Optimizing power output

[DK2CW]

Hello,

I built the kit according to the schematics and also double-checked the windings on all toroids.
Then I measured power-output using a dummy load @ 12V. I measured with the on-board sensor and also checked the rectified voltage at the dummy load which confirmed that the truSDX measurements are correct. I noticed that on 20m, 40m and 60m I only got about 2,5 W. On 80m at 3,500 kHz I got 5 W and on 30m I got about 4 W.

I removed one turn on each toroid for 20m
and removed two turns on the first toroid for each 40m and 60m.

This increased the power on all bands to about 4-5 W.

Next I tried a few antennas. On dipoles the power was a little lower then on the dummy load, which can be expected I guess.
On a coil-loaded vertical the power varied. Sometimes it got lower and sometimes higher, up to 7,5 W depending on the bands. I guess in that case the on-board measurement does not provide exact values because of mantle waves.

However I have a few questions:

1.) Is this the expected behavior that the toroids need to be optimized for power?
2.) Are there any downsides like overloading the PA?
3.) Does this decrease the efficiency?
4.) Is it better to remove windings on the first or second toroid?
5.) Based on the low-pass the characteristic the power gets lower to the upper end of the bands. I have 5 W on 3,500 kHz and 3 W on 3,800 kHz. Is it okay to optimze the power on the upper end of each band?
6.) Can the power really get higher on some antennas like coil-loaded verticals or is it really a measurement error?

Thanks in advance for your help. And I really love the kit. So far it works really well!

[DL2MAN]

Hello DK2CW,

Ad 1) Yes, it is to be expected. Personal winding style and Core Tolerances make it neccessary to tweak for maximum performance.
Ad 2) A certain load creates a certain output power. If you stay below 5W@12V / 6W@13,8V you should be safe. However: Especially the LPF roll of and second harminic notch should be verified by something like NanoVNA. You can´t really measure the resonant frequency of the series LC (because it is around 10 Ohms, and NanoVNA is a 50 Ohm System), but the Insertion Loss at second harmonic can be judged.
Ad 3) Sometimes yes, sometimes no. Depending how your Filter Network is set up. Just activate in SWR Menu PWR Eff, then you´ll see efficiency immediately on your display....
Ad 4) For more output power, lower inductance of serial resonance coil, for bad harmonic suppression play with LPF Coil, but use NanoVNA to see what´s going on. see ad 2)
Ad 5) Yes, my Filters were optimized around CW portion of each band. It is totally OK, to optimize them for upper portion of the band, however: Be careful in the CW section then, because if you end up with 7W@12W in CW portion, you lose a lot of safety margin for bad SWR....
Ad 6) This is a measurement error

73 Manuel; DL2MAN

[W6LKB]

My unit is working and I've made both CW and FT8 contacts. But my power output is about 1.2W on 20M with 30% efficiency. On the other bands I'm getting:
30m 2.3w 58% eff.
40m 3.6w 68%
60m 0.6w 7%
80m 3.4w 50%

This is with 13.8v in the lower portions of the bands.

I tried taking 1 turn off L11 but it didn't improve my output on 20, it actually decreased it slightly.

I rechecked my soldering. I don't really care about 60m but would like 20m to get improved.

Any suggestions?

[DL2MAN]

I suggest reading this:
viewtopic.php?p=1686#p1686

73 Manuel; DL2MAN

[W6LKB]

I fixed 60 by putting the correct cap in C46.

[W6LKB]

I will go through the fine tuning process soon. But I can't get my 20m output increased beyond about 1.2 watts with 13.8v DC. I've taken a turn off L11 twice and adjusted capacitance at C10/C11 but neither is affecting my output and my efficiency is low 20's percent. The other bands seem acceptable. Would love some suggestions. Thank you.

[DL2MAN]

I will go through the fine tuning process soon.

This is where you´re misleaded: My suggestion is not a "fine tuning" process.
It´s the tuning process, following logic.
What you´re doing by randomly taking windings off, is just guesswork. How should anyone on the other side of the world give you a hint if you don´t check the filter curves ?
Also: If you "adjust" capacitance, you´re acting outside of schematic. Why would you do that ?

73 Manuel; DL2MAN

[W6LKB]

Thank you for responding to me. I will definitely fire up the VNA and tune everything. Hopefully that will suggest a solution.

I was just trying the easy route based on the couple of suggestions of removing L11 turns to increase power. I played with the capacitance because my board has 68pf in C10/1 but in your table for the Alternative Bands you recommend 128pf for that.

Thanks again for designing such an amazing unit.

[W6LKB]

Following your tuning approach with the VNA solved my 20M issue. Now getting over 3W at 13.8v with over 60% efficiency. Other bands improved. All good.

Thanks again.