Variable power supply

One of the discussions on the BITX20 IO list over recent weeks has been a variable power supply to control power out on different bands.   This seemed like the wrong approach to addressing variable output of the µBITx to the editor of (where the problem of inadequate drive or inadequacies in the PA design should be addressed directly) until he spotted this circuit diagram drawn up by Walter W9KJO, based on earlier suggestions.     It is simple and straight forward with the TIP142 device at the centre of the “buck” function.   24v input can be adjusted downwards to set the power output of the µBITx PA stage.

Walter says, “It controls voltage nicely. Really helps limit output power while working digital.”

However the TIP 142 really generates some heat.  He has a heat sink on the device, but the heat sink will need to be much larger to be safe.


A cheap logic analyzer to inspect uBITx CAT operation

Rod KM6SN notes that  KD8CEC software will run in a stand-alone separate Arduino Nano which is not connected to a uBITX.  This means you can look at the CAT serial link operations on your computer.

Rod mounted a spare Nano on perfboard so he could access the UART RX and TX lines and the Nano Reset line, and installed the KD8CEC software on the Arduino Nano.   The test jig and  ESD ground plate underneath are shown in the photo above.

Some time ago Rod  purchased a Saleae 8ch logic analyzer when they were still cheap. I used it, and enjoyed it for about a year.  Then, an ESD accident blew the Saleae. I looked online and did not like the new Saleae prices, so I purchased a cheap Saleae clone (USBee AX Pro) for about $12. See:

Unfortunately, the folks at Saleae got upset at all the clones, and changed their software so that it would not work with the clones.

So, I went to the USBee web site to get software, only to find out they wanted $20 for it. Being a true blue amateur op, Rod did not want to pay $20 for  proprietary software linked to one piece of hardware only.

After some digging he uncovered what appears to be an excellent open source (i.e. FREE!) logic analyzer called  PULSEVIEW/sigrok.


PULSEVIEW provides for decoding protocols, such as I2C, UART, CAN, 1wire, and many more.  Sigrok is the command line version, and PULSEVIEW is the GUI on top of the command line that provides a graphical display of decoded serial link.   PULSEVIEW/sigrok supports an impressive list of hardware analyzers. Furthermore, PULSEVIEW/Sigrok supports data collection from some digital multi-meters, and digital oscilloscope dongles.  For more information see:

Apparently some logic analyzers have an analog channel, and PULSEVIEW can show the analog signal as you would see it on an oscilloscope.

Here is an example PULSEVIEW screen showing a UART serial link decoded.
Channel D0 is Nano UART RX, channel D1 is Nano UART TX, channel D2 is Nano reset line:

Not bad for a $12 investment!!

PULSEVIEW/sigrok installation instructions

For Windows:


For Linux:

After installing Pulseview, install the firmware for the USBee AX using these instructions:

In Linux, use sudo to copy the attached file 99SaleaeLogic.rules into /etc/udev/rules.d

Remember to add your username to the plugdev and dialout groups.

Missing components on uBITx board

Don’t worry about the two missing components on your µBITx board.

C210 and C216 are shown as of 0pF meaning they are meant to be not fitted on the board.  The 45MHz filter was originally just an LC circuit, but in the production version a 45MHz crystal filter was incorporated into the design.

Audio Pop mod from QCX submitted by Greg N3NW

This audio pop mod from Greg N3NW appeared on the BITX20 lO Group list before this website went live in January.   The implementation may not look that elegant (sorry Greg), but this was about an experiment to reduce pops not an entry in a beauty contest!

Greg “borrowed” a rather elegant circuit snippet from the QCX transceiver that takes care of the pop completely.  This is effectively the same mod as that submitted byJoe VE1BWV (and no doubt taken from the same source) who confirmed that it works.  The mod has now been confirmed independently by both Pete W8KS  and John AD0RW.    So this mod, is known to work, however, it may come with one downside, for which John AD0RW has a work around.

