Belt and braces filtering of a BITX40 power supply

Akira JJ1EPE had spuries on his BITX40 at 75kHz.

The modification for suppress the spurious signals provided by a friend involved the following steps:

1) Add 3.3uF electrolytic capacitor to VCC line of Arduino board


2) Add 0.1uF x 2 bypass capacitors to the VCC line (fuse point)

3) Insert high frequency choke of about 100 uH in the power line of Arduino

4) Connect the minus line of power supply line to the ground

5) Connect the minus line of BITX40 main board to the chassis ground

6) Add 0.1 uF × 2 bypass capacitor to VDD of BITX 40 board

7) To prevent common mode noise, add 0.01uF x 2 bypass capacitor to the power connector

This series of steps could equally well be applied to the µBITx if you have noise from your power supply and want to get rid of it with a very thorough strategy.


An amazingly smart idea for extra I/O ports

Tom WB6B want to expand the number of digital and analog I/O pins available to him in adding enhancements to his uBITx.

He came up with an ingenious idea, by creating a Smart LCD Backpack to replace the commonly found ones on inexpensive 2×16 and 4×20 I2C displays found on eBay and Amazon.

He has uploaded a library to GitHub that allows you to program a Arduino Nano to emulate the common I2C to parallel backpack used on an I2C display (either size). The Smart I2C Backpack, additionally, allows you to read and write the analog and digital pins on the Smart I2C Display Backpack.

The package includes a interface library that you include in your code to interface with the Extended I/O functionally. Also included are two example sketches. One is the code you program into the smart backpack. The other is a demo/test program you program into another arduino and connected via the I2C bus to the Smart Backpack Display.

The Smart Display Backpack should work with firmware using standard I2C LiquidCrystal drivers such as the KD8CEC firmware.

The code uses libraries that are installable from the Arduino library manager,.  The GitHub URLs are just for reference.

The following libraries should be part of the base Arduino software install:

  • Wire
  • LiquidCrystal

Tom hopes that others will enjoy this new display and I/O expander.

And the link to the code …


Adding the v4 pop fix directly to a v3 board

Nigel G4ZAL has added the v4 pop-fix to his v3 board by placing components directly onto the v3 board.


  1. Swap out R70 from 100 ohms to 1K.

  1. Drill a small hole (0.7mm or similar) to the right of R70 so as to be able to fix the 2N7000 transistor.
  2. Pin 2 of the 2N7000 is soldered on the underside of the board (ground).
  3. Scrape a little varnish from the tracks and tin ready to fix the 2N7000.
  4. Add some Kapton tape to stop any shorting of components.
  5. Add the remainder of the components and run a bit of enamelled wire to the trace near the Raduino headers to pickup the T/R line.

Seen from the front of the main board (ignore the cutouts on the front of the board)


LED power out indicator

Lee  “I Void Warranties” N9LO ran across this circuit when looking for a transmit indicator for his Small Wonder Lab PSK31.

[Note the circuit was originally drawn incorrectly, but has now been updated]

Lee threw it together (there are not many parts) and it lights up bright and solid for CW and you an watch your modulation on SSB.   I can really see the difference when I switch in my SSM2167 module.

Jerry KE7ER recommends placing the circuit before the transmit LPF, not at the antenna port.   The diodes potentially create a bit of harmonic content that the LPF’s would remove.


KD8CEC firmware hint – CW frequency display

The KD8CEC firmware provides a lot of customisation features through uBITx Manager software.  Many user of Ian’s firmware are not aware of all the built-in features of his firmware.   This is one such instance!

JJ1EPE raised a concern that his display in CW mode was “off frequency”.  Well, it was from his perspective, but then the display was all the time showing the TX frequency not the offset frequency where the station he was listening to.

CW offsets create headaches in how you represent the frequency on a display.  In SSB the frequency you see on the display is the frequency of the suppressed carrier on receive and the same on transmit.   If you tune to the carrier frequency of a received station you won’t hear anything.  To get a sidetone we have to tune off the transmit frequency by a few hundred hertz.  Most people have worked out how to set the offset on the uBITx.

The standard that Ian KD8CEC has applied is to always show the TX frequency  by default (except where RIT or SPLIT mode is selected).

However, if you want to change the approach, do the following in uBITX Manager:

– Enable Adjust CW Frequency

– Shift Display Frequency on CWL, CWU Mode

If you select this function, the LCD will show the frequency at which the radio is being transmitted (the offset you prefer is added or subtracted to the actual RX frequency reflecting the CW-L or CW-U mode selected).   This may be just the thing you were looking for!