Estimate Power Efficiency from only your SWR reading on your radio of the Transmission Coax System

Tools to use to estimate the power delivery of your coax system to you antenna using only the SWR reading from your radio. There are very good software and antenna analyzers that give you many parameter's to predict how much power is being reflected back and forth (SWR) and lost in the coax (dB) system. The antenna is tuned for one specific frequency, as long as your radio is on that exact frequency and your coax is in good shape you will have very high performance. Once you change frequencies, now you will start to see an mismatch between the radio and the antenna, this mismatch is normal in HAM, the artifact (change) that you see is the SWR reading will start to increase because now some of the power is not able to be radiated at the antenna.

If you are interested let me

This video shows some of the building blocks I’m learning (and I hope are correct) to allow me to know approximately how much power is making to the end of the coax. This video considers the coax loss and the impedance mismatch that results in a higher than 1.1 SWR.

When the antenna, coax and radio are all on a balanced feedline only the coax loss is considered, when the radio changes frequency, and the antenna does not this creates a situation where some nonproductive power occurs along the feedline resulting in a higher SWR, this higher SWR can be used to determine the Return Loss, and then Transmission Loss, from the (dB) Transmission Loss combined with the coax loss it maybe possible to derive a number of how much RF power is making it to you antenna.

The iGMini software works with the MFJ-225 Antenna Analyzer. This allows you to look at a wide spectrum of the frequency range and see the SWR and Return Loss. With the SWR and Return Loss combined with the coax loss you can predict about how much power is making to from your radio to your antenna.

With just the SWR reading on your radio you can determine the Return Loss, and from the Return Loss you can derive the Transmission Loss. With the Transmission Loss in dB, you can combine the Transmission Loss in (dB down from full power) + the (dB loss of the coax) by combining the Transmission Loss and Coax Loss into a (dB) value you can now approximate the amount of power reaching the antenna from the radio.

I hope all of this is somewhat correct. I’ve been studying very hard to understand this, let me know if I mis-stated something I will correct it ’73 from KI5JUF.