#pa #u3s Extreme power curve across the bands. #u3s #pa

Nik
 

I've been using my U3S for the last month or so, with the bifilar inductor installed, and 1 to 3 BC170's.  The rf output curve appears to be very fierce.  I get max power at 7MHz, but at 14MHz it has sloped away to less than 20mW.  I've now installed the 5W PA module, and replaced the winding on the toroid with the 25 turn option.

With both the U3S and the PA zero biased, and the Shaping option set to 20 140 (using a 13.8V supply), power is around 6W on 7MHz but only 200mW on 14MHz.

Is this normal, and if so is there any mod I can perform to change the output curve to something a little more even?

All input appreciated!

Nik M1DOX

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