Understanding VSWR and Power Reflection in Amateur Radio Antenna Systems
By
pera
Hand-rolled, kettle-boiled, baked to perfection. Worth every minute at the bakery.
Summary
This article examines the common misconception in amateur radio about power loss due to high VSWR (Voltage Standing Wave Ratio) when feeding untuned antennas. It challenges the widespread belief that reflected power from antenna mismatches is simply lost as heat, explaining instead that most reflected power is re-reflected at the transmitter and doesn't actually represent wasted energy. The article provides technical explanations about how transmitters and transmission lines work, discusses the role of antenna tuners, and clarifies that the real concern should be about maximizing power transfer to the antenna rather than minimizing reflected power.
Key quotes
· 4 pulledThe power generated by the transmitter enters the coaxial cable and runs towards the antenna. When it reaches the load (the antenna) it encounter a mismatch; due to this mismatch, some power is transferred to the antenna, while the rest is reflected back and therefore lost.
A tuner can be added between the transceiver and the line, but it will just 'fool' the transceiver to believe it is seeing a matched load, while the mismatch and the reflected power are still there.
The truth is that the reflected power is not lost as heat in the cable, but is re-reflected at the transmitter and keeps bouncing back and forth until it is either radiated or dissipated as heat somewhere in the system.
The real issue is not the reflected power itself, but the fact that the transmitter may not be able to deliver its full power into a mismatched load, or that the transmission line may have excessive losses at high VSWR.
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