The uBITx Transceiver Kit

Discussion in 'Amplitude Modulation' started by W8KHK, Dec 27, 2019.

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  1. W8KHK

    W8KHK Ham Member QRZ Page

    Christmas came a couple days late when DHL pulled up in my driveway this afternoon and delivered a new solid-state transceiver "kit". While this is not an "AM" rig, my plan is to make it the control center of my entire HF AM station. That said, an explanation is in order, but first I will share some details about the product.

    The rig is called uBITx, (Micro-Bit-x) by the QRP hacker community. The brainchild of Ashhar Farhan VU2ESE, It is based upon open-source code (GitHub) and a large community of QRP enthusiasts. Visit http://ubitx.net/ for a wealth of information. Everything in this post is based upon what I have learned while reading forum posts and studying the schematic and source code.

    The transceiver operates on CW and SSB from 3 to 30 MHz. It is a synthesized rig based upon the Arduino "Nano" microcontroller. Three variable frequencies are generated by the SI-5351 DDS chip, providing mixer and BFO inputs for double-conversion on both receive and transmit. Transmission is enabled on the standard amateur radio sub-bands, however receiver operation is general coverage throughout the entire HF spectrum. When transmitting in CW, a single DDS oscillator is used, no mixing is involved. Power output is nominally ten watts, although somewhat lower on 15 meters and above. The output circuit employs a pair of IRF510 MosFets in push-pull, driven by four 2N3904's in push-pull parallel. There are absolutely no unobtanium parts used in the rig, therefor it should be easy for any ham to repair or modify, as desired. A tag line on their web site reads "....just waiting to be modified." I have reviewed the source code, all written in C for the Arduino, and it is well structured and documented, such that feature additions and other mods are practical.

    I originally ordered version 5.0, which is a semi-kit, priced at $129 plus optional DHL 3-day delivery for an additional $10.. In this version, the main board and the controller/DDS/display were pre-assembled and tested, and the builder need only wire connectors and controls, and provide a suitable enclosure. They advertise shipping within 7 to 8 business days, which apparently is true. On the 6th business day after placing my order, I received an email, announcing the opportunity to upgrade my order to version 6 if desired.

    While version 5 employed a two-line, sixteen character display, version 6 uses a graphical TFT touch-screen, and all connectors and controls are soldered on the main board, with the exception of the speaker and rotary encoder for tuning and menu cruising, which are wired with plugs that mate with the main board. Total cost of the version 6 product is $199.00 plus $10 if DHL shipping is desired. It is available for $30 less if you do not desire the enclosure. The product was shipped five working days after I upgraded my order, and DHL delivered from India three days later!

    The input signal is first up-converted to 45 MHz and passed through a crystal filter. The second mixer converts to 12 MHz, using an array of 8 matched crystals in a 6-pole filter arrangement. Version 6 altered the second IF to 11.059 MHz to avoid spurs from the micro-controller. By the way, both versions include a CW keyer, implemented by the Arduino. A single port supports either a straight key or a paddle. Using a couple resistors and a single analog input port, the voltage generated by either paddle or key is decoded and automatically enables the keyer. PTT from the microphone connector automatically puts the rig in side-band mode. There is no mode switch, per-se, and USB vs LSB is automatically selected based upon frequency. It is possible, through the menu, to over-ride the standard side-band mode.

    Upon receipt, I did a careful visual inspection of the product. Fit and finish of the enclosure is excellent, much better than the typical home workshop would produce. The double-sided board is well-organized, silk screen is clear, and soldering is high quality, with no trace of rosin residue. Most of the bottom layer provides a ground-plane. The controller is a separate board that plugs into the main board with right-angle pins, while the display module and Arduino plug into the vertical controller board.

    Viewing videos on the web, I noticed that the menu response performance is not stellar, but it is certainly acceptable considering the limited power of the Arduino Nano performing all functions. Several hams have upgraded version 5 to use the intelligent "Nextion" display instead of the LCD character display. The Nextion has an embedded processor, compact flash receptacle for uploading code, and a high-speed serial interface to the Nano processor. This makes a very professional display and user interface, rivaling those seen on the big three at HRO. This mod is accomplished with a software update to the Arduino, but absolutely no mods were required to any of the hardware other than replacement of the display panel. Some folks have interfaced multiple Nextion displays to the rig.

