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by disinfoniacs #69 & #1
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Impedance is an important concept in radio and electronics, as it is the resistance to alternating current in a circuit. When it comes to transmitting radio waves, you want to provide the path of least resistance through your feedline and antenna to ensure the maximum amount of energy is transferred from your transmitter to the antenna.
Ham radio operators use a metric called standing wave ratio, or SWR, to measure the degree of impedance matching between the antenna and the transmitter. SWR is expressed as a ratio, with a reading of 1:1 indicating a perfect match between the antenna and the feedline. A perfect match means that all of the energy from the transmitter is transferred to the antenna and none is reflected back.
It is important to strive for an SWR reading as close to 1:1 as possible because at 1:1, the transceiver delivers maximum power to the antenna, and this is the point of maximum efficiency. Higher SWR readings can cause energy to be reflected back to the transmitter, resulting in power loss and potentially damaging the transmitter.
SWR can be measured using an SWR meter that is placed in line with the antenna, or by using a directional wattmeter that can determine whether the feed line and antenna are properly matched. The SWR reading is expressed as a ratio of the maximum voltage to the minimum voltage on the transmission line, with a perfect match resulting in an SWR of 1:1.
When there is an impedance mismatch between the feed line and antenna, the SWR reading will be higher than 1:1. For example, an SWR reading of 4:1 would indicate an impedance mismatch, which means more than 40 percent of the transmit power is being lost before it reaches the antenna. This power loss is converted into heat, which can damage the transmitter or other components in the system.
If you have a solid-state amateur radio transmitter, it is designed to reduce output power as SWR increases to protect the output amplifier transistors. This protection mechanism helps to prevent damage to the radio due to an impedance mismatch. As such, it is essential to monitor SWR levels regularly and strive for as close to a 1:1 match as possible to maximize the efficiency and effectiveness of your radio system.
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