Radios

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uBITX QRP Transceiver - March 27, 2018

Last year I assembled a BITX40 QRP transceiver from a kit and it turned out well. For under $60 it is a surprisingly good 40 meter radio. Now it has a big brother that adds more bands, more power, better performance, more features, and is still incredibly affordable. It’s also easier to build.

The uBITX is much more than just a multi-band BITX40 (the uBITX covers 80-10 meters); the receiver is much more refined and the difference between the two is not subtle at all. The uBITX has much cleaner audio and sounds more like a commercially available radio than the BITX40. It also tunes like one with a proper encoder for tuning instead of a potentiometer. To access the various modes and features of the radio there is a clever menu system that makes use of the encoder’s built-in pushbutton for navigation. Like the BITX40 before it, more advanced firmware (firmware upgrade instructions) has been developed for the radio’s microcontroller and a ton of features have already been added (Rig Control, IF Shift, CW keyer, memories, band limits, WSPR, and many more).

The amount of improvements implemented in the uBITX are especially evident in the assembly process. Where the BITX40 had many individual connections between components and the pre-assembled boards, the uBITX needs only four: power, antenna, audio, and digital. This makes wiring the uBITX a much simpler process than its predecessor. The one added complexity was aligning the screen with the cases front faceplate since the screen’s header now plugs directly into the main board instead of using a cable.

My uBITX build is similar to that of my BITX40. I used the same style case made of shielded ABS plastic with aluminum end plates (Hammond 1598RDBK) and a top mounted speaker. Due to the additional band capabilities and other upgrades the main board is about a half inch bigger in each dimension. This small change required me to use a different case model from my previous build.

The case’s removable end plates and the socketed board connections make it very easy to assemble & disassemble the radio. I kept the wiring as short and tightly bundled as possible in addition to using small coax for the antenna connection to try to reduce interference. Beyond the standard controls and connections I added a power switch, used a USB panel mount extension to provide easy access for firmware updates & rig control, installed a pushbutton in place of a CW key jack to use as a tune button, and upgraded the volume pot & audio jacks to higher quality versions than those supplied. This also allowed me to use the volume and tuning knobs that I liked. The headphone jack is wired such that it cuts off the speaker when headphones are plugged in.

If you want to build a simple, but still perfectly usable radio the uBITX is absolutely the way to go. It offers many more features and vastly improved performance over the BITX40 for less than twice the price at $109.

Update – Two Simple Mods (January 2019)

Sources for tons of uBITX mods and upgrades

• http://www.hamskey.com/search/label/uBITX

• https://ubitx.net

• Audio Pop Fix – Solves the issue of getting a blast of audio static from the speaker when switching from receive to transmit. This fix has been incorporated into the new v4 circuit boards (v4 schematic), but since mine is an older v3 board (v3 schematic) I did the mod myself. I followed the guides here, and here and mounted the parts directly to the board similar to the latter example. What I like about this method is that everything fits on the main board so final result is fairly clean. This mod involved drilling a hole in the board and scraping off some of the insulating film on the bottom, as well as exposing a few traces on the top side of the board. The mod works perfectly and looks more tricky than it is if you take your time. Be careful to get the orientation of the transistor correct since different parts have different pin-outs.

• Increase Mic Gain – The default microphone gain is inadequate for the three different mics that I have tried. I could never drive the transmitter properly with a normal speaking voice. This super simple mod definitely improves the microphone response and is highly recommended if you have poor microphone response, even on the new v4 boards which do not incorporate this mod. There are more complex microphone mods around but this one works well and only involves replacing two resistors.

BITX40 QRP Transceiver - September 23, 2017

The BITX40 is an interesting project. It is an inexpensive ($59) QRP 40 meter band SSB (LSB only) transceiver that comes as a semi-preassembled kit. The main boards are built and tested by the manufacturer in India and the end user only has to mount the boards in a case and wire the power, controls, and antenna connections. The radio itself is controlled by an Arduino microcontroller using a version of the Raduino firmware and a digital synthesizer chip provides frequency stability. Due to its simple design it is easily modified and there are dozens of mods on the internet that can be performed to add features. My ham radio club did a group build project of this radio and we had over 20 members put together their own BITX40.

