开云体育

In short:
Reception is fine, HF-path and audio from the speaker are ok.
When sending, there seem to be no microphone input and no "audio mod" output to/from the audio codec.
- Which signal is displayed in the scope at the SBITX web interface? Is it the signal generated in the software? Is it the microphone input? Or is it even a demodulated "feedback" from "audio demod"?
- Which loopback device is used for the microphone and "audio mod"? I would like to test and measure this with Audacity and my scope.
- Has anyone else had this problem and solved it?

Long:
I received my SBITXv2 (complete and calibrated kit) on tuesday, serial 0270.
Since I wanted to test the device first at the dummy load this weekend, before I make operation with it, I tested only the reception the first days.
This works very well, without problems, nice interface, even on the smartphone, great work! (I really like the TRX and all its capabilities)
At some point I did an update of the debian in addition to the sbitx software, more or less out of habit. That also ran without problems.

Now I wanted to test the device yesterday for the first time on the SWR meter and a dummy load, first carefully with Drive=1..10...30...60...100.
But unfortunately? the device does not generate any transmit power. Never.
CW, SSB, FT8, TwoTone, on each band: 0 Watt output power. The current consumption increases only 2-300mA.
Since there was a test report on the device and I bought the already calibrated complete device, I assumed that I can put it into operation immediately. If you have more DIY projects on the table than free time in your calendar, you don't really want an additional tinkering object on the table. So this is now a disappointing result.

When sending with the internal and the external microphone, nothing is displayed in the NF scope, except a flat yellow line.
It seems that the microphone input is not working. But with CW there is also no transmitting power, so this is not only a problem with the audio input.


Step 1 - new image for the SD card:
Now I thought that I might have overwritten any settings or dependencies due to the debian update.
After I found a link to the SD card image, download and wrote it to the SD card (took a while), I realized that it was the old image from the SBITx-DE.
Since the download is not small, extracting and writing to the card also takes a long time, this hint in the post would have been nice...
Through another post in the SBITX group, I found the correct image for the V2, downloaded and unpacked.
The missing file extension can be solved quickly. But the image does not fit to the card that is delivered and installed by default in the SBITXv2? Going nuts... And no, buying a bigger card is of course not a real option.
With another hint in this group I found out how to shrink the image with "pishrink". That also took another long time, but I could now write the image to the card.
After 3 hours (just for the right SD-Image) the device finally booted with a new SD image.
Thanks to the community!

The V2-SD-Image is now 12GB and can be found here as 2.9 GB rar-file:
https://drive.google.com/file/d/1fzAxP5e3n19EEBIejtBU7ZmWDniRYUGA/view?usp=sharing
(Partition resizes to full card size at 1st boot)

Unfortunately, this did not solve my problem. :/


Step 2 - Measurements in the device
After I found out that "sbitx_main.pdf" didn't fit to the actual device, I came across the hint that all schematics for the SBITXv2 can be found in "sbitxv2_circuit.pdf". Here a clearer naming would be helpful, but again: Thanks to the hint in the community ;)
I bought the SBITXv2 also because all schematics are available and the board can also be easily understood and repaired by myself. I had little pain with opening the new device and however, this should not be usual for a device that is considered complete, even at this price. But ok, needs to be done...

The PA transistors were unsurprisingly (still) fine, as the unit didn't short out either.
The TX circuit around Q9, Q29 and Q28 also worked as expected.
I then tried to figure out where the RF signal was missing, tested with CW and Drive=100, in this order:
Antenna output, PA low pass input (C205/C206/C202), PA input (L80+L81, bias is also ok), driver input (C5).
No signal found.

Testing the low pass filter L16+L18+L19+L20+L21, I thought I had found the signal. At first L19 seemed to have an interruption, but as it turned out, the winding of the coil was pressed against the capacitor. A slight movement and a second later my power supply was reading 20A and the PA was toast. Going nuts again...
What I now really like about the SBITXv2 is that you can easily swap out the power amp. Unscrew the heatsink from the board, desolder, solder in, 10min work. Great! And thanks for the delivered spare FETs :)
The bias is also easy to pre-set to 2-300mA, especially since currently no RF signal goes through the PA. A little higher I turn maybe, as soon as a RF signal arrives there and I can measure that better.

Now I can't reliably measure the signal path through the mixers and the quartz filter with my scope. So I have skipped these stages.
In the path between "Audio Mod" and the first mixer there is no signal at L22 either. At "Audio-Demod" I can measure amplified noise behind Q8 (but not the sine tone when sending from CW.).
Because the audio codec sits under the Raspi I can't measure further.
Since the solder joints on the codec were not cleanly soldered, I reworked them, but without success (as expected).
What I measured was the input level from the microphone around QD1(C)/RD15, which is ok. ?
The same applies to the speaker amplifier, which is also working.
As said, the reception works fine. It seems to be a problem somewhere in the transmitting paths, probably even at the audio codec.

Now I need some help, because I just can't get any further. For this I have a few questions:

- Which signal is displayed in the scope at the SBITX web interface? Is it the signal generated in the software? Is it the microphone input? Or is it even a demodulated "feedback" from "audio demod"?

- Which loopback device is used for the microphone and "audio mod"? I would like to test and measure this with Audacity and my scope.