The circuit diagram for the popular QCX transceiver (developed by QRP Labs) can be found near the end of the very well documented assembly guide for this single-band CW rig.  An excerpt that contains the TX Mute circuit installed by Greg can be seen below:

The TX mute switch in the QCX involves just 4 parts – a BS170 (Q7 above), a 0.1µF capacitor (C52 above), a 1N4148 diode (D5 above), and a 120K resistor (R60 above).

Greg used a 300K resistor for R60,  and a 440nf capacitor for C52 to adjust the timing, which keeps BS170 open just long enough when switched back to RX to remove the pop.  The CW sidetone gets weaker with this, however in my uBITX board 10K R253 was replaced by a 1K resistor to make the CW tone just loud enough with this mod.

Pete W8KS has, however, found that the CW sidetone (even after replacement of R253 with a 1K resistor) to be insufficient and asked for suggestions to address this mod’s shortcoming.

John AD0RW found a much better place to connect the drain of the MOSFET. First he replaced R70 (in µBITx circuit diagram (see circuit excerpt above) with a 510 ohm resistor.  Then he connected the MOSFET drain to the relay side of that resistor, i.e. to the point M2 on the schematic above.

This setup still shorts the incoming audio to ground and kills the pops, but leaves a voltage divider of R253 and R70 connecting the sidetone to the volume control, increasing the amount of signal injected.  Depending on your value of R253, this may be perfect as is. The value of R253 varies (some early production kits had a 1K resistor and more recent kits get a 220K resistor).  John’s was 220 k and he needed more volume, so he put a 50 k trimpot across R253. It is just about right at maximum resistance, but can be adjusted downwards if more volume is required.  If your R253 is a smaller value and the sidetone is too loud, just replace it with something of higher resistance.  The volume control now has final control over the sidetone level and can be tweaked in operation if needed.

Reference 1
Reference 2

Mic Compression and Noise gate with SSM2167 module

John, VK2ETA, has  used the small circuit board “SSM2167 Microphone Preamplifier Board Preamp COMP Compression Module DC 3V-5V”available on eBay or Aliexpress as a compression and mic pre-amplifier.

He simply connected the input to the mic, added a 4.7K ohm resistor between the mic input and the 5VDC (taken from the Raduino) for biasing the electret and put a 10K ohms potentiometer in the output to adjust the power level to the mic preamp stage.

He didn’t modify his uBitx board,  but simply inserted the board prior to the mic input.  The gain of 20dB is reduced back with the output potentiometer. John removed the “R1” resistor and replaced it with a 51K Ohms resistor to get a 4:1 compression factor, up from the 2:1 as delivered, but this change has yet to be tested “on air”.

John hasn’t received any negative feedback about the compressor except when I pushed the output potentiometer too high.



Simon VK3ELH used the same board and a similar scheme for powering the module from the regulated 5v line on the Raduino.  It is also installed separate to the main board and inline with the mic input.

Simon used a 75k ohm resistor for compression and 1k ohm resistor for the noise gate and a 100k pot on output. At full output, his audio was readable but distorted based on an audio check QSO, so the output has been turned down.

He put a larger heatsink on the IRF510 to cater for the higher average output, as the stock one was getting warm!

A side effect of the mic being on all the time is that there is leakage through to the speaker and it causes some feedback if the mic is within 2 inches or so of the speaker.

uBITx gets WSPR in Firmware

Ian Lee, KD8CEC,  has released a new (Beta) version of his µBITX Firmware CEC Version 1.04.   This version adds the WSPR TX mode.  It still needs wider testing before a release version is posted.  Ian is looking for beta testers who have a µBITX, can install his firmware and his PC Software – uBITx Manager that allows for easy configuration of firmware settings, and know how to use WSPR.

The WSPR function has been squeezed into the small programming space of the µBITX (32Mb) including the station callsign, location(2alpha, 2 number), dB and frequency information to be used for transmission.

