over 10W and 99.99% eff

[VA3KTJ]

I bought a kit from Amazon and assembled. Everything seems to be fine. Even with random wire antenna, I could get pretty good RX at most bands.
I have measured SWR and power with my meter and the SWR was not good because the antenna was not set up properly. I would do the tuning soon. The power with 12V was about 2~4 W which makes sense with poor SWR.
I tried to get familiar with the menu and set the display 1.13 SWR Meter with the option, PWR-EFF, and it shows the power over 10W, 10~14+W, and the efficiency was 99.99% (no change) at all bands.
I took a close look at the PCB where I soldered, and removed the SMA antenna connector and see if there is anything wrong with the soldering, but couldn't find anything. See attached pictures.
Can anyone help me to fix this problem?
Thanks,
VA3KTJ

[KE0QQQ]

Congrats on the build, tiny little things .. eh?

I did a search for SWR and went to the last page and from the beginning of time to get the reason why you see crazy numbers

https://forum.dl2man.de/viewtopic.php?p ... +SWR#p1346

Test with a dummy load and known good connections at USB power till you see good numbers
Even then, dont hit the big power till you know what you got

The radio does not like open connections, freaks it out

Is it the 2 coils for output, is it the SMA solder connection

Is it the little cable letting the center wire creep back because of a winnie crimp < me recently

Does it receive ?

[VA3KTJ]

@KE0QQQ, thank you for your reply.
As you suggested, I tested with the USB power (from my PC, so it's max. current is 500mA) and 50ohm dummy load. All band shows around 5Watts, but the efficiency is still 99.99%.
I also briefly tested with 12V and the dummy load, and the power displayed over 12W and the eff. is 99.99%.
Does this indicate something?
Thank you.
de VA3KTJ

[KE0QQQ]

Just the vague idea of an open circuit, somewhere between the 2 black coils and the SMA.

Does it pick up FT8 on any bands ? A good marker to test against

[s57l]

Check t1 and t2 for correct winding and soldering.

[VA3KTJ]

Thank you for your replies, KE0QQQ and s57I.
I have double checked all the solder joints, SMA connector, and any shorts. Nothing found.
I guess the high power is due to the un-tuned antenna. I have no good antenna at this moment. With the USB power, the power shows 0.8W. But no matter what power source I used, and either with an antenna or dummy load, the efficiency always shows 99.99%.
How is the efficiency calculated? Is the U1 (INA219) monitors current and the current reading sent to the micro through I2C and calculate the efficiency? Could U1 be damaged (or defected??) or is there any other component(s) I need to check?
RX is fine and TX at 7MHz works fine (checked with another QRP, Forty 9er). Only thing bothers me is the displayed efficiency.
By the way, I love the design and its compactness of (tr)uSDX. Cheers!!!

de VA3KTJ

[adam_b]

Have you checked here?

https://forum.dl2man.de/viewtopic.php?t=1586

I had the same problem.
BTW it is best to check it on an dummy load.

[VA3KTJ]

Hi Adam,

Yes, I have seen your post when I search the forum to find similar issues.
That's why I have desolder the SMA connector (I assumed you meant the SMA antenna connector by 'goldpin connector') and clean the PCB around the connector and solder the connector back. But it didn't solve my issue.
Just now, I read your post again and measured the voltage on the RVS pin and it was 0.7-0.9V. And then I disconnected power and separated the RF board and measured the resistance between the 12V and RVS pins and it didn't show any resistance. With the two boards connected, the resistance was about 3.5Mohm.
What else can I try......
Thanks.

[adam_b]

Hi,

Goldpin - I meant the connector between main board and RF board. If on the RVS pin it was 0.7-0.9V at 99% you have the same thing as me. Try desoldering the connector on the RF PCB first, thoroughly clean the PCB at the connector on both sides of the RF PCB. Re-solder the connector and check for voltage. If it still persists, do the same with the connector on the main PCB. On RVS pin the voltage may be several millivolts.

[VA3KTJ]

Ah, ok. I will try that.
Thank you, Adam.

