eli5:what is Vswr in Rf?
In: 3
Something to do with rf jumper connections. I’m not an rf engineer, but a tower technician. Dealing with this issue daily, basically replacing jumper clears that stuff.
Hopefully somebody can actually explain what this issue is
When you send RF through a transmission line (e.g. a coaxial antenna cable) you feed a waveform through the transmitter’s output connector into the cable. This wave then travels from the output connector through the cable to, let’s say, an antenna.
Now, at high frequencies (or better, at short wavelengths in relation to a circuit’s size) some effects and properties become non-negligible. One of the most impactful is the characteristic impedance. The transmitter output has one, the transmission line has one and the antenna has one.
If the values for all three components is a prefect match, all of the waveform generated by the transmitter goes into the transmission line, and all of the waveform reaching the far end of the transmission line goes into the antenna. All you have is one wave traveling from one end to the other of the line. Let’s say we just send a sine over the line. If you were to draw the waveform at every moment in a long enough time-frame along the line, you’d get a sine, then another one, and one after another you’d end up filling up a fat black line with sines. Along every point of that line, you’d measure the same maximum voltage, the peak voltage of the sine.
If there is an impedance mismatch, some of the waveform is reflected at the surface where the mismatch happens, let’s say at the antenna connector. The reflected portion of the waveform travels back. Now you have two waveforms traveling in opposite directions. If you add them to a resulting waveform, you get a standing wave pattern along the line. We no longer have a constant maximum voltage along the whole line, but different possible patterns depending on the reflection.
This gif could help visualizing this effect (red is the sum, haven’t seen it on the english version):
[https://de.wikipedia.org/wiki/Datei:Standing_wave_SWR_4_(forward,_reflected)_open.gif](https://de.wikipedia.org/wiki/Datei:Standing_wave_SWR_4_(forward,_reflected)_open.gif)
So, VSWR is a possible way of characterizing the impedance (mis-)match between RF components.
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