As a field portable unit, you only need to bring the µBITX and antenna  to transmit WSPR as all information is already contained in the rig (no computer is required).  You do not need to make any modifications to your uBITX to use WSPR.

For more information, visit Ian’s website at:

KB1OIQ Mods to BITX40 and uBITx – particularly for Blind Ops

Andy, KB1OIQ,  has uploaded his Arduino sketch files, photos, videos, and documents describing modifications he has made to his BITX40 and uBITX QRP transceivers to Sourceforge:

Andy has done extensive modifications to his hardware and software, so don’t blindly download these sketches and expect them to work!

It is his hope that constructors will be inspired to make these modifications on their own transceivers. He has used a large percentage of VU2ESE’s original code, and added quite a bit of his own.

Andy says …

“I have had a GREAT deal of fun doing this work, and I want to share it.”

Notable features for each rig:


  • keypad
    • Explicit speaking of mode, VFO, and frequency by keypad button press
    • Numeric frequency entry via keypad
    • common radio functions via single key press
  • RF gain circuit
  • software voice synthesis with Talkie library
  • standard ICOM MIC connector using UP/DN buttons and audio out (for digital modes)
  • fine tuning potentiometer
  • added USB (for digital modes)
  • save/restore rig parameters to/from EEPROM
  • audio mixer circuit so synthesized voice and “radio sounds” can be heard in one speaker


  • text-to-speech voice synthesis via Emic2
  • keypad
    • Explicit speaking of mode, VFO, and frequency by keypad button press
    • Numeric frequency entry via keypad
    • menu navigation
  • wired CW jack for use with either paddle or straight key
  • paddle supports left or right handed operation
  • converted LCD to I2C (requires Adafruit LiquidCrystal and SoftwareSerial, frees up 6 Arduino digital pins)
  • refactored the code into C++ classes (all text strings in PROGMEM)
  • reimplemented the menu system with the MenuSystem class
  • removed (perhaps temporarily) CAT and factory alignment to make room for other features
  • disable transmit if outside of USA ham bands
  • CW mode with correct frequency display
  • VFOs are saved/restored in/from EEPROM (mode and frequency)
  • Text sent to the LCD is simultaneously spoken by Emic2
  • Extensive menu selections
  • Several visually impaired amateur radio operators are interested in this work!  I am excited by the possibilities.

Andy has a long list of things still TO DO on his uBITX.  His current plans include:

  • keypad
    • decide which features to add to individual keys
    • currently: frequency input, speak radio settings, menu mode
  • RF gain circuit
  • AGC circuit
  • anti-POP circuit for TX/RX transitions
  • fine tuning
  • test and perhaps tweak RIT
  • add MIC and signals for digital modes at the MIC connector
  • USA 60m channels to memory for easy user recall
  • TBD other features that might be useful to visually impaired operator
  • split mode
  • if memory allows, put CAT control and factory alignment routines back into the sketch

PC Switch Box Case

KP1JBW has a great memory.  He remembered a post for the BITx40 that covered using cheap surplus PC switch boxes for cases.

He says “this one was perfect and cost only $4 from an electronic surplus store. My radio literally just arrived this afternoon so I quickly ran out to find a case.”

KP1JBW will add a plate on the back to cover the cutouts for centronics connectors that came with the case.

The original center switch hole is where the display naturally sits when plugged directly into the board. I will end up popping the front plate onto the mill to get a clean and square hole. This case is steel so I might end up going for something down the road that’s lighter. For the price along with a massive selector switch, wire, and a decent set of knurled machine screws, I cannot complain. I bought a larger case for $6 when I need to start looking at upgrades.

Joe KD2NFC made a smart comment about the challenges of wiring up all those cables to the Arduino Nano – there simply won’t be enough ports!

John AD5YE commented that these boxes were either serial or parallel distribution switches.  They take a serial port computer output (6 to 20 wires), or a parallel port (usually 20 wires) and transfer this to 4 different receiving ports. The most common use was to connect one computer to several different printers. They were quite common in computers before the advent of USB and (lately) wifi.