    So back to the original question, how does this apply to my AM station? For quite some time I have been working on an Arduino-based control center, primarily as a frequency source using a DDS module. Most of the software is written, but none of it is packaged or integrated. My plan is to use this transceiver as the VFO for all my AM rigs, leveraging the CW mode. Plenty of power to drive a Valiant , Viking II, or my home-brew exciter for the big rigs. Transmitter selection could be automated, in the same manner the Arduino selects the appropriate bandpass filter when changing frequency. For receiving, I could pick a signal from either the first IF at 45 MHz, or the second IF at 11.059 MHz and send it to the SDRplay RSP-2, for true transceive operation. Another option is to build a separate 11.059 filter, not quite so narrow as the six-pole filter in the transceiver, and feed an infinite-impedance detector, or possibly a synchronous detector. I ordered and received a batch of crystals for the low IF filter at five for a dollar! So much of what I envisioned building from scratch is already completed in this hardware and software package!

    I will post some pictures of the kit as-received, and a couple from the web showing the un-modified version 6 TFT display, as well as the user-mods ting the intelligent Nextion display. As I move deeper into hacks and feature additions, I will post them in the future.

    20191227_151119.jpg
    Front view of main board with the controller and display attached.

    20191227_151152.jpg
    Modules separated showing connection method.

    20191227_151138.jpg
    Top view of assembly. The Arduino NANO is plugged into the back of the controller board. This combination of modules is known as a Raduino.
     
  2. W8KHK

    W8KHK Ham Member QRZ Page

    20191227_151440.jpg This is a view of the main board.....

    A single 45 MHz crystal filter in the center, and a row of eight 11.059 MHz crystals forming the 6-pole filter at the bottom left.
     
    Last edited: Dec 27, 2019
  3. W8KHK

    W8KHK Ham Member QRZ Page

    A few more photos....

    20191227_151351.jpg

    The kit of parts as received

    20191227_151315.jpg

    The enclosure
     
  4. W8KHK

    W8KHK Ham Member QRZ Page

    These photos are from the website.....

    cropped-cropped-ubitx_v6_big-768x450.jpg

    The version 6 with the graphical touchscreen display, unmodified.... as received today...

    cropped-ZL1AXG-uBITx-with-Nextion-Display-1.jpeg

    The version 5 with a custom enclosure and the Nextion Intelligent display..... Version 6 may also be updated to use one or more Nextion displays instead of the TFT display shown in the previous photo...

    The controller software will simultaneously support multiple Nextion displays of various sizes over the serial interface. This allows remote displays, as well as multiple screens with different information on each screen.
     
    Last edited: Dec 27, 2019
  5. N2DTS

    N2DTS Ham Member QRZ Page

    I built a few bitx 40 rigs, a few because I fried the cpu trying to get it to work right.
    A really marginal radio, above some power level the TX audio went digital, and tuning the radio in RX had loud clicks in the audio every change in frequency.

    In an effort to quell the loud clicks I blew out the display/vfo part. Put the thing in the trash.
     
  6. K4KYV

    K4KYV Subscriber QRZ Page

    Too bad it covers only 3-30 mc/s. 160m coverage is one of the benchmarks that a rig has to have to be in my station. The days of the "all-band, 80-10m" rigs are long gone.
     
    WZ5Q and K5UJ like this.
  7. K5UJ

    K5UJ Ham Member QRZ Page

    That's a clever idea, using it as a RF signal source (VFO) provided the FETs don't fry with continuous duty RF to drive a 12BY7 or 6AG7 for an AM xmission. The lack of 160 and AM is disappointing and I speculate that in the country of origin (India?) both are not legal. I don't believe 160 is an international allocation although I may be mistaken about that, but I know AM is not legal everywhere which is a shame. The AM haters got there way in some countries because there were not enough hams with a passion for AM to fight it like Don. On the other hand, if AM were an available mode, the box would probably be so pissweak as to not be worthwhile. But congratulations on tinkering with something instead of just buying a plastic radio at a hamfest.

    Anyway, did you populate that board? If that was necessary that would put me out right there. I can't solder SMT very well. Open source is good and bad. I spent the last 10 years of my working life in open source hell, where software is in constant flux, Git pull requests are changing procedures, Github is full of incomprehensible hieroglyphics, and decent documentation is nowhere to be found because people who develop for free can't be bothered with the mundane tedious chore of writing documentation. Then you get a package that runs on the developer's machine, but crashes on your distribution of Linux. But it is free (you get what you pay for). I just finished installing SDR# on a used windows laptop and downloaded and unpacked two plugins from Russia and that was enough for me.
     
