and simultaneously touch the second test probe to the outer conductor on the same coaxial cable. Read the display while holding the test probes in place to get the resistance reading.
For example, if the desired resistance is 450 Ohms, but the reading on the display is zero or less than 450 Ohms, the antenna will not function at its peak performance and maintenance or repair is needed.
Turn off the multimeter to preserve the batteries.
Make sure that there is never any electrical power running to the device you are measuring as this could damage the device, multimeter or cause personal injury if the current is high enough.