uBITX Transceiver semi-kit build

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

ad: L-HROutlet
ad: l-rl
ad: Subscribe
ad: abrind-2
ad: Left-2
ad: Left-3
ad: QSOToday-1
ad: L-MFJ
  1. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Although there probably have been thousands of these 80-10 meter QRP kits sold worldwide I only became aware of their existence about a month ago when a fellow volunteer at the Radio Museum came in with one. At first I didn't pay much attention to him or it until he showed me this video review on YouTube.

    After watching the video and finding out how much can be done with this less than $150.00, shipped, kit I decided to order one (actually I now have two).

    I spent the extra $10.00 shipping from India via DHL and received my kits in about a week.

    Inside of the plastic box was the main board, "Raduino" daughter board and, a bag of parts. You only have to provide knobs, a 12 volt 5 amp power supply, a speaker, and some kind of case or cabinet. Like the video shows the kit comes with a microphone element and a PTT button to make your own hand mic.

    STH70552.JPG STH70553.JPG
    One thing that I neglected to mention was the amount of internet support there is for the uBITX transceiver kit. There all sorts of folks doing hardware mods and enhancements to the kit not to mention the individuals hacking (in a good way ) the firmware for the Raduino. For example I bought several different displays to play with including the Nextion 2.8" and 3.5" color touchscreens


    Here is the primary site that I consult for the uBITX but there are many more. https://ubitx.net/



    To be continued....
    K9CPO, KK5R, KC8YLT and 2 others like this.
  2. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    As I mentioned before I have two of these kits. One is mounted on metal plate and is my prototyping setup to test modes and upgrades without having to do this stuff inside of a cabinet. The other one will be mounted in a case or cabinet. I haven't decided yet what that might be. It depends on how far I take this thing.

    The instructions say it will take between 8 and 20 hours to build the kit. It took me about 6 hours to do the metal and machine work for my prototyping fixture and another 6 hours to wire everything up except for the microphone itself.

    There is building guide that is pretty good that your can down load from here; http://www.hfsignals.com/index.php/ubitx-wire-up/
    One thing to note; early in the build you wire up the power connector power up the uBITX main board, and check the current draw. If you are like me you had immediately plugged in the Radiuno module to the main board just because... but the 80 to 100 mA current draw they site in the instructions is with that module removed. It took me a little bit to figure that out.

    main board.JPG

    Front view proto board.JPG

    Rear view proto board.JPG

    At this point I built the uBITX pretty much stock except the kit's main board standoffs were replaced with taller ones so that I can accommodate a 20 character by 4 line or the Nextion 3.5" displays.

    2004A display.JPG

    I replaced the mini stereo CW key jack with 1/4 mono phone connector. The BNC antenna connector was replaced with a standard SO-239 connector and wired to the main board via RG-174 coax cable instead of the wired connector that comes in the kit. Lastly, a momentary contact button was added next to the tuning knob to make getting in and out of the menus easier.
    KK5R and KC8YLT like this.
  3. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Next it was time to power on my uBITX prototype and see what happens. It works! At least on receive anyway. I hadn't made the microphone yet.

    Once the transceiver had passed the trial by smoke test I started playing with the radio but it doesn't take long when I find four things that I want to address. The very first thing that I did was upgrade the stock firmware that comes loaded on the Raduino with firmware from Ian KD8CEC. The version that I am using at the moment (v1.095) supports the Nextion family of color touchscreen displays.


    With the upgraded firmware loaded the other three issue are next to be addressed.

    firmware 1.095.JPG

    1. The audio amplifier can barely drive a speaker. There isn't enough volume (know issue with the newer main boards.
    2.. The digital display is off frequency by 1.1Khz
    3. This little radio could really use AGC.

    Thus starts the modifications and enhancements.
    To be continued....

    K9CPO, KK5R and KC8YLT like this.
  4. K9STH

    K9STH Ham Member QRZ Page

    Be VERY careful and not let the final amplifier heat sinks touch ground. At least with the earlier versions if the heat sink got grounded the transistor would blow. This can be avoided if an insulator is placed between the transistor and heat sink with the attaching machine screw insulated from the transistor. I have no idea why this was not done. My suggestion, to the design team about this, was rudely dismissed! Just a couple of cents more in production cost would save a lot of the final amplifier transistors from destruction!

    I do have an earlier model and it works as advertised. There is plenty of audio power to drive a small speaker that I have included in the cabinet.





    Glen, K9STH
    K9CPO, KK5R, W1TRY and 1 other person like this.
  5. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Boosting the audio output was an easy fix. I used one of the little LM386 audio amplifier modules that are available of eBay for less than a $1.50.00 including shipping. It is currently powered by the 12 volt supply but I am thinking of tapping the 5 volt regulator on the Raduino module because I now have PLENTY of volume.


    Audio amp module.JPG

    Calibrating the digital display was a different matter. I spent hours and hours across several days trying to bring the frequency shown on the display closer to the actual frequency of the signal that I was receiving. Apparently I am not the only one that has had this problem.


