September 2022 – sBitx.net

sBitx Basic Kit Assembly Notes

Ken, N2VIP

Here are some photos/steps I took to assemble my sBitx “kit” (complete minus RPi 4 and Raspberry Official 7″ Display).

A reminder, here’s what’s included:

1) remove the front and top panel, being careful to not damage the wires attached to them. There is no reason to remove the back or bottom. Disconnect the speaker lead from the circuit board and put the top aside.

2) remove the back plate from the front panel, re-attach the back plate to the front panel. Connect the red lead included with the display to the 5v connection on the display board, the black lead to the GND connection. Do not attach the display ribbon cable (yet – it turns out it’s easier to attach the ribbon cable to the display later, trust me.)

3) Prepare the RPi 4 – insert the MicroSD card in the reader and attach the Display ribbon cable to the display connector on the RPi 4, the silver leads face “up” the blue tape is down, against the black ‘wedge’. If you are not familiar with these connectors, there is a wedge that lies against the circuit board – pull it out a tiny amount, don’t force it) the ribbon cable should just slide right in, then slide the ‘wedge’ into the connector.

4) Mount the RPi 4 to the digital board, being sure the 40 pins on the are correctly inserted into the socket (tip – if you can’t see any pins on top of the black connector, and you don’t feel any pins on the bottom of the black connector, you’ve got it right). The screw holes on the RPi 4 won’t match the standoffs on the digital board if the pins are not correct. (Again, the display ribbon cable should be installed before you secure the RPi 4)

5) Lean the front panel against the front of the chassis, twist (!) the display ribbon cable then insert it into the display connector, silver leads facing away from the circuit board, blue tape against display PCB.

Secure the front panel to the radio with the 4 screws you previously removed.

6) Connect the red lead from the display board to the lower power connector on the component side of the digital board, the black lead from the display board to the top pin as shown:

7) Re-attach the speaker connector to the three-pin connector on the digital board (it only attaches one way), then seat the top of the case back on top and secure it with the 4 screws you previously removed.

NOTE: HF Signals assembly instructions instruct you to use the included two pin jumper cable, soldering the wires to the pins on the display board, but the supplied jumpers that came with the display (red/black/yellow/green, female-female, about 7-8″ long) are just fine and should be secure for most users.

There were some leftover parts:

8) So then I applied 12v (13.8v) DC and my unit powered up!

Starting the sBitx application, you see this:

The wifi ‘burp’ is quite obvious, I know turning off wifi will stop that, but now to grab my mic from my uBitx and hook it up to an antenna.

Thanks to everyone at HF Signals, I’m very pleased with this build.

I hope these instructions help others decide if they want to buy a “kit” or “assembled” sBitx.

How to set the bias

Siegfried Jackstien, DG9BFC

Set both the POTS to minimum current
Select Mode as USB. Reduce the MIC to zero.
Press the PTT.
Without speaking into the microphone, carefully increase the DRIVE_BIAS POT until the current increases by 200 mA. Note the current.
Keeping the PTT on the microphone pressed, now increase the PA_BIAS POT until the current increases by another 200 mA.
Release the PTT.

Eliminating Periodic Noise in the Speaker (Developer Edition)

Ashhar Farhan, VU2ESE

The LM380 audio amplifier is picking up the Wifi RF and it results in a noise that repeats every 8 seconds of so as a series of quick pulses.

The noise is not present if you use earphones as they bypass the LM380 audio amplifier.

The current solution is to just turn off the WiFi and use Ethernet instead for Internet.

Corrupted sBitx – How to reset the settings.ini

Anthony Good

Before you replace files, try deleting (or renaming) your settings file, /home/pi/sbitx/data/user_settings.ini. I have had it several times where upon restart of the app or restart of the Pi, something goes wonky and deleting the settings file fixes it. I haven’t gotten to the bottom of it yet.