- Has anyone else had this problem and could solve it?

Thanks a lot for your help!
Daniel DL2AB

(Since I was perhaps somewhat drastic with my remarks:
I like the device and I really want to get it working. This is also not to be understood as a fundamental criticism of the project, although I would like to see some improvements in the documentation and on the device. I am mainly disappointed about the fact that I have now received a not quite inexpensive device without transmitting function - even if the test protocol says something different. However, as a technician, I know that this happens from time to time.
I should also add that we have already set up 12 uBitX (v5+v6) at our radio meeting and were able to solve all problems somehow. So I am confident that I will be able to use it on the bands soon, even if this now needs more work than I thought. But at this time I need some help from you :)

Hi Daniel,

To start, I am a DE owner, not a v2 owner.

With the above understanding, my first comment is that if you did not save the files in the data folder under the sbitx folder (/home/pi/data), you have lost the calibration information, which is what is adjusted when doing calibrations.

Even with the hw_settings.ini file lost, you can copy the default_hw_setting.ini to hw_settings.ini to get started again.? All of the transmissions will be much lower than the calibrated setup.? At some point, you will need to do the calibration steps to get back the power and SWR settings.

As far as the transmission problems, all modes having the issue point to a problem with the codec output to the first mixer and onto the PA.? The output of the codec can be measured at the C91 C93 junction.? You should be able to measure an approximately 48kHz signal at that location in both Receive and Transmit modes.? I would use CW as the test mode.

If the signal is not there on transmit, check pin 2 of Q6 to see if the 2n7002 MOSFET switch may be the issue.? Verify that the gate of Q6 is at 3.3 volts.? Also, verify that the 48kHZ signal is at the source of Q6.

Use the same gate check to verify that Q5 is turning on.? I would then check Q3 to verify that it is in an active state (approximately .6 volts Base to Emitter) when transmitting.

One of the final failures on my DE took out one of the 1n4007 diodes used to switch between TX and RX.? It also took out the Q22 equivalent (Q3 on the DE TR upgrade).? The receiver was not working for that issue.

What is the current state of the receiver?? Is it working?

I would never recommend testing at 100% drive level.? It is too easy to burn out the driver or PA stages even if there is no output from the finals.

73
Evan
AC9TU

Did you run txcal? Otherwise it doesn't work.

Bitte txcal ausführen mit dummy load dran. Und wenn m?glich strombegrenzung. Mehr wie 10a dürfen nicht.?

Thanks Evan and Andi for your hints :)

First I tried Evans tipps. Reception was ok, but I will remember to check the reception path when I blow up the finals next time.
48kHz-"spikes" found, but Q6(2) without NF. 3.3V was present at Q6-Gate while TX, same at Q5 and Q3.

Than I tried the hint from Andi.

I didn't know that I need to do the "txcall" for a proper output. I thought this is just for meter calibration and just needs to be done for later adjustment.
I assumed that some (small) signal must come out of the codec in any case. But there I was wrong.

After txcal and metercal the SBITXv2 worked fine on the dummyload. \o/ YEAH! \o/
I have just tested the mike and it was fine too - not perfect, but more than good enough.
I only have minor issues with the meter calibration but I think this is not a real problem.
The only "major" issue now (after playing around for half an hour): I "calibrated" the gain, because I got "only" 30W.
I'm a little embarrassed now, but I blew the PA again while adjusting. I had probably still set the current limit too high (I'm a goofball).
But this may sound strange: It may be that I have never been so glad to have blown any PA ^^
Fortunately, the new transistors have already been shipped and this is now solved really quickly.

You have helped me a lot, big thanks!

Hi Daniel, Glad it worked. Too bad you wanted too much. The new Sbitx are much more conservative. 30W or 35W and end. This is also ok to have some buffer for mismatch. The problem, metercal cannot be set to 40w. Just leave the value in the ini at 100 and live with the fact that it shows a bit too much. I also tried pulling that up to 40W. But since the bias current has no thermal regulation, I ended it at 10A and prefer to leave it as it is.

Hi Andi,

yes, that was maybe the reason I blew the finals the last time. 40W were reached, without problem, but no longer than 30-40s...?
Yesterday i received the new transistors and replaced them. After calibration I checked the harmonics and they are ok too (~-45dB at 80m, -50 to -55dB at 40m).
Now the PA is at 32-35W at 40m (~9.5A), ~13W at 10m.?That is absolutely ok, more than a IC-705 or X6100 ^^ - and it doesn't really matter.
I was wondering about the calibration too. With Drive=100 it is displaying 6W more than measured and can't be calibrated. Maybe this can be solved later or I will look for this, but it is not as important as the SWR (which is ok compared to my ext. SWR-Meter).
The SBITX is running now and it is great! I have learned the circuits (kind of) and it produces more than enough output power for my needs. Mike is not distorted, Audio Quality seems to be ok.?
LiFePo4-Battery (12.V/6Ah, Eremit) is ordered and should perfectly fit to the back of the SBITX (together with a 80mm-fan).?

At the weekend I will test the SBITX at the antenna with my new portable setup.

Thank you again for the right hint! :)

Daniel DL2AB

?

?

?