One of the most convenient features of this kit is that the main boards make use of connectors to simplify construction. This also makes the radio very easy to disassemble since nearly all of the wiring can be unplugged. The kit comes with all the parts you need (other than a case, speaker, and knobs), however, I made a few changes. I had a couple of 6mm shaft knobs that I wanted to use that did not fit the potentiometers that were supplied. I also wanted to implement a couple of the simplest and most useful mods. I ordered the following parts from Mouser:

• 10K Audio Pot with Switch (Volume & Power)

• 10K Linear Pot (Tuning)

• Shielded Plastic Case

• Case Tilt Bail/Handle

• Black Pushbutton (Spare)

• Red Pushbutton (Tune)

• White Pushbutton (Mode)

• 100pF Capacitor (2nd harmonic suppression)

The pushbuttons are useful due to the features added in the modified Raduino firmware. With the new firmware installed, the white pushbutton serves as a Menu button that provides access to the additional features included in the firmware (Multiple VFOs, RIT, Split, USB, CW, frequency calibration, scanning features, and many others). One of the interesting things about the firmware is that if you have it installed and do not add any buttons or other mods, it still behaves like the default firmware. Only when you perform the appropriate mods does the additional functionality become accessible.

Another mod I performed allows the red pushbutton to serve as a Tune button. When pressed the radio automatically switches to CW mode, keys the transmitter, and generates a tone to allow tuneup of an antenna tuner. This functionality actually requires 3 separate mods (PTT Sense, CW Carrier, and TX-RX) which are detailed in the updated firmware’s documentation. They involve soldering a couple of resistors to specific locations on the board as well as a transistor across the PTT line and wiring from these components to the Arduino’s IO points. In order to maintain my ability to easily disassemble the radio by removing the case’s front and rear panels, I used a 2 pin header to create my own connectors for plugging and unplugging some of the additional wires that were added for these mods. The final modification involved soldering a 100pF capacitor in parallel with the inductor L7. This helps suppress the 2nd harmonic to levels that are acceptable to the FCC.

For the speaker I drilled some holes in the top of the case to let the sound out and mounted the speaker. I left the wires long so that it is easy to remove the top of the case and lay it to the side without having to unplug the speaker cable from the main board. Using a speaker is highly recommended for this radio instead of using headphones. This is due to the fact that the BITX40 has no AGC (although there are mods to add one) and consequently the audio from strong stations is drastically louder than weaker ones. This difference in volume could easily hurt your ears if you were wearing headphones.

An electret microphone element is provided with the kit and I wired it up with a pushbutton in a small enclosure to work as a hand mic. I secured the mic element and the shielded cable using hot glue. This arrangement required me to wire the mic and PTT lines to the same 1/8″ stereo jack on the front panel, even though they have separate connections to the main board. As basic as this setup is it functions well and I have had good audio reports on the contacts I have made using it.

The best word to describe using the BITX40 is funky. After years of using modern complex transceivers, the BITX is almost shocking for how simple it is. You tune around and adjust the volume, that’s about it. Nevertheless it works, as long as you abide by QRP operating procedure: find the strongest station on the band and weight for them to call CQ or QRZ. It’s pretty impressive how simple this radio is and how little you really need to make contacts.

I put a fair amount of effort to construct this radio carefully, however, some of my ham club’s members who built their own ended up with a spaghetti of wires and their radios still functioned fine. Because all of the complex circuitry is pre-assembled and tested, the hardest part of this project is already done. That is a key part to this being a great project because it allows people of all skill levels to build something and be virtually guaranteed that at the end they will have a working radio. In my club we had people who had never soldered before build this radio (with plenty of guidance) and they were all smiles when we powered up their creation the first time. The combination of affordability and functionality make the BITX40 an amazing piece of technology and a fantastic addition to ham radio.

mcHF – Calibration - March 16, 2017

After performing several hardware upgrades to my mcHF I upgraded to the most recent firmware release which included a lot more calibration options than were previously available. The firmware developers have also massively improved the quality of the documentation over the last six months and I decided to re-calibrate my radio from top to bottom.

