Circular SWR ruler

The SWR ruler I made.

I'm not the first one writing about this ruler. IW0FFK mentioned it on his webpage/blog before. However I did not read that before and it was PA3GTM Hans that gave us the DIY "kit" on our radioclub evening. At first I was staring at it and although Hans made a working ruler I was not shure what to do with it or how to use it. After a good day of working the mind is not that sharp anymore I think. At home I was able to do a research and have a quiet look at it the next day. I assembled the ruler "kit" and played with it when transmitting myself and comparing to see what use it would have. And indeed it is a handy gadget every HAMradio operator should have in the shack.

Curious? Check out the website from TK5EP.

Well, what to do with it? I always like to know how much power is lost at a certain SWR. And that is not that much, the ruler shows you. Set the window for SWR 1,6 at the arrow. The blue outer disk gives input power and the black inside disc shows what power you lost with this SWR. In my example case 25W (PSK31) in then 1,4W is lost. You can also view the gain/attenuation in dB. For example the max. output from my Icom is 100W (blue numbers on outer disc.), my Yaesu 817 gives max. 5W (black numbers inner disc.) the gain difference is more then 13dB. If you count 6dB per S-unit it is only a difference of approx. 2 S-units. Ever wonder how much difference there is between 100W and 1KW? Well, according this handy ruler it is only 10dB. That is less than 2 S-units.

Good luck assembling the "kit"