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

    Hello Floyd,

    No sir, not really. If you are comfortable downloading applications to a PC then running them you will be fine. The software that comes loaded on the uBITX supplied Raduino module works fine but is lacking in some functionality that folks are use to on 70s or 80s vintage radios on up.

    I would recommend going to Ian's web site and down loading the .Hex files applicable to the display that you are using. Then use XLoader to load the firmware on to the Ardunio Nano There is much more functionality on Ian's version of software then what comes with the stock uBITX kit.


    The easiest to use firmware loader for a Ardunio based processor is XLoader.


    Ian also provides a step by step guide on downloading XLoader, configuring it and using XLoader to upload firmware to a Arduino Nano micro controller.


    The actual process to upgrade the firmware itself takes about 20 seconds and it is well worth the effort.

    BTW the display that comes with the kit is a 16 character by 2 line parallel display. Ian's 1.095 version of firmware for it is UBITX_CEC_V1.095_16P.hex. The 20 character by 4 line parallel display that I am using on my prototype and test setup uses the UBITX_CEC_V1.095_20P.hex firmware and so on.

    There is firmware for the really cool color touch screen Nextion displays, dual displays, and ever serial communication displays.

    This really is a dandy platform for the experimenter.

    KK5R likes this.
  2. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello All,

    I started wiring up Kee's AGC board, The receive line between K1 and K3 on the uBITX main board was cut so that a header could be placed in line and provide an input and output tap for the AGC circuit.

    Receive line header.JPG

    Receive line header2.JPG

    I coax cable runs between the uBITX main board, AGC board, and RF gain pot have been completed.

    coax cables to AGC board.JPG

    Next up are the connections to the AF pot, 5 volt power supply, and AGC switch.

    KK4CUL likes this.
  3. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Oh By The Way,
    Today while I was working at the Radio Museum I came across this 70s vintage Robyn CB radio in one our storage building.

    Robyn GT-401D.JPG

    Notice that the CB radio itself can be removed from the clock radio/power supply cabinet and mounted in the car or used where portable operation is desired.

    Robyn GT-401D pic2.JPG

    I brought it home this afternoon to see if it could be reworked for my uBITX project where both base station and portable operation are desired. If I was using the 16x2 display instead of the 3.5" color touch screen maybe, but after further consideration I think not. However, I did get several ideas as to how to design my own docking station.

    Robyn GT-401D pic3.JPG

    Robyn GT-401D pic4.JPG

    KK4CUL likes this.
  4. N1OOQ

    N1OOQ Ham Member QRZ Page

    Gotta love the 70s... Mechanical clock, LED channel number on the CB, lotsa chrome.
  5. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Yes sir, It does have that 70s styling of a lot of the cheaper made consumer grade technology of the time. Several makes and Model of 8 track players come to mind.


    As a side note, we get dozens of CB radios donated (dumped) at our museum annually. The significant or unusually ones are put on display. The rest are sold at any of the three auctions that we hold each year.

  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello all,

    The ND6T/K5BCQ AGC mod works very well! I highly recommend that some kind of AGC circuit be added to the uBITX transceiver and the one that these two folks developed is really good. I notice just the slightest thump on the first syllable of the first word when a very strong signal is attenuated. Nothing objectionable plus it doesn't keep occurring on every phrase.

    Boy what a positive improvement it makes in the enjoyment of using this little QRP rig.

    AGC mod.JPG

    The small black knob is mounted on a 500 ohm potentiometer (chosen because I had one) which manually controls the RF gain. It works fine but on the other uBITX rig that I will be building a 1K or 2.5K pot will be tried.

    Keeping with the design criteria for this prototyping setup in which the uBITX main board and the Raduino module could be changed out in less than 2 minutes I decided to add a separate 5 volt regulator to power the AGC circuit. Taping the 5 volt regulator on the Raduino module would have complicated the exchange for a different one.

    One thing that I like about about Donald Cantrell's circuit design is the ability to select the AGC hold time. Based on his recommendation a three position toggle switch was installed with LEDs. This allows me to select either a Medium or a Long hold time constant or turn off the AGC circuit altogether.

    AGC switch.JPG

    In the picture the AGC switch is in the Medium position, center position is Long.

    AGC switch off.JPG

    The orange LED is illuminated meaning that AGC is off.

    This AGC circuit has a bonus. Taping across c4 (1 uf capacitor) provides a signal to drive a S-meter. That is where I am headed next.