The Adjustment and Configuration Manual page of the mcHF Github Wiki lays out in a very straightforward way all the steps necessary. I performed the following calibrations:

• PA Bias

• 5 Watt Power Level

• Full Power Level

• RF Power Meter Adjustment

• TX IQ Adjustment (Manual)

• RX IQ Adjustment (Automatic)

• Frequency Calibration (RX Method)

For the PA Bias calibration I found that my previous bias had been too low (400mA transmit current rise instead of 500mA), which limited my power output. With the bias properly set this time I was able to get much more power output on all bands.

To set an accurate 5 watt power level I wanted to use a power meter calibrated for this purpose since my regular meters are meant for higher power transmitters. The meter I used is a MFJ-813 which is intended for QRP use. With this meter I set the 5 watt power drive for each band and adjusted the RF power meter of the mcHF to match. Since the transmitter amplifier was now properly biased I was able to easily achieve 5 watts of output on 80-10 meters.

For the full power setting I only wanted to achieve a solid output value higher than 5 watts. To this end I only adjusted the power drive to 10 watts output for 80-15 meters, even though I could have driven it further. On 12 meters only about 8 watts was available without over driving the amplifier and on 10 meters only 6 watts. Even so this is still much better than my previous configuration which was improperly biased. This is also more power than I expected since my kit uses the standard configuration of output transformers and inductors. There are many different mods suggested by other mcHF builders to increase the power output, however, for me 10 watts on the most commonly used bands is more than enough.

The TX IQ adjustment was an interesting process involving listening to a tone generated by the mcHF on a second receiver tuned to the opposite side band. I was able to mostly null out the tone using the IQ phase and balance adjustments. While not perfect I am sure that it is better than the default settings. The RX IQ is automatic and only requires turning on the firmware setting in the menu.

Frequency calibration was also an interesting undertaking since I was using the RX method which requires a stable shortwave source to lock on to using synchronous AM. I adjusted the ppm of the receiver using three different strong stations and achieved similar results with all three so I am confident that my setting is much more accurate than the default value.

mcHF – New Case - March 10, 2017

I have had my mcHF for almost a year and after seeing some of the better cases available for it I decided to move on from what I had been using. Many members of the Yahoo group have used the so called “Chinese Case” which is made of formed aluminum and comes with all of the knobs, buttons, speaker, shield plate and mounting hardware necessary to put it all together. It also features nicely screen printed labels for the buttons and ports and a good overall fit and finish. I purchased one of these cases on eBay for about $150 and it took a week and a half to arrive from China.

Overall this case is fantastic! I wish I had purchased one of these when I was first building my mcHF. The vast majority of the assembly process went very smoothly, however, I did have to make a few modifications to both the case and my mcHF.

The assembly of the case is done from the back to the front. First I mounted the speaker to the case’s back plate. Then I slid the RF board into position along with the top and bottom auxiliary plates which serve as mounting points for the other case panels. The radio is then assembled as a sandwich of RF board, shield plate, and UI board using the 2.5mm screws and standoffs.

The case requires a very specific alignment for the positioning of the amplifier MOSFETs and the power regulators regarding how far they are mounted from the RF board’s surface. For my kit, the amplifier MOSFETs were perfectly positioned to align with the mounting holes, but my power regulators were a couple of millimeters too close to the board. After debating repositioning the regulators I decided instead to enlarge the screw holes and just make it work. This was accomplished with a 3/16″ drill and a small file. In the end I didn’t maul the case too badly and all of my work is hidden behind the small washers I used with the #4-40 screws that secure the devices to the case’s surface for proper heat transfer. I also had to modify the end panel with the USB and BNC ports. The alignment was slightly off and I had to enlarge the hole for the BNC a little bit using my nibbler tool and a file in order for the plate to fit over the ports properly.

