QCX+ adjustement and alignment
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Checking my newly built 20M band QCX+ I found the following facts:
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On a 50 Ohm dummy load
- with a 13.5V DC supply I only get around 3 Watt output;
- 8.7 Peak BPF looks OK;
- 8.8 I-Q Bal 8.9 Phase Lo and 8.10 Phase Hi show high minimum values;
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After connecting my AlexLoop magnetic antenna I get only noise where I should ear some CW and around 14,074 some FT8 noise. I went to 15,000 MHz to ear the hour signal but nothing except a continuous signal on 15,005MHz.
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Para 7.3 page 130 of the manual writes: "Your results may vary depending on your Low Pass Filter inductor construction! If the cut-off frequency becomes too low, then you start to get attenuation at the operating frequency. In this case you can remove one turn or two from each toroid." As the LPF work both in Rx and TX I understand that if their cut-off frequency is too low I loose Rx sensitivity and TX output power.
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Do you think I should actually start by removing one turn on L1, L2 and L3? I guess it would just raise a little the cut-off frequency without increasing the 2nd and 3rd harmonics?
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73 - Pierre - FK8IH |
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Hi Pierre. I also recommend watching that video, especially the part where Hans shows you it is not necessary to clean out the holes. The toroid leads can be soldered to the top side of the board and save a lot of board damage potential, especially if you are making several adjustments to the turns counts. Also, the method is good for any?band, but it is different in the number of turns removed or added, depending on the band. In about 58 twenty-meter versions of the QCX that I have worked on, almost without exception I've had to remove one or two turns max from L3 and none from L2 or L1. As Hans mentions, spread the turns on L3 first. If you see an increase in power out, spread them some more. If power out is still increasing when you have spread them as far as they will go, then remove one turn and continue. When you have reached a peak in power output adjusting L3, then squeeze the turns in L2. If power increases, squeeze them some more to reach a peak. Then, finally spread the turns of L1 for maybe a slight improvement.? Since you are already at 3 watts then you probably won't have to remove more than one turn at the most from L3. Lastly, if at any point you see a decrease in power just take the last turns you were squeezing or spreading and adjust them in the other direction. Don't try to squeeze out every possible milliwatt. When you get to 5 watts at 13.8v input, you are at a really good spot. It is always tempting and sometimes possible to get 6-7 watts output but it isn't healthy for the BS-170s and makes almost no noticeable difference on the other end of the path. Good luck ... 73 .. .Ron On Tue, May 27, 2025 at 3:48?AM Evan Hand via <elhandjr=[email protected]> wrote:
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Thanks to Evan and Ronald and obviously to Hans for his YouTube.
I checked again my QCX+ (built with 1N5819 diode which substracts around 0.4V to the DC supply) on 14,020 kHz: 1. With 12V DC suplly I got 2.33 Watt, after removing 1 turn of L3 I got 3 Watt and after removing 2 turns of L3 I got 4.11 Watt.
2. With 13.5V DC supply I have now 5.3 Watt.
3. With 15V DC supply I have now 6.33 Watt.
WONDERFUL? (I tested 15V because I plan to use it in SOTA with 4 LiFePO4 batteries which give around 14.3V fully charged.)
I took this opportunity to end the check with 8.7-8.8-8.8 and 8.10 according to the YouTube recommendations. I still have no GPS but I plan to build one QLG2 unit.
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I measured the output power with a product designed by another talented British OM: M0BMN Paul Webb, producer of Kanga kits and I used his dummy load-power checker
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73 - Pierre - FK8IH
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Pierre - FK8IH
Ronald Taylor