BITX40 PTT Enhancement for Digital or CW

MiscDotGeek Co-Sponsoring Builders Fest 2018

The MiscDotGeek uBITX FAQ


The uBITX is out and folks have a lot of questions about the kit. It’s my intention to answer as many of them as possible. Note: Questions about building the uBITX, what skills are needed, and suitability for beginners are all answered in the BITX40 FAQ.

Check our post “Low Budget Tools and Parts For The Budget Builder” for tips on supplies and getting parts to work with.

How much does the uBITX cost, and where can I order one?

Pretty Maids All In A Row at the uBITX factory

Photo Credit: Ashhar Farhan

The uBITX went on sale on 12/9/2017 for $109. After the holidays it’ll be $129.You can purchase the uBITX at the official site,

Farhan’s goal has been to make high quality equipment available at a low price, as evidenced by the BITX40 only costing $59. The uBITX is equally affordable, while costing more than the BITX40 due to its higher parts count and more extensive labor required to build and tune the board.

How do you pronounce “uBITX”?

From the words of Ashhar Farhan, the creator of the uBITX himself: “I pronounce it as ‘micro bitx’, you can choose your own.” We all type “uBITX” but it’s not a “U” it is the symbol for “micro” which is µ, so it is technically the µBITX. Nobody has that key on their keyboard, however, and it’s not straightforward to type. This leads us to using “uBITX” and the pronunciation that often follows, “you bit ex”. As long as someone else knows what you’re talking about, any pronunciation will work 😉 

How is the uBITX different from the BITX40?

The uBITX has a lot in common with the BITX40. It is the next step in the evolution of the BITX40 design and has some significant technological differences, and many added features. Let’s look at a few of the differences between the BITX40 and the uBITX:


First and foremost, the uBITX is a multi band radio, and needs no modification to be active on all HF bands except 160m. That means you can use the uBITX on 80m, 60m, 40m, 30m, 20m, 17m, 15m, 12m, and 10m!


Another wonderful feature is that the radio has not just SSB, but also CW! One needs only to connect a keyer.

Raduino Differences

The Raduino is used but with a different program and slightly different hardware. The SIS5351 DDS chip has three outputs. The BITX40 uses only one output for the VFO. The uBITX makes use of all three. Instead of providing only the VFO it also provides the BFO. The Raduino is also responsible for providing the CW tone when the CW keyer is used.

The Raduino plugs directly into the uBITX board, rather than with wires to the main board such as in the BITX40. The uBITX and the Raduino can be separated, as long as coax cable is used to connect the signal wires to the main board.

Power Amplifier and Output

The inexpensive IRF510 is still used. Instead of a single IRF510, there are two of them configured in a “push-pull” configuration. This is done in order to produce a cleaner output, eliminating the need for a Low Pass Filter on every band. This is why you see 4 sets of filters, but 9 bands are supported. As a result there are two heat sinks.

The PA produces 10W on lower bands, but the output decreases on higher bands. The lowest output is 5W on 28mhz (10m).

How big is the uBITX?

The board itself is 6″x5.5″, with the heat sinks for the dual IRF510’s extending past the rear of the board. The Raduino protrudes half an inch from the front of the main board.

What are the extra resistors for?

The uBITX includes a 2.2k ohm and a 10k ohm resistor. They are for CW paddle. The 2.2k resistor goes between the CW input and the the Dot paddle, and the 10k between CW input and the Dash paddle.

Where can I get help with the uBITX?

Support for the uBITX is almost entirely community based. There are two popular communities. The first is the BITX20 mailing group, which can be used fully via the web, at The link is here:

Second is the BITX40 and uBITX QRP Radio Kit group on Facebook, with a link here:

Support for product shipping, pricing and other things specific to the purchase of the kit itself, please contact directly.

Further uBITX reading and more information

I’ve skimmed over the current information available, but there is a multitude of information in the technical discussions and circuit descriptions in the links below.

Farhan’s uBITX page:

Project announcement on the BITX20 group 3/2/17:

Problems with filtering 4/7/17:

Teaser about uBITX availability 12/4/17:


1 ping

Skip to comment form

    • Brian Ard on December 5, 2017 at 7:43 AM
    • Reply

    Can i get one built ? as i cannot build it ..
    Regards , Brian K4ARD

    1. The board itself is built, one has to put it in an enclosure of any sort, and do some basic soldering. Check the BITX40 FAQ (linked toward the beginning of this one) for details.

    • Brian Ard on December 5, 2017 at 7:44 AM
    • Reply

    opps K4ARD is my call sorry

    • K1RCE on December 6, 2017 at 12:06 PM
    • Reply

    As always Sir, an excellent article. Thank you for the included links. 73, K1RCE

    • Arthur Bryant on December 9, 2017 at 8:00 AM
    • Reply

    Do you think that a QRP Labs VFO would work on a uBITX?

    1. Hi Arthur, No I don’t think it would be a good fit. It could be made to work, I’m certain, but I don’t think it would keep the radio fully featured as designed. The uBITX Raduino is very specific to the uBITX, but the QRP Labs VFO is just a VFO, with no BFO or CW tone output.

  1. […] uBITX is now out, QRP Labs QCX is on the market, and the BITX40 is still a fantastic kit- Hams all around […]

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.