Each antenna has an impedance which is measured in Ohms which is typically something like 50 Ohms (Ω) or 75 ohms (Ω) for TV’s, This impedance must ‘match’ the ‘impedance’ of the radio, cable and antenna, when the radio, cable and antenna are the same the radio is said to be ‘matched ‘ If all the Parts are not matched properly the antenna system will not be efficient as a large percentage of the signal will be reflected back and forth along the cable. In this event it is also possible to damage the radio. To measure this we use a device called a VSWR or SWR meter. A VSWR meter works by comparing the max power and the power returning down the cable. It is said that A reeding of <1.5 is good you can get away with it being higher but the higher you go the less efficient and the more possible damage may happen to your radio.
To test your Radios VSWR follow the below steps
• 1 Adjust your radio to be close to the centre channel in the band you will be working in
• 2 set your radio to its lowest power
• 3 Lessen to make shore no one is using the channel
• 4 If the channel is clear press the Push to talk button (PTT)
• 5 Switch the VSWR meter to the set position – this is marked FWD, FORWARD or CAL
• 6 While pressing the PTT adjust the “Calibrate control’ so that the needle moves all the way across to the SET or CAL position. This should take just a few seconds
• 7 Switch the VSWR meter to the SWR position and read your antenna’s directly off the meter Scale
• 8 An VSWR of 1.5 or less is considered to be good