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Old topic, but I need the guidance. I'd like to see the algorithm or the spreadsheet. 40w is just a littlte too low for me I'd like to mod the ATU-100 for 50w. If I change to 7 turns on the tandem coils and set the max power to 50w, do I also tell the MCU that I have 7 turns via setting Cell 31 to "07"? Thanks, if anyone is still following this old thread.

Stuart, you can use 100W tuner with 50W power with no any changes.

But if you want to set a tandem ratio to 7 you must change also appropriate cells also because it is the base of correct power calculation.

HI, thanks for the reply. I understand the power less than 100w. I'm going to run this with my (tr)uSDX and my Chinese USDX/USDR, and my Xiegu G90. I was really just asking for the basis of the turns ratio, min / max power settings, and how the math works. I have to do the mod, since my USDX radios can't initiate the Tune with only 1 to 4 watts. Actually, I did just set the FW without going to 7 turns on the xformer and tested it. It worked pretty well, getting me to <1:1.7 in all the bands use. I was told to do the turns change to match the tuner's? design.?

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I've read all the data I can find:?

Stock

Max Power: set to 00 (disabled)

Min Power: set to 5 watts

Transformer turns to establish the max voltage to the MCU: 10 turns. (actual turns and what is set in the FW cell).

Without any discussion, the original design paper says "10 turns on the transformer, 10 turns set into the turns Cell, Min power 5 watts). Good for a max power of 150 watts". Stock, the MAX power cell is set to 00, which disables any check for max power.?

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Most of the write-ups are 40 watts max, 5 turns (actual), change FW turns from 10 to 5), establish 40 watts max in the FW cell, change MIN cell to 1 (so QRP can initiate the tune) and don't exceed 40 watts (now the ATU checks for power>40 and won't tune if above).

I read that if I want 50w, I should remove 3 turns to have 7 turns on the transformer, set the power MAX to 50, and MIN power to 1 like above.?

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I like to understand what I'm doing usually by looking at any calculations or empirical tests done. I read about an excell spreadsheet discussion about the actual power / turns relationships, but couldn't find it. But, I want to get this done. So;, I've already gone down to 7 turns on the xformer, set the cells to 1w MIN, 50w MAX, and 7 turns.?

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I'm adding the BYPASS and AUTO buttons. My stash of old bypass capacitors are huge for 100nF (0.1uF). My caps are bigger than my micro momentary pushbuttons. So, I ordered a new kit of modern, smaller caps. I'm not going to try and put the SMD caps near the B1 and B2 ports. I'm going to put the bounce caps at my two switches. Should be good enough. Waiting on those to come tomorrow before finishing this.?

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Thanks again, Stu, KD5HVO

Stuart, if you wanna use 5 Watts or less for tune you have to make some changes, known as QRP mode. In any other cases use stock values . Will work fine for 20-40-50 Watts.

Well, I just put blinders on and followed what everyone else said to do for the QRP mods. I wanted 50 instead of 40 watts. So, I pulled 3 wraps off the transformer (for 7). I programmed the firmware for 50 watts max, transformer ratio to 7, power Min to 1.?

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I added micro buttons to my ATU-100 faceplate. I added the 100nF caps to each push button. I ran the switch wires to B1 and B2. I grounded the switches to the same ground post as the TUNE button.?

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It works! I have a ATU-50 now. I tuned my Xiegu G90 to my G5RV on 80, 40, 20, and 15 Meters using 2 watts. I'll do the others later. Tuned down to the around 1:1.5 SWR or less. I just wanted to check the range of tuning. Next will be my (tr)uSDX, and then my USDX/USDR (when I finish repairing it).?

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I tried the BYPASS and AUTO buttons. They work fine, with the correct DOT and UNDERSCORE visuals on my OLED display. This is a 2? years old Chinese built ATU.

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On to the next project. Thanks for the help and answering my questions.?

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Stu

KD5HVO

Los Alamos, NM

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