[adam_b]

The RVS pin is located near the 12V pin and there is a risk of leakage.
It is also worth cleaning the goldpin connector between the pins, especially on the PCB side, after desoldering it.

[VA3KTJ]

Before removing the header pins, cleaning and resoldering, I did a quick test. With a USB power (from PC, so 500mA max, 5V), with ONLY the main board, when I press the PTT button, it shows over 10W and 99.99%. Is this correct without the RF board?

[adam_b]

The question is what is the DC voltage on the RVS pin now? Is there any voltage on the 12V pin?
The diagram shows that there will be +5V there. If there is dirt under the header pins on the main PCB, it is possible that the RVS pin will have voltage from the 12V pin, now there will be 5V on the 12V pin when you supply from USB only.

As I wrote earlier, the voltage on the RVS pin can be several mV, but no more, a higher voltage value is information for the uC that there is RF power.

[VA3KTJ]

Hi Adam,
Thank you for your reply.
Now I removed the header from the main board and cleaned (nothing visibly wrong or dust was found).
And then as you said, with the USB only powered and RF board not connected (obviously can't connect it without the header), the RVS pin's voltage is less than 50mV. I was holding the multimeter probe a little longer (a few seconds) and found the voltage gradually dropped to 0V.
The 12V pin measures 5V which is correct with the USB power.
Another interesting thing is right after I connect the USB cable, if I press the PTT, the power is 0W and the efficiency is nan%. That's correct response I think because there is no feedback from the RF board. But if I hold the PTT a little longer (a few - several seconds), it started showing the power as about 0.xxW and the efficiency as 99.99%.
Now I tried to measure the RVS voltage, and noticed the power and efficiency changed to 0W and nan% as soon as I connect the multimeter probes.
It looks like the PTT charges a capacitor (no idea which) and makes the RVS pin goes high potential. With the multimeter probe, somehow it discharges.
It's getting more interesting.

[adam_b]

Hi,

also clean the connector (header) between the pins well before re-soldering. If, at approximately 0V on RVS, the power reading is 0W, it means that the uC is operational - port of Atmega for RVS power measurement.
You can also do a test by shorting RVS to GND, the voltage will drop to 0V and you can check whether the power is 0W.
It is possible that a mainboard without an RF board connected will show some power. There is a 10nF capacitor on the RF board connected to GND from the RVS line, which loads this line.
Clean the connectors thoroughly as I wrote, reassemble everything and I believe it will be fine .

[VA3KTJ]

Hi Adam,
Thank you so much for your effort to figure out my problems.
I learned a lot from your suggested troubleshooting ideas. I have checked the RVS, FWD pins and all the components around the SWR circuitry comparing to the schematics, but still no clue.
I'm thinking to remove T1 and T2 and check the coil and the PCB without them. That might give me some hints, I hope.
Thank you again for all your help, Adam!!

[adam_b]

Good luck and I hope you manage to find the cause. Make sure that there is no voltage on the RVS without transmitting, or a very low voltage in mV, then you can look further in the SWR bridge - T1 and T2.
If you find the reason, write it here on the forum, I'm curious what it could be.
I struggled with such a case myself and the cause was dirt under the connector as I described to you.
Best 73!

[VA3KTJ]

I think I found the answer.
I have cleaned header pins, antenna connector, and PCB multiple times, but that didn't help at all, so tried to search the forum with various keywords again and found a post https://forum.dl2man.de/viewtopic.php?p ... 228b#p1688.
I followed wa2t's solution, replacing C7 and C8 with 1M resistors and change R5 and R6 to 1k. Now I get reasonable power and efficiency and SWR. The uC, ATmega328p, which is also used for the Arduino seems to require certain impedance inputs for the ADC. I don't know exactly how it fixed the wrong PWR and efficiency readings, but I'm happy that I found I didn't damage anything and found the solution.
But I don't understand why only some of the (tr)uSDX behave this way.
Hope this can help someone who has similar problems.
Cheers!