If you need to toss a hand grenade, I would do the following (First open a terminal with Ctrl-Alt-T and then type:)

cd /home/pi
mv ./sbitx ./sbitx.old
git clone https://github.com/afarhan/sbitx.git
cd ./sbitx
./build sbitx
./sbitx

Upgrading to switching regulator (Development Edition)

From Anthony Good, K3NG, Anil Rayporula, VU2DXA

The very early sBitx (Developer Edition) were shipped with a linear regulator, the LM338 to drop the voltage down from 13.8V power supply to the 5V needed by the Raspberry Pi and other digital circuitry. This often led to heating issues. An upgrade kit was shipped to these users. These are the instructions to install it properly.

The new regulator looks like this:

1. Take off the top panel and disconnect the speaker. Lay this aside.

2. Disconnect the white ribbon cable going from the Pi to the touch screen display. There are little black tabs on each side of the connector on the display unit that need to pop straight out in the direction of the ribbon cable to release the ribbon cable.

3. Disconnect the brown and black wire (touch display power) from the digital board.

4. Remove the gray ribbon cable out of the digital board by pulling the gray ribbon straight backwards.

5. Loosen the two nuts on the right side holding the metal bracket that the Pi and the digital board is mount to. Do not take the nuts entirely off.

6. Pull the Pi and digital board assembly straight up to remove and set aside.

7. Remove the four screws holding the main board to the chassis

8. Disconnect the two red wires from the power switch on the back panel

9. Remove screws on the four back corners of the outside of the chassis to remove the back panel along with the main board.

10. Put the rest of the chassis with the screen and controls aside. Carefully place the back panel and main board on your workbench and loosen the three screws holding the bar that presses the two final transistors and the LM338 regulator on to the back panel heatsink. Remove the bar and three screws. The main board should be loose from the back panel now.

11. Unsolder the LM338. With the front of the main board facing you, it’s the first three pin device from the left on the back on the back that was against the heatsink.

12. Remove the main board screw at H1 and solder the black (ground) wire of the new switching regulator to the ground trace at H1, and replace the screw.

13. Solder the red switching regulator wire (+13.8 volt input) to the right-most pin where the LM338 used to be. This is the input pin shown in the diagram below.

14. Solder the white switch regulator wire (output) to the middle pin, where the LM338 used to be. This is the output pin shown below. (The first pin of the LM338, labeled “Adjust” below, will remain open.

15. Place the main board against the back panel. Place the bar that presses the final transistors to the heatsink place. Place the three screws back in, but do not tighten all the way. Leave them rather loose.

16. Place the main board and back panel together back into the main chassis. Line up the three front jacks (mic, earphone, cw key) to the holes in the front panel. Carefully push the back panel into place until it mates correctly with the side and bottom panels.

17. Line up the main board with the four screw holes. Place the four screws in, starting them, but leaving them slightly loose. After all four are started, tighten all four.

18. Tighten the three screws that are in the bar that presses the two final transistors on to the back panel heatsink. Use your best judgement. (I tightened until the two final transistors would not move with me pressing my finger nail on the side of them.)

19. (Optional step) Connect the power. Turn on the unit and use a voltmeter to verify that the white lead from the new switching regulator has about 5.4 volts on it. If it is not close to 5.4 volts, stop and troubleshoot. If it’s good, turn off the unit, disconnector the power, and proceed.

20. Re-assemble the remaining parts of the unit. Slide the pi and digital board subassembly back in, being sure to have the pins on the bottom meting correctly with the connector on the main board. Be sure to connect the gray ribbon cable to the back of the digital board (it is keyed so it can be inserted only one way), the white ribbon cable to the display unit (blue side down, silver side out), and black & brown power cable for the display going to the digital board (brown is down, black is up). The assembly manual has pictures that can help (https://www.hfsignals.com/index.php/sbitx-assembly-manual-v1-0/).

21. Reinstall the top panel, connecting the speaker to the digital board prior to putting the top panel on.

22. Connect the power, and power up!

This is how the installed regulator looks (installed on the PCB). It has been photographed outside the box for better clarity.

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The sBitx is a 25 watts, high performance SDR that you can easily build, it has all popular digital modes like FT8 integrated. This is a blog that gathers all the help, tips, modifications and information about this little radio.

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