开云体育

Mark,
For playing with the LM386 circuit: I pulled the LM386 and factory socket.? Replaced factory socket with a machine pin socket then built a daughter card that plugs into that machine socket.
I went the route of adjustable audio gain.? No problems observed at low volume with a lower gain.? Even with the factory TFT, cable routing must also be tended.

Rgds,
Gary

Raj had a suggestion for another issue with noise.? Check this link:
/g/BITX20/message/98750

Adding the resistor between the junction of the volume control and the LSR to the input of the LM386 would mean modifying the board as the volume control is mounted on the mainboard.

73
Evan
AC9TU

Hi All,

I am curious: with the new MOD #2 changing a significant amount of circuitry, is the TX signal still hitting the ULN2003A (U4)?? I ask because I made a rather simple addition to my radio by adding an LED and resistor across the coil of K9 to indicate when the radio is in transmit mode.? I did this because in an automated mode, WSJT-X, when the screen normally blanks, there is no indication that the radio is ON or in transmit mode.? With this LED (and a similar PWR LED to indicate when the radio is powered on), from across the room I can see if the set is on and operating.? It seems like U4 is still in circuit and TX is still feeding input pin 15 (pin 5 out) and it will still work, but I thought I'd ask.

Thanks, Scott?

Raj,

Did not know that! Thanks. Will make that mod when I start testing the Vol hi input for the s-meter.

73
Mark

--
AJ6CU
KD8CEC 2.0, Nextion Screens,? and open source uBITX Raduino boards for Arduino IOT, BLE, RP2040, Teensy 4.0, and Raspberry Pi Pico
https://github.com/aj6cu

Try shielding the LED and photo-resistor from extraneous light.? Once in the active region it may be picking up noise from CFL lamps for example, or LED house lighting.

On a side note, the circuit has positive feedback with the cold end of C3 tied to the emitter resistor.? Does it clip peaks or act like a noise blanker and blank the signal completely for the 6.3uf / 4.7k time constant?? Does it sound better with the cold end of C3 tied to ground instead?

Hi All,

This is the second issue I’ve seen since mod kits have been arriving. ?I’ve not received my kit yet but I suspect it will arrive soon. ?My thinking is to hold off on installing the mod until Anthony and Evan’s problems are resolved or am I over reacting?

Scott

I meant when you activate the LED.
Hadn't had my morning espresso yet.
Howard

Nice construction job.

I've installed several of these AVCs and haven't had that experience. ?Given that it happens when you activate the AVC, I wonder if it could be the location or routing of the wiring from the LED to the control. ?It might be a good idea to use shielded cable, or maybe you have; I haven't spent enough time with you photos yet to figure out what's what completely. ?The LCD is one possible source of interference.
73 Howard K4LXY

I should be getting the upgrade kit #2 tomorrow (according to the postal service). I’ve already removed many of the SMD parts—if you have a hot air resoldering station it makes it much easier. I can’t wait to get the upgrade finished, and thank you Ashhar and others who have been so helpful. I have as much fun doing this as operating.
One concern, though: AC9TU and K3NG have noted some anomalies in the behavior of the rig after doing the upgrade, and Ashhar alluded to a software upgrade that would also be helpful. What is the current status of the upgrade project, and is it appropriate to proceed with the upgrade now or should I wait for further information? Has anyone else completed the upgrade, and what has been your experience?

Mark,

The LM386 tends to get unstable when volume is turned all the way down.

Disconnect the center lead of volume pot and add a 1-10K any resistor between

the volume center and the LM386 input.

Happy new year!

Raj

Thank you, Allison.? I will try to work out the issue from these.

73
Evan
AC9TU

Until the docs are improved what I have may match or are at least close.

NOTE sBitx_main_v2.pdf shows diode switched LPF. NOt implements but the RX/TX
switch may match the little board or be close.? The other was an earlier proposed
and again likely close but not exact.

That may help.
?
--
Allison
------------------
Please use the forum, offline and private will go to bit bucket.

Some background:
I applied both upgrade/modification kits to my sBitx.? This was after having blown the finals and the transmitter keying section (Q9 and Q10 with the added 2n7000) after the first software-based T/R fix.? I replaced the transistors and added the mods.? I also updated the software with a git pull on my second Raspberry Pi 4.? It started up without any apparent issue.? I was connected to a dummy load, so I did not test the receiver, though it did appear to be working with the dummy load.? I was able to set the bias per the upgrade instructions.? I turned it off (I forgot to shut down the software first) and the next day went back to continue working on it.

