Monday, April 24, 2017

New features for BITX40v3

The latest v1.07 Raduino software can be downloaded from , and the user instructions are found at  .
This new version adds upper sideband so that now the BITX40 can be used for digital modes on 40m. Note that you must use the si5351 v2.0.1 library with the Arduino IDE for it to compile. You must also add a "Function" pushbutton to access all of the new features, which are listed as:

Added functionality via the Function Button
  • Use a pushbutton to momentarily ground pin A3 (orange wire). Do NOT install an external pull-up resistor!
  • dual VFO A/B capability (RIT is not yet working though)
  • LSB/USB mode selection
  • Settings menu for calibration, tuning range, VFO drive level
  • All settings are stored in EEPROM and read during startup
Here is a picture of my BITX40 receiving JT65 on 7076 KHz. The USB bandwidth is a little narrow to receive the entire JT65 band, but by tuning up 1 or 2 KHz, it can be covered. I haven't gotten the transmit working yet.  73, AL - VE3RRD

Here is a picture of the BITX40 receiving WSPR on 7038.6 KHz USB. I am using the software WSJT-X for both modes.

Sunday, April 16, 2017

Minimum BITX40v3 Hacks

The two mods that everyone should be adding as soon as they get their BITX40v3 are the Q13 protection diodes at K1 and the 2nd harmonic reduction mod (100 pF NPo 100V capacitor across L7 in the output filter). 

The Q13 protection mod is extremely important as there have been hams who have blown Q13 within hours (or even minutes) of getting their new BITX40v3 working and hooked up to an antenna. The cause is because they transmitted on a nearby antenna with their 100W or higher station rig while the BITX40 was receiving on its antenna.

The symptom of a damaged Q13 is that receive still works fine but there is no transmit. Note that although Q13 is a driver for the transmitter circuit, its base is connected to the antenna during receive.

Q13 can be replaced by a 2N3904 transistor (there is an SMD version if desired). 73, AL VE3RRD

The 2nd harmonic is a little too high for North American standards. Add a 100 pF 100V NP0 capacitor across L7 in the output filter. This will reduce the 2nd harmonic by about 20 dB. If you are planning on increasing the output power above the normal 5 to 7W, then you should use a 200V capacitor.