    Last edited: Dec 28, 2019
  8. K5UJ

    K5UJ Ham Member QRZ Page

    Same here. When I got into AM, 160 m. coverage was mandatory for me. It was amazing the gotchas that were out there, such as the 75A-1 not covering 160 but the 2,3 and 4 including it. And the 32Vs not covering 160 along with the bigger EFJ rigs, while the Valiant and lower power did. I believe the 75A-1 left it out because 160 was not available when it was designed, but for transmitters, it was left off to save space and money.
     
  9. W8KHK

    W8KHK Ham Member QRZ Page

    As it stands, the transmitter only covers the bands between 3 and 30 MHz, not including 60 meters. The receiver works well below 3 MHz, and is hot on 160 Meters, as well as the standard broadcast band and below. The tuning rate is 1 KHz per step in the ham bands, 5 KHz outside of the bands. This can be modified to cover 160 at a lower rate, just by editing a table and re-compiling.

    I have little use for 10 meters, so it would be very easy to change the output filter L and C to 160 meters, and update the software to enable this filter when the tuning 1.8 to 2 MHz. I considered these things before I ordered, and had a clear plan for addressing 160, but right now I am antenna-challenged, not enough room or elevation for a decent dipole, and would need substantial radials for an inverted-L to function. Maybe in the future, but not right away.
     
  10. W8KHK

    W8KHK Ham Member QRZ Page

    This "kit" assembly required NO soldering. The only solder joints off the PC board were on the cables that connect the speaker and the tuning rotary encoder, and I found these neatly done when I opened the package. So it was a rather boring assembly task, just mounting the two boards, installing knobs, and bolting on the cover. The boards are tested prior to shipment. Assembly was completed in minutes.

    The surface mount capacitors and resistors are large, and easily manipulated if any repairs or mods are needed. Standard transistors with leads could easily replace individual SMD components. Rather than provide an adjustment for the three balanced modulators, dual-diode packages with factory-matched devices were employed in these circuits.

    As stated in my reply to Don, 160 meters will not be a problem to implement on transmit, and the receiver goes down well below the standard broadcast band. Listening to WSB at 710 KHz in Atlanta for over an hour, no drift was observed, and it would have been noticable when receiving a BC station with a product detector.

    I suppose there is no sense looking at going higher than 30 MHz, as the unit up-converts to 45 MHz first IF. I have heard none of the birdies or other noises that Brett mentioned on his bitx40, possibly because they moved the second IF from 12 MHz to 11.059 MHz. They were very careful with the routing of the three signals from the DDS on the control board to the mixers on the main board. I suppose the only problem I might encounter would be some IMD or other issues with regard to DDS output signal purity. But this would only impact receiving, as that would be lost in the tuned circuits of the AM signal path following the exciter. I was pleasantly surprised that frequency calibration was spot-on; broadcast stations, WWV, and CHU all zero-beat with all zeros at the end of the frequency display.

    As to power output and duty cycle, I looked at compatibility issues there before I ordered. The inexpensive IRF-510 output devices have moderately-sized heat sinks, but much larger ones could be accommodated, even mounting them to the back panel for external convection cooling is certainly possible. But a better option is to reduce the power level to just what is needed, and run the final in class-C. The board has three trim-pots, one for adjusting the drive level on transmit, and the other two individually adjust the bias to the push-pull IRF-510s. Since I have no intention of running a PW sideband rig, there is no need for linearity in the final. So I do not expect to see excessive dissipation during an old buzzard transmission while using this rig as an exciter.

    There are header connection traces at the input and the output of the crystal filter (second IF) so no hacking is needed to provide an output to an AM detector or SDR feed. And on AM, I would certainly not use the internal LM-386 stage to drive a speaker!

    Regarding open-source software, yes, I agree it can become a real headache with updates if you depend on others for fixes and features. But I find the code for this product to be structured, well-designed and written, with very detailed documentation, including detailed use of the variables and constants, encouraging modification. I suppose most folks would not be using their rig as an AM exciter, so I will probably just start with the baseline code and go my own way. KD8CEC has done a lot to contribute to this project, both in hardware and software, as google will reveal. He has also generated documentation in the form of user manuals in PDF, separate versions for each display type including the Nextion. One of the things I appreciate, which he encouraged and actually instigated, is making mods to the software that DO NOT require hardware alterations, and most important, the preservation of other's code contributions, rather than blatantly replacing other's contributions. After working in software for many years at HP and Agilent, it is refreshing to see this focus is also present in some user-contributed code.
     

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