    Last edited: Aug 26, 2018
    KK5R likes this.
  7. K5MIL

    K5MIL Ham Member QRZ Page

    I added a mic preamp to my uBitx with a mic gain control on the front panel. I used the mic element that came with the kit and mounted in a small aluminum flashlight case. The mic element is held in place with silicon glue. The preamp is powered by a 5 volt regulator that is mounted on the rear panel. I made my first SSB contact the other day on 40 meters with a station in Louisiana and got a good signal report.

    Bill - K5MIL

    Attached Files:

    W1TRY and N1OOQ like this.
  8. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello Bill,

    Clever use for that flashlight. A microphone amplifier is also on my mods list for the uBITx transceiver but first I have to figure how to implement a relativity accurate S-meter on the digital display. It is turning out to be more involved than anticipated.

    BTW you have a very nice ham shack.

    KK5R likes this.
  9. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello again,

    The uBITX now has a functioning S Meter.

    uBITX S Meter.JPG

    To even have the capability to show an S-Meter on the LCD display you have to be running KD8CDC, Ian's firmware rev 1.07 or later on you uBITX transceiver. As you can see on the picture above I have v1.095 loaded on my unit.


    The S Meter is not enabled as a default setting in any version of the firmware mentioned above. To do that you need to download a very cool application called "uBITX Memory Manager". Get version 1.081 here

    What uBITX Memory Manager is is a GUI to edit settings in KD8CDC's firmware without having to use Ardunio's IDE software development tool. This YouTube tutorial will give you the basics as to how uBITX Mem Manager works.

    In brief, after downloading uBITX Manager and extracting the files I copied and paste the uBITX Memory Manager.exe application to my desktop and double clicked on it. Windows 10 will block it from running so when it does click on the options box and click on "Run Anyway." Click on the com port that matches the setting of the mini USB cable that is connected to the Raduino on your uBITX transceiver (com 3 on my computer).
    Click on CONNECT, in a few seconds the READ uBITX box with turn a pale blue. Click on it, then click on the Decode -> button.

    Scroll down until you see this.

    uBITX Manager s meter.jpg

    Put a check mark in the S Meter box then click on the S Meter Assistant box and follow the directions in this link

    It is a clever tool and when I was done my S-Meter sensitivity cure looked like this.

    uBITX Manager S Meter assistant.jpg
    The slider controls let you tailor the sensitivity of each S unit threshold with the end result shown on the LCD display of my little uBITX rig at the top of the this post.

    But I have to back up a bit. There is not enough signal from the AGC board to drive the A7 line (Purple wire from the Raduino digital connector) and get any indication on the 5 Meter display. KD8CDC shows a couple of ways to make a S-Meter sensor/amplifier. I made mine from a LM358 because I had several on hand. The gain on his sensor is 10X. I needed 100X to get enough output signal for the Raduino to detect reliably.

    S Meter sensor.JPG

    I made the capacitor (orange component in the picture) easy to change to adjust the hold time constant for the S Meter graphic. The link to roll your own S Meter sensor.


    In the end I decided not to use the AGC board as my tap point for the S Meter sensor. The capacitor that sets the "C" for the AGC time constant held the S Meter graphic to long on the display. Instead I choose the high side of the volume control.

    S Meter sensor 2.JPG

    The S meter display updates more to my liking with the tap point for the sensor coming from the fixed side of the volume control. I still have some tweaking to do to capture a 40uV S9 more accurately but I like what I have so far.

    KK5R likes this.
  10. KD8UYQ

    KD8UYQ Ham Member QRZ Page


    Yesterday afternoon I dragged out the HP 8657A Signal Generator, set it to 14.200Mhz and 40uV then injected the signal into the antenna connector of the uBITX transceiver. The tuning knob was adjusted for maximum bars on the display. I was getting five bars but wanted the sixth bars to represent S-9 so I pulled up the uBITX Memory Manager program, went to S Meter Assistant and adjust the sliders down a bit.

    uBITX Manager adjusted for S9.jpg

    Back over to the test bench to check the results.

    HP Gen S9 check.JPG

    S9 bars.JPG

    Close enough. Injecting 40.3uV is just enough to flip the 6th bar on. about 58uV turns on the first plus sign (10 over S9) and I forgot what it took to light the second plus sign for 20 over but as far as I am concerned it is as accurate as I want to mess with it.

    On to the next modification.

    KK5R and N1OOQ like this.

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