The power was first measured at 15 watts, then dropped to 2.5 watts.? It started to draw an excessive current, and I could not turn off the transmitter.? Now anytime I key the transmitter, I get the 2.5 watts out, high current draw, and have to power off to stop it.?

Suggestions on where to look are welcomed.? Since it seems to start in receive mode OK, I assume there is an issue with the T/R board.

What I need are the schematics of the T/R board.? The main board schematics in the upgrade document do not have the details of the T/R board.? It is hard to diagnose without the schematics.?

Any help is appreciated.
73
Evan
AC9TU

Hi All

I've had an uBITX v6 for a couple of years now, at first I used it without modifications, but after a while I started modding it.

1) Increased mic gain to avoid shouting at the microphone
2) Allison KB1GMX's mod for driver and pre-driver stages to enable more power at higher bands.
3) Changed stock heat sinks for bigger ones

Also, In the last months, I have put together a small board to enable some extra capabilities.

1. CW audio filter using Op Amps
2. LM567 tone detector to center CW signals in the filter's passband
3. VK3YE's automatic volume control using LED/LDR

I tested the board and then mounted it inside the uBITX using a 3D printed support. I've added to the front panel a LED for the tone detection and two switches to enable/disable CW filter, and to enable/disable AVC.



I tested the tone detector and CW filter, and they are working as expected.
The AVC can attenuate strong signals, when a weak signal is present, I don't perceive any audio distortion. However, when I receive a strong signal, the LED shines and the attenuation kicks in.
The signal is attenuated, but a high frequency noise is generated, like a whistle or hissing sound.

I tried increasing capacitor sizes (C2 and C3 in schematic) without luck, I also moved the wires to check if there is some sort of coupling, but that didn't solve anything.
I sense the signal from VOL-H and then LDR is connected in parallel with VOL-M. The LDR has 200k ohms dark resistance and drops to a few ohms when the LED is at max strength.

After some tests, the noise also appears if I attenuate the signal illuminating the LDR using a flashlight, so It doesn't seem to be related to the LED circuit. Any clues or suggestions? Maybe I need to try a different photo resistor?


Any suggestions for this issue or for the other mods are welcome.
Thanks
LU2HES

I have also found that the location of the cable harness to the mainboard and Raduino measures a lot. If I ran them high, immediately behind the Nextion, even with volume turned to minimum, I would hear a loud screech on boot. (Interestingly, if I turned the volume up a couple notches, the screech would go away. When i tucked the wiring harness down below the Nextion, all was good. I haven't done a lot of TX on the uBITX, so cant confirm that your TX lockup will not happen.

73
Mark

--
AJ6CU
KD8CEC 2.0, Nextion Screens,? and open source uBITX Raduino boards for Arduino IOT, BLE, RP2040, Teensy 4.0, and Raspberry Pi Pico
https://github.com/aj6cu

My notes on how my upgrade went, some suggestions for potentially making it easier, including links to Farhan's excellent instructions for the TR upgrade, and link for the switching regulator upgrade (which I hadn't yet done) are:



73,
Gordon KX4Z

Got both the switching regulator and the T/R switch upgrades done.? ?Discovered a few items along the way.? ?
Broke the pad on the switching regulator output while reassembling -- no power to the PI.? ?Ran the Pi from separate supply until dissassembled the entire thing AGAIN and found the broken connection, effected a repair.? ?First time I have pushed the PTT on this fantastic rig.? ?I had great fun tuning the lower and upper filter points while listening to CW on 80 meters!? ?
Soon I'll list some hints and notes on goofs I made, photos.? ?
The upgrade two instructions:? ?
I would have to admit considerable trepidation on the SMD parts!!!? ? Delighted that it is all back together and apparently working.? ?Fantastic learning tool.
Gordon KX4Z

Interesting. I had a similar problem with my uBitx v6 and a Nextion screen. Mine is 5”, and the upper bands would lock up in transmit with no side tone. It would stop only by cycling the power. I must have fixed it by simply moving around some of the cables because it resolved without doing anything else, and I never found the cause. Along similar lines I solved the Nextion noise whine from suggestions here. It’s audible even when the audio is turned way down. Apparently it’s from the Nextion backlight which is minimized by increasing the brightness to 100% but is still annoying. The noise was completely eliminated by putting a 2.5 mH choke in series with the red Vcc power line to the Nextion. I used a FT-114-43 toroid. 70 turns of #22 gauge wire was recommended but I was able to wind a few more turns than that, and my meter showed 3.5 mH. I also put a small 1000 μF 16 V electrolytic across to ground for good measure. I also used RG178 in the audio lines.