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I am researching a low-power-on-one-band symptom on my High Band QDX, Succinctly, the power out was measured into a dummy load via a WM-2 and the rig was powered with a 5AH SLA bucked down to 12.0 VDC. Results below:

??? 20m ~6.0W 0.70A
??? 17m? 5.0W 0.66A
??? 15m ~6.0W 0.74A
??? 12m ~4.3W 0.66A
??? 10m? 2.0W 0.59A

I then did an RF filter sweep of the rig using PuTTY and got the images attached below. Here are my questions:

(1) I checked and compressed and loosened the turns on L4 and L10 to little or no effect on the sweep of 11m or 10m.

(2) To me, 20m looks like crap yet the rig puts out a healthy >5W on that band.

(3) The rest of them looks sort of OK.

(4) The 11M/10M looks great and clearly (to me) does not look like the LPF is causing the low power condition.?? ?

(5) Sorry for the ignorant question, but what do the filter sweeps show to all the trained eyes out there?

I have consulted the LY2H and EX0AA comments on the one-band-low-power matter and am still sorting through the group's anecdotal comments and other resources. Like LY2H, who could live with 3 watts on 10 meters, I could as well -- just not the one watt that my rig outputs on a 10m antenna. Also, I mainly want to get "some steerage" on how to utilize the tools and techniques to solve the problem.

Thanks in advance,??
--
William, k6whp
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"Cheer up, things could get worse. So I cheered up and things got worse."

Hi William,

The RF sweeps combine the LPF and the BPF (L12 and one of the selected capacitors).? The most impact is from the BPF.? If the LPF is correctly built, it will be significantly above the operating frequency.? With that said, I do not use the RF sweeps to tune the LPF.? That is done by compressing or expanding the turns on the two toroid inductors in the filters.? Both can impact the output power, though, for me, the most impact was with the L2, L3, or L4 toroids.

Hans has a video on tuning a QCX LPF that can apply to the QDX.? The QCX has more toroids, but the principle is the same.


73
Evan
AC9TU

Evan,

Thank you for your reply. I went back to carefully review my work as well as LY2H's video covering this subject..



After carefully inspecting L12, I believe it is one turn short between "17t" and "End (20t)". I am not sure that is apparent from the pictures I posted below but using magnifying eye glasses and a harsh light, it goes to the last turn being omitted. In testing per the video cited (scrunching L4 and L10's turns closer together), I was able to get the output up to 2-1/2 watts but that only made me more convinced -- as you said -- that the BPF is the major factor in this situation.

Interestingly, I will have to "work up the courage" to extract L12, rewind, and replace it. The other bands -- 20m through 12m -- put out a robust 4-6 watts* and I am loathe to turn the whole built rig into lunch meat for the sake of 10m. I may yet gain the nerve to do so, but my recent experience on 20m and 15m compels me to manufacture a 12m and 17m vertical and see what can I see.

..all of that said, I marvel at the technology and research that went into designing the radio, how Hans has brought fire from the Gods like Prometheus of old, and how wonderfully abundant this group is with knowledgeable hams as yourself to provide support.

Thank you again.
--
William, k6whp
--------------------
"Cheer up, things could get worse. So I cheered up and things got worse."

*which will be throttled back to about 5 watts by lowering the input voltage.

William,

I count 20 turns on both of the toroid pictures.? The difference is on the 14th turn.? I count 15 turns to what should be the 14th turn and then only 2 turns between 17 and 20 on the second picture.

L12 will not impact the QDX output.? For 10 meters on a high band QDX, that is L4 and L10.? Have you tried squeezing or expanding those toroid windings?

73
Evan
AC9TU

In testing per the video cited (scrunching L4 and L10's turns closer together), I was able to get the output up to 2-1/2 watts but that only made me more convinced -- as you said -- that the BPF is the major factor in this situation.

Yes, I did.? Perhaps my surmise above was incorrect. As I said before, I'm reluctant to butcher the radio when it operates perfectly well on 20m through 12m so far as power out is concerned -- and I am fine with 2W on 10m for the moment. I have a Low Band QDX coming and I will be more circumspect about winding L12 and the LPF coils on that.?

Dunno.
--
William, k6whp
--------------------
"Cheer up, things could get worse. So I cheered up and things got worse."