Another problem that I ran into was the depth of the tactile switches supplied with the kit. The actuator for the switch is too long to allow the case to be close properly. Fortunately this type of switch comes in a variety of depths and one of the Yahoo group members had posted last year about a substitute part that works with the Chinese case. I ordered some from Mouser (CTS 222AMVBBR) and installed them on the UI board. The new switches are not only the correct depth, they are also smoother to operate. When combined with the rubbery buttons provided with the case, the operating feel of the radio is much improved from the plastic buttons and stiffer switches that I had been using.

This case is a huge upgrade over the previous one. It is better looking, better constructed and more securely holds the mcHF. I also love that the case features an internal speaker (which sounds surprisingly good) and a kickstand to prop the radio up at an angle for more convenient ergonomics. The finished case weighs 21.5 ounces, which is slightly more than the old case, but it is still very lightweight. I didn’t use the knobs that came with the case as I like my previous upgrades better, however, that is the only aspect of the case that wasn’t an improvement. This case is definitely worth the money and even though it is more than double the price of my old case the radio-case combination still costs well under $600.

mcHF SDR Transceiver Kit - June 8, 2016

A huge part of the history of ham radio involves people building their own equipment. In fact that is how things started since at the beginnings of radio no commercial hardware was available. Over the years various companies and organizations have sold transceiver kits, but in recent years most of these have consisted of basic morse code only or single frequency single side band devices intended for digital communications. With the increased development of software defined radio (SDR), however, this is changing. Earlier this year I came across the mcHF SDR transceiver project and decided to purchase one of the kits. Unlike other basic transceiver kits the mcHF is a full featured radio with 80M-10M coverage, multi-mode support, variable bandwidth filtering, DSP (noise reduction, notch filtering, etc.), sound card interface, rig control, and band scope / waterfall capability. Not bad for a $388 kit.

The project was originated by Chris, M0NKA in the UK about 2 years ago and the design has gone through a number of revisions resulting in the current v0.5, which is what I purchased. One of the major reasons I was willing to undertake this project was that the kit offered by Chris includes the circuit boards already populated with about 95% of the surface-mount parts, including all of the tricky to solder chips and super tiny resistors and capacitors. The only remaining parts to install are larger, and therefore easier to solder, surface-mount parts and standard through-hole components. The builder also has to hand wind several toroid inductors and transformers. You also have to provide your own final power amplifier MOSFETs, shielding plate between the boards, and case for the radio. These requirements go along with the way this kit is sold, which is to say bare bones. The kit includes zero instructions. The builder is responsible for sorting through the mcHF downloads page, the mcHF Yahoo group, and the Github Wiki to find the details regarding how to wind the toroids and transformers as well as details on any recommended mods and instructions for how to use the radio.

Since this project is open source, both the hardware and firmware have undergone considerable development. In fact, from the time I started building the board to when when I completed the project a large firmware update was released which revised the main screen and menu layout as well as added a number of fixes and features, including the ability to control the transceiver via the USB port and detect the transceiver as a sound card device with a PC.

The mcHF consists of two circuit boards called the UI board and the RF board. I built the UI board first, and then built the power supply section of the RF board so that I could power up and test the UI board. Chris has a very helpful document on the mcHF webpage that steps through the process of installing the bootloader and uploading firmware to the CPU on the UI board. So after only about 4 hours of work I had a functional UI board.

Next I completed the remainder of the RF board, which was fairly time consuming since winding toroids and transformers is a tedious operation. Documentation exists for how to wind the transformers, however, the only information regarding the toroids is on the RF board schematic which details how many windings each core requires. Extra attention should be paid to stripping the enamel wire used for the toroids and transformers. Even though I diligently sanded off the outer coating and thought that I had solid solder connections to the board, I did not do a good enough job on two of the toroids which prevented the radio’s operation on the 80M band. After desoldering and re-sanding the wires I achieved a good electrical connection and consequently 80M functionality.

