This is my second own-built antenna tuner. The first one was the well known DF3OS QRP antenna tuner. In this case, I used the tune part from Hans and also the SWR meter from John(G0WQR). Therefore this is merged version of both.
I used the John’s SWR meter, becouse the results compared to the MFJ’s analog SWR meter were the best. In case of genuine SWR meter within the Hans’es project based on toroid inductor, I couldn’t reach acceptable measurements for some reason.
Please have a look at schema:
You’ll note two double-switches. The first one is for DIrect/Tune mode, the 2nd for SWR measure. This is becouse from time to time I need to use resonant antenna without any tune elements between the TRX and antenna itself. In such case taking two devices (tuner and SWR meter) isn’t comfortable. Here you are the two functionalities in one chassis. You can measure SWR with straight-forward connected antenna or turn the tuner on.
How to calibrate the SWR diode? This can be done with potentiometer used within project. The expected behaviour is that LED diode should’t bright at all with perfect SWR. I used the MFJ antenna tuner (MFJ941E) to compare the measurements. In my case the diode starts to shine when the SWR inreases to c.ab. 1.6:1 . Please try to use ultra-bright LED. It should improve the measurements.
Jakub/SP5TOF
