I think you fellows are getting too serious is it time for this???
*** YT Video ***
LOL, that song and similar video was posted
many pages ago, you missed it.
I made progress on the software and have a somewhat operational core but I have more tweaks to do, and of course need to move to a bigger display. I added a button which triggers an ISR that sets the cal factor and coupling factor for the band you wish to use. I'm still futzing with the calibration as I will explain below. The screenshot shows its operation. Some of the info is for debugging and will not need to be shown on the final screen, such as PF (coupling factor of port) and CF (calibration factor for the band).
As shown it's measuring the transmitter of a Yaesu FTM-7250D on 2m band. The radio is on the high power setting. I previously measured this on my hp 437B as 44 W, the project meter reads 42.2 W. So that's an acceptable reading for now, but I have more tweaks to do.
The project should work up to 200W, and the signal the AD8307 sees is (input - 50 dB) port coupling.
200W is +53 dBm, port output would be +3 dBm
100W is +50 dBm, port output would be 0 dBm
50W is +47 dBm, port output would be -3 dBm
etc.
However, the response of the AD8307 isn't as linear as one would like in the area around and above 0 dBm as seen on the chart (circled in pink), mostly for the higher frequencies. Some of this is obvious from the chart but it's also present on a smaller scale that the chart doesn't reveal as readily.
So, after a lot of playing and measuring, I came up with a solution for this project. I added a small 10 dB SMA attenuator on the output of the FWD port so the port will be -60 dB now. This will shift all power readings down 10 dB (blue line on chart) and so move the high end of what I want to measure away from the troublesome area. This will not be a problem for the AD8307.
I need to measure from 1W (+30 dBm) to 200W (+53 dBm). The output from the port before this mod would be -20 to +3 dBm. After adding the 10 dB att., the output will be from -30 to -7 dBm, and should give me a much more linear response for the higher frequencies, eliminating any "gamesmanship" needed in the software to account for non-linear curves.
Now I will re-check all the cal factors for each band and see how it looks.