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 all,

    It's been a while since I have spent time on my uBITX project. Summer arrived and it was time for outdoors activities. However, there are several things still on the "To Do" list that I will take up again coming this fall.

    * build a Power/SWR indicator for the uBITX
    * put everything in a case with the capability for battery and AC power via a external power supply. Also make the portable uBITX so that it can be docked to a base station with a 100 watt SS amplifier built in, an internal power supply to power the amplifier and the uBITX. Maybe even an integrated automatic antenna tuner.
    Speaking of antenna tuner, that was another thing on the list. A small portable antenna tuner for field use.

    A while back the guy that turned me on to the uBIT platform told me that he had successfully made several Z match low power antenna tuners based on those cheap Chinese QRP antenna tuner kits sold on eBay and Amazon. So I thought I would give it a try. The particular Z-match antenna tuner that I was going model mine after is based on the NorCal BLT which is now kited by Pacific Antenna http://www.qrpkits.com/blt_plus.html

    The first thing was to buy the Chinese QRP antenna tuner kit.

    eBay QRP antenna tuner kit.JPG

    Looking at the parts in the kit I figured that I would only need these items.

    QRP antenna tuner parts.JPG

    Turns out that the two Polyvaricons didn't have enough capacitance to tune anything lower than 20 meters. The kit provided Red Toroid didn't look quite right compared to the Fair-Rite T106-2 that I already had in stock. Sure enough winding the same number turns on each resulted in an inductor made from the kits toroid with half the Q compared to that made from the Fair-Rite toroid.

    QRP tuner toroids.JPG

    I wound the rest of the inductor using the Fair-Rite Toroid and enamel coated wire from my stash of such.

    Even the kit provide knobs were a problem to mount securely to the two variable capacitors. I gave up on them and used my own knobs.

    So now I am down to just the SWR detector PCB, the components that populate that board including the DPST switch, the banana plug jacks, and the two BNC panel mount connectors.

    I had to come up with two Polyvaricons with enough capacitance and luckily I had them ( https://www.mikeselectronicparts.com/product/variable-capacitor-335pf-20pf/ ), knobs, a metal case, two additional switches, and the before mentioned toroid for the matching circuit itself.

    In the end my little Z-match antenna works great and I can even tune down to the middle of the 80 meter band even though the circuit, as designed, is only suppose to cover 40 through 10 meters.

    QRP Z-match antenna tuner.JPG

    QRP antenna tuner front view.JPG

    QRP antenna tuner rear view.JPG

    QRP antenna tuner inside view.JPG

    A Z match antenna is very quick and easy to tune plus there is no band switch to mess with. It makes a great addition to the uBITX transceiver but save yourself the hassle. Just purchase a kit from QRP Guys, Pacific Antennas, or QRPme.

    W6JJZ and N1OOQ like this.
  2. W0VRA

    W0VRA Ham Member QRZ Page

  3. N8OHU

    N8OHU Ham Member QRZ Page

    Looks good, Ripley. Seems that's the next thing I'll need to build after I finally complete mine.
  4. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello Arvo,

    Thank you sir. I have heard of the Antuino but didn't check in to it because I already have a very nice RigExpert Zoom antenna analyzer. It has severed me well.

    Thank you Matt. There are several places that you can get Z-match antenna tuner kits. Most are designed to tune the 40 through 10 meter bands but depending on the antenna you might be able to tune the mid to high end of the 75 meter band. At least I could tune most of my Alpha-Delta CC and it has a pretty narrow band width on 80/75 meters.

  5. N8OHU

    N8OHU Ham Member QRZ Page

    Ripley, did you go with an audio AGC or RF one? I'm too lazy to go back through the thread right now to find out. I'm looking at the one sold by Kit Projects for mine.
  6. KD8UYQ

    KD8UYQ Ham Member QRZ Page

  7. N8OHU

    N8OHU Ham Member QRZ Page

    That's basically the same as what I'm getting. Mine should be in today, and I will add it to the list of things I am installing in my radio in my own thread.
  8. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello All,

    The Covid-19 situation in the state has most of us staying home and looking for things to do including yours truly. After working through several other electronic projects that have been pushed to the side for in some cases several years, I turned my attention back to the uBITX. It's still in a test bed state so while it is why not add a few more functions. In this installment I built a LED bar graph power meter.
    The idea came from Ian's (KD8CEC) website, http://www.hamskey.com/search?q=Power+meter
    He has the RF sensor feeding the reflected power signal back to the Raduino to display SWR on a Nextion touchscreen. I decided to take the forward and reflected signals and drive a simple LED bar graph display instead.

    The first thing was to make the "Stockton Bridge" RF sensor.

    Stockton bridge.JPG

    I tried to make it as small as I could using thru hole components.

  9. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Next I bread boarded the LED bar graph meter based on the LM3914N LED driver IC.

    LED bar graph bread board.JPG

    Once again lots of information on the internet about this chip and circuit. I used this for the basis for my design. https://learn.sparkfun.com/tutorials/dotbar-display-driver-hookup-guide/all

    In my particular case I am using 5 volts to power the circuit which gives me ample overhead to accommodate the 3.2 volt signals at max power coming from the RF sensor. The 10K trimmer pot is used to adjust the input signal feeding pin 5 of the LM3914N. The fixed resistors are 1.2K and 2.2K ohm to set the reference voltage for pins 7 and 8.

    Once I got it working I made the LED bar graph power meter board. Everything was point to point wiring.

    LED power board.JPG

  10. KD8UYQ

    KD8UYQ Ham Member QRZ Page

    Hello Again,

    Here is a picture of the "Stockton Bridge" RF sensor and LED power meter mounted on my uBITX test bed.

    Stockton bridge & LED power meter.JPG

    As you can see the RF sensor fits neatly above the right hand corner of the uBITX main board. It is suspended between the Molex connector and the SO-239 connector for my antenna. The power meter board is situated to the right like so.

    In the next picture I have the 10 turn trimmer pot adjust so that it lights all five LEDs at maximum power. In my case it is 15 watts on 80 meters into a 50 dummy load.

    Power out.JPG

    Now in this picture I have my antenna connected and am transmitting on 3.815 MHz. Normally on dry days my Alpha-Delta is resonate at this frequency but today its rainy and the resonate frequency moves down the band.

    Power out and SWR.JPG

    I have the red LEDs representing reflected power calibrated such that when two LEDs are lit a SWR of 2:1 is indicated, three red LEDs roughly equals a SWR of 3:1 and so on. An open connection lights all for green and red LEDs


    It took about 15 hours over a week to build and test everything and I am very pleased with the results. When I finally get around to building my portable rig I will make the bar graph power meter smaller by using SMD components.

    Stay Safe.


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