    I tried the zero beat against WWV method but there is some other signal getting into this radio that rides right on 10Mhz making it really hard to hear the WWV signal. Weird, but I don't have this problem on any of my other radios. Next I tried using my 10Mhz rubidium standard but had the same issue as using the WWV source. Fine! Lets try 7.200 Mhz from my signal generator. I set the band on the uBITX to LSB and 40 meters, tune the transceiver so that the received signal is the loudest then enter the setup menu. I go to the Calibration Menu and zero beat my radio against the Rigol signal generator. It zero beats fine. I can get to within 600HZ difference between the displayed frequency on the uBITX and my 7.200Mhz signal source but all other attempts to close that gap by zero beating the two again results in a worsening condition sometimes as much a 3Khz differential.

    I learned early on that when you calibrate the uBITX master oscillator or the BFO frequency you have to reboot the transceiver for your adjusts to take effect. I did that but still wasn't getting satisfactory results. Scratching my head for awhile I finally tried the "Brute Force & Ignorance" approach. I tuned into one of the 40 meter nets, went into the calibration menu and slowly made changes to the cal value to tune off of frequency. For example; say that the net is on 7.178.00Mhz but I hear them clearly when the digital display on the uBITX reads 7.176.80Mhz. A positive value calibration number, say a 6 for example, moves the received signal down in frequency. A (-6) calibration number would move the received signal up in frequency. In this case I would turn the tuning knob clockwise so that signal that I am listing too shifts down in frequency. Not a lot, just enough to perceive the audio pitching down in tone. You push the PTT button to lock in the change then power the radio off and back on and re-tune. The displayed frequency on the uBITX should have move up for best audio quality meaning that the gap between the displayed and received frequencies is closing. Keeping repeating the procedure outlined above until you get get as close as you can. In my case I am now down to a difference of 10hz on 80 meters and about 30hz on 40 meters.

    Just for grins I checked the Raduino on my other kit and the differential is about 50hz so I am not touching it.

    My advice to you is if the digital display on your uBITX is within 20ohz of the received frequency don't mess with it. Unless you are OCD then you can't help yourself.

    KK5R, KG5RKP and KC8YLT like this.
  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello Glen,

    Duly noted. Thank you sir.

  7. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    With 3 of the 4 issues addressed I made up a microphone with the mic element from the kit and put it on the air last night. My first contact was with a gentleman from southern Indiana. Not bad for 12 watts out on 75 meters. My QTH is in West Virginia, about the middle of the state so the little uBITX does get out. Then again this morning I used the uBITX transceiver on the 3.815 coffee chat. My signal reports ranged from 55 to 57 with comments as to how good the audio sounded. Cool.

    This old RadioShack microphone has been in my possession since I was in high school and I finally found a use for it.

    RS mic front.JPG

    RS mic inside.JPG

    RS microphone wired.JPG

    RS uBITX mic.JPG

    BTW the measured power output into a 50 ohm dummy load on the individuals bands is as follows.

    80 meters: 12 watts (3.8Mhz)
    40 meters: 6.5 watts (7.2Mhz)
    20 meters: 10 watts (14.2Mhz)
    15 meters: 7.2 watts (21.2Mhz)
    10 meters: 5 watts (28.800)

    Strange that the 40 meter band shows a significant drop in output power compared to 80 and 20 meters. I swapped main boards from my other kit and it does the same thing. Hmmmm.

    Next I connected the spectrum analyzer to the output of the uBITX transceiver and took a look. All bands are clean harmonically speaking with all spurious signals well down below 43 dBs except for 80 meters. On 80 meters the third order harmonic is only 39 dbs down from the fundamental frequency. I swapped main boards again and the other board exhibits the same behavior. Hmmmm again.

    I need to look into that but otherwise I am pleased with the its performance.

    On to the AGC mod.

    SM0NTK and KC8YLT like this.
  8. K9STH

    K9STH Ham Member QRZ Page

    With the original unit, the microphone cartridge supplied did not have enough audio level to get much power out. I ended up building a small preamplifier powered by a 9-volt battery into an old Uniden commercial two-way microphone housing. Styrofoam was used to hold the cartridge in the center of the front housing.




    Glen, K9STH
    SM0NTK and KK5R like this.
  9. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hi Glen,

    Yes sir, a mic preamp with gain control is on my list of circuits to build and test for this project.

    Do you happen to have a spectrum analyzer? If so can you look at the 80 meter band and let me know what your second and third order harmonics look like.

    Thank you
    KK5R likes this.
  10. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    I started working on the AGC circuit yesterday and finished populating the postage stamp circuit board this evening.


    I purchased this kit from Kees Talen (K5BCQ) and it is based on Donald Cantrell's (ND6T) design.

    Unfortunately Kees no longer makes these surface mount kits but I have heard that someone else will be selling something like it soon.

    This little kit works with or without a manually adjustable RF gain control potentiometer that ND6T discusses on his website. In the version of firmware loaded on my Radunio (v1.095) there is software controlled attenuation. The two are not the same thing so I will be adding another knob to the my uBITX prototyping test setup.

    Tomorrow afternoon I will be getting my left cornea scrapped prior to cataract surgery later this fall so will be working with one eye for a while. I don't know how it will effect my ability to work on this project but it should be interesting none the less .

    KK5R and KK4CUL like this.

Share This Page