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If someone has a high SWR, obviously their signal will not make it out as far due to reflections. However, they will still be able to hear relatively well.

I have noticed for receive, a high SWR may cause the signal to fade a small amount, but nothing compared to transmit.

How does SWR fit into the law of reciprocity?

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  • $\begingroup$ Also note that the most usual reason that a transmitted signal is reduced by high SWR is not because of some kind of loss in the system (though that is indeed there) it is because modern solid-state transceivers will fold back the power to protect the PA transistors. Thus, if you TX 100 watts but measure only 30 watts out that is likely because the TX has been folded back for most of that 70 watt difference. $\endgroup$
    – K7PEH
    Nov 11, 2014 at 15:57

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High SWR on the transmitter means that less power gets radiated. Received SNR (signal to noise ratio) is degraded.

High SWR on the receiver side means that both signal + noise reaching the antenna are equally attenuated when reaching the receiver. As long as you are still above the receiver's sensitivity, the SNR is practically unaffected.

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Now if you think of a RF transistor that has 5 ohms of input impedance and the gain of the transistor is about 20dB over the specified band when the input is matched to 5 ohms. SWR, the measure of the reflected wave will be high because you are measuring it with a 50 ohms network analyzer but you will get the highest transmission(S21).

To be more precise if the device does not have active components(passive) ====> Bad SWR, Bad Transmission.

On the other hand if the device has active components you can't say anything by looking just at the SWR.

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  • $\begingroup$ It's entirely possible to have a passive system with an impedance of other than 50 ohms. Also, a 5 ohm receiver and a 5 ohm antenna is a 1:1 SWR. If your network analyzer tells you something different, it's either broken or you don't understand how to use it properly. $\endgroup$
    – Phil Frost - W8II
    Dec 1, 2014 at 19:32
  • $\begingroup$ Yes you can have it but if you read his question properly it says about an SWR measurement and all the datasheets give you a specification that they have measured under 50 ohm impedance otherwise you can't set the standarts. İf you have a source impedance that is complex conjugate to the load you will have 1:1 VSWR. I didn't say you can't have a passive system that is different from 50 ohms. Thats why we have something like SWR measurement. In passive systems like couplers or so you can get anything INSIDE the smith chart. Please read carefully before commenting. ;) $\endgroup$
    – mblackplum
    Dec 1, 2014 at 20:46
  • $\begingroup$ There are many ways to measure SWR, and not all of them involve measuring the impedance with a network analyzer then calculating what the SWR would be with a 50 ohm load. For example, one could scope the transmission line and measure the SWR graphically. One could also use a pair of directional wattmeters. There is no 50 ohm "standard SWR". If you are reading SWR from a device that assumes a 50 ohm system when this assumption is false, you are misusing your test equipment. $\endgroup$
    – Phil Frost - W8II
    Dec 1, 2014 at 20:53
  • $\begingroup$ Then you say you can connect a 1 ohm input impedance wattmeter to a lets say 30 oh input impedance device and say SWR xx:xx . Measuring SWR graphically is tha same too and the graphic is based on different frequencies i mean the x-axis is the frequency or you can look at it from a smith chart. When you buy an RF component and it says 1:2 VSWR which impedance is it based on? just a simple question . $\endgroup$
    – mblackplum
    Dec 1, 2014 at 21:04
  • $\begingroup$ I'm pretty sure any component that specifies "1:2 VSWR" was not specified by someone who really knows what VSWR is. $\endgroup$
    – Phil Frost - W8II
    Dec 1, 2014 at 21:29

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