uBITX QRP Transceiver

Last year I assembled a BITX40 QRP transceiver from a kit and it turned out well. For under $60 it is a surprisingly good 40 meter radio. Now it has a big brother that adds more bands, more power, better performance, more features, and is still incredibly affordable. It’s also easier to build.

The uBITX is much more than just a multi-band BITX40 (the uBITX covers 80-10 meters); the receiver is much more refined and the difference between the two is not subtle at all. The uBITX has much cleaner audio and sounds more like a commercially available radio than the BITX40. It also tunes like one with a proper encoder for tuning instead of a potentiometer. To access the various modes and features of the radio there is a clever menu system that makes use of the encoder’s built-in pushbutton for navigation. Like the BITX40 before it, more advanced firmware (firmware upgrade instructions) has been developed for the radio’s microcontroller and a ton of features have already been added (Rig Control, IF Shift, CW keyer, memories, band limits, WSPR, and many more).

The amount of improvements implemented in the uBITX are especially evident in the assembly process. Where the BITX40 had many individual connections between components and the pre-assembled boards, the uBITX needs only four:  power, antenna, audio, and digital. This makes wiring the uBITX a much simpler process than its predecessor. The one added complexity was aligning the screen with the cases front faceplate since the screen’s header now plugs directly into the main board instead of using a cable.

My uBITX build is similar to that of my BITX40. I used the same style case made of shielded ABS plastic with aluminum end plates (Hammond 1598RDBK) and a top mounted speaker. Due to the additional band capabilities and other upgrades the main board is about a half inch bigger in each dimension. This small change required me to use a different case model from my previous build.

The case’s removable end plates and the socketed board connections make it very easy to assemble & disassemble the radio. I kept the wiring as short and tightly bundled as possible in addition to using small coax for the antenna connection to try to reduce interference. Beyond the standard controls and connections I added a power switch, used a USB panel mount extension to provide easy access for firmware updates & rig control, installed a pushbutton in place of a CW key jack to use as a tune button, and upgraded the volume pot & audio jacks to higher quality versions than those supplied. This also allowed me to use the volume and tuning knobs that I liked. The headphone jack is wired such that it cuts off the speaker when headphones are plugged in.

If you want to build a simple, but still perfectly usable radio the uBITX is absolutely the way to go. It offers many more features and vastly improved performance over the BITX40 for less than twice the price at $109.

Update – Two Simple Mods (January 2019)

Sources for tons of uBITX mods and upgrades

  • Audio Pop Fix – Solves the issue of getting a blast of audio static from the speaker when switching from receive to transmit. This fix has been incorporated into the new v4 circuit boards (v4 schematic), but since mine is an older v3 board (v3 schematic) I did the mod myself. I followed the guides here, and here and mounted the parts directly to the board similar to the latter example. What I like about this method is that everything fits on the main board so final result is fairly clean. This mod involved drilling a hole in the board and scraping off some of the insulating film on the bottom, as well as exposing a few traces on the top side of the board. The mod works perfectly and looks more tricky than it is if you take your time. Be careful to get the orientation of the transistor correct since different parts have different pin-outs.
  • Increase Mic Gain – The default microphone gain is inadequate for the three different mics that I have tried. I could never drive the transmitter properly with a normal speaking voice. This super simple mod definitely improves the microphone response and is highly recommended if you have poor microphone response, even on the new v4 boards which do not incorporate this mod. There are more complex microphone mods around but this one works well and only involves replacing two resistors.

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