I wanted to check the actual power output on my old (serial #118) sBitx. I built a simple RF detector using a 1N4007 diode and a 10nF capacitor, with the rig running into a 50 ohm dummy load. I found a very helpful note from Hans Summer that described this measurement.
After all the caveats in his note, I decided my setup might "still be used nicely for ballpark and for relative measurements of RF power level." Making some meaurements and preliminary calculations, I decided to try to set "scale" values in hardware_settings.ini that gave me 5 watts out on every band, with the sBitx drive control set at 50. I used CW mode for my tests. 5 watts was an attractive taget because I can claim to be running QRP on all bands, and it might be a good level for driving a higher power amplifier.
I made a table to collect data, and started to experiment with scale values in hardware_settings.ini. I worked out several formulas to predict new values based on measurements, but they were not really helpful. It did lead me to collecting power measurement over a range of scale values though, and then I just eyeballed the data and got to the final numbers.
This table shows I can now set the drive to 50, and get just over 5 watts out on 80 through 10 meters.
(see drive_50.jpg)
With the same hardware_settings.ini scale values, I can turn the drive up to 90 and get the following power out.
(see drive_90.jpg)
With drive level = 90, power output is no longer flat across all bands. But I am satisfied that I am still under the rated power output for my sBitx on all bands.
This graph shows the scale value in hardware_settings.ini, and the power output at the two different drive levels across the bands.
(see sbitx power cal.jpg)
--
Mike KB2ML