This portion of kit construction is somewhat confusing because there are a ton of possible mods for the various transformers that can improve performance of the final power amplifier. I decided to build mine in the default configuration which results in a solid 5W output on 80M-12M and about 4W on 10M. When modified, users report 10 or more watts of power output. The only modification I made was with regard to the SWR bridge where RG-178 coax is used in place of a single winding of enamel wire. Construction details for many of these mods are available in a document on the Yahoo group produced by Clint, KA7OEI who has done considerable work on both the hardware and software of the mcHF.

Although not technically a mod, I did add a resistor that is regarded as “optional” on the UI board schematic. This resistor provides power for when an electret microphone is used. Since I would be modifying an Icom HM-36 I had lying around to work with the mcHF, I needed to install this resistor in order for the microphone to function. For this I used a standard 1/4W resistor since I had on of the correct value in my junk box and just soldered it to the surface mount pads. In order to avoid shorting with nearby components I carefully shaped the resistor’s leads and used electrical tape to insulate between the parts.

After completing construction of the boards, I turned my attention to completing the radio as a whole. The first step of this was to construct the shield plate between the boards. For this I used a thin sheet of aluminum that I hand cut, drilled and nibbled according to a pattern available on the mcHF website. I then test fit and assembled the board and shield sandwich to check for proper clearance. When I was satisfied I completed the assembly using 5mm standoffs.

If you look around the web you will see a lot of people who have built the mcHF using the same case. This case is sold by Artur, SP3OSJ from Poland for about $63. If you email him at asnieg@epf.pl he will give you the details for how to order. The case comes with all of the knobs and buttons as well as a small piece of acrylic to protect the LCD display. The front panel is pre-machined, however, the endplates are left to the builder to complete. I also had to file some of the button holes to allow smooth operation and I had to sand the acrylic to fit the opening in the case.

Since the case serves as the heatsink for the power supply circuitry as well as the final amplifier transistors, a good mechanical connection between the components and the case is necessary. To accomplish this I soldered brass #4-40 nuts to the heatsink fin on power supply and amplifier components. I then drilled holes in the case to match where these nuts line up when the case is assembled. When bolts are inserted and tightened, the electrical components are pulled tight to the wall of the case. In order to achieve a properly aligned connection, I had to grind away a small amount of material where the final amp transistors contact the case (note the hole I drilled in the wrong location due to my inability to follow the old rule of measure twice drill once). The last step in construction was labeling the buttons and ports, which I did using vinyl self-adhesive labels and my laser printer.

The final adjustment before testing the transmitter involves setting the proper bias for the final amplifier and then setting the transmitter gain for each band of operation. Documentation for these adjustments is on the Github Wiki. Basically you set the bias in one of the mcHF’s menu settings while keying the transmitter with no audio present as you watch the current draw of the radio. The transmitter gain is also a menu setting. These adjustments can be accomplished with an ammeter and a RF power meter.

Finally, after about 20 hours of work I put my mcHF on the air. After adjusting my microphone gain I made a contact on 40M SSB. I then plugged the transceiver into my PC and fired up WJST-X. Following the guide on the Github Wiki I was able to get rig control working and made a half dozen contacts using JT65 on the 30M band using nothing but the mcHF and my laptop. The next day I checked into my local 10M SSB net and received good signal and audio reports from the other regulars who are familiar with my voice.

Overall I have to say that I am incredibly happy with the mcHF kit. It has been a great learning experience and the radio itself is an incredibly capable and configurable device that offers a lot of bang for your buck. I plan to use the mcHF quite a bit in the future and look forward to any future firmware updates. I also hope that this kit leads to other similar kits in the future that can help get more hams back to building equipment.

I highly recommend this kit for anyone with some electronics experience. While the documentation has not been collected into one easily digestible package, the kit itself is actually very straightforward to put together and I was able to get it on the air with only a cheap multi-meter and an RF power meter. It is also an incredible bargain for such full featured radio; I spent under $500 total for the kit, case and other ancillary parts (not including the microphone) which is not bad at all when you compare this to what is available commercially.