uBITX Transceiver semi-kit build

Discussion in 'Homebrew and Kit Projects' started by KD8UYQ, Aug 14, 2018.

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  1. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Me again,

    Another thing that attracted me to the uBITX platform was the modification that replaces the standard 16 character 2 line display with a very cool color touch screen.

    2.8 display.JPG
    It took a couple of hours to get the Master Oscillator and BFO calibration values from the previous 20x4 display over to this 2.8" touch screen. Then when I finally did, it took another hour to tailor the S-Meter sample points in uBITX Memory Manager so that the S-Meter more or less matched what I was seeing on my the Icom IC-7300 via an A verses B comparison.

    color touch screen S Meter.JPG

    I have a bigger 3.5" touch screen that will be used in my final product radio.

    Lastly a 140 watt Solid State PA amplifier board kit with LPF filters for 80-10 meters was ordered from Communications Concepts Inc. this afternoon. It should be here in a week or so.


    KK5R, KE5OFJ, N1OOQ and 1 other person like this.
  2. W0VRA

    W0VRA Ham Member QRZ Page

    That's one outstanding write up. Well done, @KD8UYQ!

    For frequency calibration I used CEC's built in WSPR beacon functionality, and downloaded the reports from the WSPR website into a spreadsheet. The reports include the frequency they thought I was transmitting at, so I averaged that, and did the correction per Ian's example.

    WSJT-X has some sort of frequency calibration routine that will tell you the offset, but I haven't used it.
  3. K5MIL

    K5MIL Ham Member QRZ Page

    Here is my emergency power supply. I put a jack on my DeWalt 12 vdc cordless drill charger and by dropping the battery in the charger I can power the transceiver for several hours.

    Bill - K5MIL

    Attached Files:

    N7UJU likes this.
  4. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello Avro,

    Using WSPR is a good idea. I had the displayed frequency on the uBITx using the Raduino module matched with the 4 line blue display within 20Hz of the received frequency. I was happy with that.
    Instead of loading the uBITX firmware to support the Nextion 2.8" touchscreen on to that Radiuno I decided to take a new Ardunio Nano, solder on headers, and upload the UBITX_CEC_V1.095_NX.hex file to that. It worked fine except the displayed and receive frequency was off by 1100Hz as it was back on post #5 with the blue LCD.

    uBITX Memory Manager allows you to save a configuration to a file. I did that for the calibrated 20x04 blue display Radunio. My intent was to copy that config file over to the Radunio with the color touch screen. I'm sure that it being later in the evening after a long day had something to with my troubles but it took at least four tries and 2 hours of messing around before the calibrations took.

    ObviouslyI was doing something wrong. What does work is to connect up the mini USB cable to the Radunio, start the uBITX Memory Manager application, and click on the CONNECT button after selecting the correct COM port for your PC to Radunio connection. Next click on the "Load from File" button, select the file that you want to upload (in my case it was 20x4 config.btx), press the <=Encode button, then "Write to uBITX" button. That works.

    Hi Bill,
    Clever! I also like that you styled your project case to look like a Collins rig and labeled your uBITX as a KWM-2.5. I fancy myself as a Collins fan as well.

    The final uBITX build will have the capability to run on a built in 4S LiPo battery. There is a very inexpensive buck/boost module available on eBay that can regulate the 14.8 volts from the battery down to 12 volts at 5 amps. I have used them before for other projects and they work surprisingly well.


    W0VRA likes this.
  5. W0VRA

    W0VRA Ham Member QRZ Page

    There are a few µB users who have pushed the supply voltage to 15V, and a few others horrified by the idea.
    KD8UYQ likes this.
  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    I am leaning towards the scared guys. :eek:

    KK5R likes this.
  7. W0VRA

    W0VRA Ham Member QRZ Page

    If you're gonna put the buck circuit in anyway, you can run the 14.8 to the PA supply, and the 12V to the rest of the rig.
    KK5R likes this.
  8. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hi Avro,

    My next modification will be to even out the transmit power across the bands. We will see how that goes before I start making changes to the supply voltage. Besides my plan is to make a docking QRP radio. Undocked, the uBITX will transmit at whatever power it will put out. Docked, the uBITX transceiver will connect up to a 140 watt SS linear amplifier with a heftier power supply. The uBITX will select the proper LPF for the linear based on which band it’s on. At least that’s what I’m thinking about.

    W0VRA likes this.
  9. N7EKU

    N7EKU Ham Member QRZ Page


    Before doing that, you really need to head over to the bitx groups.io site and review the numerous issues with this transceiver. Many things need fixing before considering adding an amplifier to this rig.

    Spurs, harmonics, and IMD problems all need fixing, especially on the upper bands, and especially on SSB when adding a mic amp (as you've already done).


    KK5R likes this.
  10. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello All,

    This evening Alice's (KB1GMX) modification to even out the output power across the bands was implemented on my uBITX prototyping fixture.

    Q90 and R81 were replaced but according to the schematic for version 4 of the main board that is in my kit the 470pf capacitor (C81) was already in place. So no need to change it out.

    Alices mod.JPG

    The 4 2N3904 drive transistors were pulled;

    Alices mod pic 1.JPG

    and replaced with metal can 2n2222A transistors.

    Alices mod pic 2.JPG

    If you look carefully you can see that R911, R96, R941, and R942 are two 22 ohm resistors, one stacked upon another for a parallel resistance of 11 ohms per Alice's advice.

    Now for the test results. Before this modification was done my maximum power out was 12 watts on 80 meters and there was a 60% drop in output power between the 80 and 10 meter bands. After KB1GMX's mod was done the maximum output power on 80 meters increased a little bit more than 16% to 14 watts but more importantly the power output differential between 80 and 10 meters decreased to 39%.

    80 meters =14 watts
    40 meters =12 watts
    20 meters =12.5 watts
    15 meters =9 watts
    10 meters =8.5 watts

    In my opinion this modification is worth the time and effort.

    Good Evening
    KK4CUL, KK5R and KG5RKP like this.

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