He suggests finding one nowadays at a decent price is a rarity. A few years back, they were very common and very cheap.  However, they make excellent radio cases though one usually has to redo the front and back parts.  John has several with double-sided PCB added as faceplates. In addition to the cases, you usually ends up with a 12P4T switch (which is fine for switching filter banks), and lots of #28 wire.


RaduinoUmax shipping

Mike, WA6ISP, is shipping the first of his new Ubit RaduinoUMax Raduino replacements  today.

Mike says he has been working like a beaver since the PCBs arrived.

The MAX is for the 16 Added I/O pins on the end of the PCB.   It makes the PCB a little longer, but still fits into uBitx Radio PCB.   I2C control gives you 16 more 5V digital I/O ports and uses an Adafruit Library for simple control.   Three I2C address jumpers are provided so you can use other I2C modules.

Reference 1
Reference 2

VU2ZAP experiments with TDA2822 Audio Chip

Raj VU2ZAP has done some experimenting with TDA2822 chip failures.

FCI chips were sourced locally and plugged in. No failure was observed when using the chip with normal volume.  However, when he raised the volume to a high level the chip failed immediately!


1: Add a resistor in series with the 12V line maybe 10-15 ohms to drop the voltage.

2. Simple solution is to use only a 16 Ohm speaker or add a series 8-10 Ohm resistor with the 8 ohm speakers.

3. Cut the power track to the TDA and insert a 78L08 or 78L09 to reduce the voltage. There is a convenient track which can be cut.  Solder either an SMD or DIL regulator onto the board at this point. This track leads directly to the chip and filter cap (see photo below).

The center lead looks soldered, but is in fact floating.  However, the tab is soldered to the copper groundplane below. The white wire is part of Raj’s fix to prevent the filter relays from clicking during PTT.  Raj suggests the board as illustrated now needs a brush cleaning!

Raj observes that with this mod, audio is fine but distorts at high volume. The 9V voltage out does not drop at maximum volume.

Feedback on the solution from Jerry KE7ER

Jerry KE7ER says “This looks like a fine solution!   The fact that the 78L09 inherently limits current to something reasonable is a bonus.  And it fits in there perfectly!

Jerry suggest that it might be a little bit easier to just rip that trace out entirely. You could place the part up against the through-hole on one side and run a short wire to the other through-hole.

Gain should remain as it was at 12v.   Just that when you turn the volume up it distorts earlier.

If what you have on hand is the TO220 LM7809 (or any voltage from 5v to 9v), it will fit in there nicely as well.  Glue it face down to the board with pins hovering over  the trace that Raj has cut.   Or, if you don’t like glue, solder a short wire from tab to ground plane.

ST makes the 78L** parts in a SOT-89 package.   This is the same package as U2, the 78L05 for the IRF510 gate bias.

TI and Fairchild LM78L** parts only come in the SOIC-8 and TO-90 (also some dinky BGA that we don’t want to talk about).  Digikey and Mouser don’t sell ST’s SOT-89, so a bit harder to obtain. The SOIC-8 should do fine, solder the ground pins to the ground plane for heat transfer.   The TO92 could work, although it would likely heat up faster because the heat has nowhere to go.

The maximum available current draw from a 78L09 would limit the maximum audio level.    Apparently this provides enough audio for Raj, and limiting that current does protect the TDA2822.   If it gets to be too much current for the 78L09, it will shut down till it cools off.   Just what we want, if it’s enough audio power for your situation.

If you want more power and less protection, use the 1 Amp TO220 LM7809 (or 08 or 06 or 05) face down, flat on the board.   ST sells the 1 Amp L78** in the Dpak/TO252 package, about the same as the TO220.  TI sells the 500ma LM78M** in the Dpak/TO252 package, might be an ideal solution for moderate levels of current.

Any of the above could be made to work, and in fact any regulator providing between 5 and 9 volts.   This assumes you don’t have one of the clones made from factory floor sweepings that smokes at 7v.