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Below is my homebrew qrp atu. Its based around the T network and should handle up to 10 watts. On testing this atu using a 142 foot closed loop antenna i found it found a match better and smoother than my MFJ948 in the shack. The inductance switch seems very responsive as does the capacitance controls making tuning a breeze as its very easy to hear the optimum settings on each control.Will work with coax fed systems as well as a balanced line via the internal 4.1 balun. I have fitted a bypass switch and also a banana socket for random wires.The BNC socket you can see is for attaching the telescopic whip to use similar to a miracle whip.
Below is a view of the inside of the atu.The inductor is two stacked ferrite rings.Im unsure of the mix.This is wound with 17 turns gauge wire with a tap at every turn for the first 8 turns.There is then two taps at two turns apart followed by two taps three turns apart.This inductor is soldered directly to a 1 pole 12 way rotary switch and secured to the top case. The capacitors are miniture tuning capacitors with a tuning range of around 3-146pf and a max working voltage of 100vdc. The tune/bypass switch is a DPDT type. The 4.1 balun is 14 bifilar turns on three stacked T68-2 toroids.
Below is the atu being used with the 817 to a 142 foot closed loop. Tuning by ear is really quick and simple as the controls are very responsive and its easy to hear the optimum settings.On tuning from 80m to 10m by ear only i found i was getting the vswr to within 1.5:1 everytime leaving only slight adjustment needed while in TX to get a reading of 1.1:1
Schematic to follow....
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