Tuesday, May 2, 2017

BITX40v3 Mod - C91 & C92

When the BITX40v3 is using the Raduino, the two capacitors C91 and C92 should be removed from the circuit board. These capacitors attenuate the signal coming from the Raduino which is not as big a problem on LSB (injected RF around 5 MHz or less), but is more of a problem on USB (injected RF around 19 MHz). In the newer Raduino sketches (such as v1.0.9 or higher) the drive level for LSB and USB can be set in the software.

The above picture shows an older BITX40v3 board where L4 had to be removed; on the newer boards, both L4 and the variable cap above it are not installed.
The wires from the Raduino to the connector shown above, should be kept as short as possible and routed in an arc up away from the circuit board. Even better is to replace the two wires with mini coax such as RG174. This will minimize the Raduino signal that could enter the circuit and cause other problems such as the harmonic mixing that causes a "birdie" on 7199 KHz.
I can still hear the birdie on 7199 on my BITX40, but it is quite low and doesn't interfere with signals on or near that frequency.  73,  AL - VE3RRD


  1. I know this is over 2 yrs old, but I just recently won an auction on an early Bitx40 V3 and it is partially assembled with an enclosure. I notice their was no raduino or display in the pictures of the Bitx40 and the parts that still needed to be installed. I have been looking for information about adding the raduino and if it was possible, what would need to be done and where I could find a raduino. Thankfully I found this site as well as a couple others, but I still don't know where to get the raduino. I have a display from my uBitx that I built, I replaced the original display with a Nextion display on the uBitx. Any help would be appreciated. I am a novice when it comes to building, but I am an Extra class amateur, been in ham radio since 1996. Again thanks for sharing all this information on the Bitx40!! 73 WD8WV

  2. A couple of us in the group purchased the original BITX40 without the raduino. It was very unstable and shifted frequency as you transmitted! The raduino was offered by hfsignals.com as an upgrade so we immediately purchased it.
    When converting the Bitx40 to use the raduino, you must disable the on-board VFO circuit by removing the toroid L4, and the two capacitors C91 & C92.
    Info on wiring the Bitx40 can be found on the http://www.hfsignals.com/ website and support is on https://groups.io/g/BITX20 . You can check with hfsignals@gmail.com to see if the Bitx40 raduino is still available for purchase, and also ask if anyone has one for sale on the groups.io site (and also on the Facebook Bitx groups).
    73 .. AL VE3RRD