Re: Question About The 4 States Antenna Tuner

Jim, N5IB

Hi Dave,

First thing to do is determine if the problem is with the SWR bridge part or the tuner part. Unfortunately with this circuit you can' t test the just the bridge into a dummy load without having the tuner in-line.

Do you have an antenna analyzer or a separate SWR meter that will work at QRP power levels? If so, connect a dummy load to the ANT jack and switch the bridge OUT. Excite the tuner with your analyzer or with a QRP transmitter through your other SWR meter and see if you can tune for a match. If so, the Ls and Cs of the tuner part are OK and the problem is almost certainly with the bridge part. You could even do this with the antenna connected if you don't have a suitable dummy load.

NM0S used some cleverness in devising the bridge indicator, and I don't profess to understand it fully :^)) but that's not a new thing. It almost seems like yours is working "backwards" with the red LED showing forward power.

As someone else commented, if the LEDs light at all it's pretty sure they are installed correctly. But check that the other diodes (D1 and D2 in particular) are oriented correctly. And also double check that Q1 and Q2 didn't get swapped. Q1 should be a 2N3904 (NPN), while Q2 is a 2N3906 (PNP).

Also double check R5 and R6 ... easy to miss the color codes if the light is poor... R5 is 150 K (brown-green-yellow) while R6 is 1.5 Meg (brown-green-green) .

Keep us posted what you discover.

Jim, N5IB

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