Should You Worry So Much About SWR?

Should You Worry So Much About SWR?

I was never worried about SWR or Standing Wave Ratio during my first stint in Amateur Radio in late 1980s. That was due to three reasons: 1. I did not know much about SWR. 2. I did not have an SWR meter, though I did homebrew an SWR bridge later on and tested SWR using an analog multimeter. 3. Most of my Ham Radio operations were with a homebrew vacuum tube radio and vacuum tube radios are known to tolerate higher SWR than solid state radios. As a disclaimer, I did lose quite a few BD 139 final transistors of my VU2VWN QRP radio which was my first ever Ham Radio. Retrospectively, it could have been due to elevated SWR.

Moreover, I was using 75 Ohms television cable as feeder as that was the only one available locally and I did not even know that there is 50 Ohms cable for Ham Radio! I had never tuned my inverted V dipole antenna or horizonal dipole, most often in ‘V’ configuration due to the weight of the unsupported feedline! Still I had reasonable success with local contacts on QRP on CW/AM, while some of my friends could work plenty of DX with it. I could work a lot of DX, including the most difficult W land in those days, on CW with my 3 x 807 vacuum tube QRO running about 120 Watts, and dipole antenna.

In late 1990s when I purchased a commercial TM 261 VHF base station and a handy, I became more concerned about feedline, though still lacking an SWR meter for VHF. I moved on to RG 213 cable and ground plane antenna tuned and given by my local Ham friend. Still later I had used a 7 element Yagi with Gamma match, again, tuned and provided by another local ham friend. Then came a period of inactivity, to return back to Ham Radio in March 2023, with a renewed license and a lot of interest and some more free time. Moreover, I had become familiar with how to get information from Google, Twitter and WhatsApp, with plenty of inputs from the Ham Radio fraternity worldwide!

Though the old TM 261 is still working on low power, I have acquired a new IC 2730 dual bander radio. Now I have become really concerned about SWR as I do not want my new radio to pack off due to high SWR! I had also purchased an SWR meter which could measure SWR from HF right up to 525 MHz. So I started measuring SWR for each and every configuration. My CP22E commercial VHF antenna had a low SWR of about 1.1:1 on VHF. Then some of my friends told me that it will also work on UHF as third harmonic, just as the 7 MHz dipole also works on 21 MHz. My CP22E has an SWR of nearly 1.8:1 on UHF on sunny days. SWR on both VHF and UHF rises when it is raining heavily, making me more concerned. Still I do use it mostly for VHF transmission and UHF reception for V/U FM satellite operations, with fair results. UHF transmission for U/V satellites has been successful only on very few occasions, as expected.

It was with this background information, that I read with great interest, an article by KN0JI, titled “An excessively low SWR can kill you“! He has mentioned that our undue concern for SWR could lead us to repeated climbing on rooftops which could be really dangerous, especially in adverse weather conditions. In fact, in my second stint in Ham Radio I have stopped climbing on the ledge at first floor roof level where I used to place my VHF beam in early 2000, thinking of this aspect. I have opted for safety over performance and hosted all my antenna experiments on first floor terrace. The important part of KN0JI’s article is his news flash: ‘Your antenna system does not need to have a 1.0:1 SWR to function well!‘

He goes on to mention our two important concerns in case of SWR: 1. We do not want to burn out the final power transistor of our radio because of high SWR. In fact I have lost quite a few of them for my old homebrew QRP! 2. We want all the power from our radio to go out of the antenna and not get reflected back due to high SWR. He mentions that the first point is not much valid for a 21st century commercial radio which has a feedback mechanism to reduce power output or shut off the radio in case of high SWR. I think I have experienced this a few times in my IC 2730. Sometimes ‘UNLOCK’ appears on the screen and there is no power output when the SWR is elevated. This does not appear when I try again on low power with the same antenna. Many modern HF radios have internal automatic antenna tuners which can take care of SWR up to 3:1.

Regarding the second point of the power reflected back the antenna because of mis-matched impedance, KN0JI informs us that this power is not really lost. It will get re-reflected back to the antenna when it reaches the radio. The process is repeated until the power is either transmitted or consumed by the coax. He mentions this as a valid reason to use low loss coax to reduce power loss in the cable. That part can be easily accepted as that will also improve the reception of weak signals as in case of amateur radio satellite operations.

But I am not sure whether multiple reflections across the coax will impair the quality of the signal as I would expect mixing up of reflected signal and the new signal coming from the radio, just as if you are listening to music in a room with too much of echo. Anyway it is comforting to note that protective mechanisms built into modern radios would prevent damage at SWR up to 2:1 without any significant cut down of power. Even higher SWR may be tolerated in HF radios with an internal antenna tuner. I have seen a video online in which it was shown that the initial higher SWR drops quickly when the internal antenna tuner functions in commercial radio with automatic antenna tuner. So may be we can save ourself from multiple climbs to the rooftop. After all, you are more important than the radio! Link to KN0JI’s article is availble in the description box of the video.