BITX40 QRP Transceiver

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 most useful and simple mods. I ordered the following parts from Mouser:

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 Mode 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 and sends 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.

QRP Link Dipole Antenna

Dipole antennas are some of the simplest antennas to build in addition to being very efficient and solid performers. I wanted to make a simple dipole antenna for QRP portable operation that could be used on multiple bands. I also wanted it to be light enough to be supported by my lightweight 31 ft Jackite mast in an inverted V configuration.

Link dipoles are a great way to make a lightweight multi-band antenna because you only have one run of wire (vs a fan dipole) and you don’t need a complicated and heavy balun (vs an off-center-fed dipole). Band selection is achieved by connecting or disconnecting the appropriate links to make the antenna as long or short as needed to work on the band you want. To keep the antenna as light as possible I used 26 AWG toughcoat stranded copper-weld wire from The Wireman (#534). This wire is small, but because it has a steel core it is stronger than pure copper wire would be. It also has very tough insulation that protects the wire very well and is exceedingly lightweight (1000 ft weighs under 1 lb, and I am only using about 66 ft).

For the physical links in the dipole I used Nite Ize MicroLock S-Biners. These are small polycarbonate double-carabiners that are more than strong enough and very light. I made a loop at each end of every antenna section and secured it using adhesive lined heatshrink tubing. While not the strongest connection this should be adequate for this application since the antenna is so light that there isn’t much strain on any one point. The electrical links in the dipole were made using Anderson Powerpoles. The antenna itself was cut for the 20, 30, and 40 meter bands. I am considering adding an 80 meter section in the future, but that may add too much weight.

The center feed-point was made using a small piece of 1/8″ acrylic. This was drilled for antenna wire strain relief as well as #8 bolts for the connection between the antenna and the coaxial feedline. I decided to forego using a 1:1 balun at the feed-point to save weight. The feed assembly is secured to the mast using wire ties. Since every mast section is tapered the assembly can only slide so far down from the top before it fits tightly to the mast. I adjusted the wire ties to place the peak a couple of feet down from the top where the mast is somewhat more substantial and can more easily support the weight of the antenna. For coax I have been using RG-58, again to keep the weight down. I may end up moving to RG-8X in the future if the mast can support it since it is much lower loss.

A handy feature of this antenna is how easy it is to put up. The mast is a good match for my flag pole hitch mount (using a 2″ PVC spacer) and is strong enough to be freestanding. To erect the antenna I just have to secure the upper three sections of mast (the sections friction lock together), place the mast in the mount on my car, unroll the antenna, slide the feed-point onto the mast, connect the coax, push the rest of the mast up, and spread out & secure the antenna ends. I can be on the air in about 5 minutes.

All of my efforts to keep the antenna as light as possible definitely paid off. Together the antenna and winder weigh only 15 oz (not including feedline). This makes it a perfect match for the lightweight mast and a small QRP radio. I look forward to getting a lot of use out of this setup.

Ham Radio EMCOMM Go Kit – Solar Charging System

Field operations using batteries are very common and my battery box is a very convenient source of power. For longer term operations, however, keeping the battery charged is just as important. In order to supplement my battery system I put together a small solar charging system.

Parts

  • 50 Watt, 12V Solar Panel – Renogy
  • 10 Amp PWM Solar Charge Controller – Renogy
  • 1″ Aluminum Angle

The goal here was to have a simple solar system that would be large enough to charge my battery box at a decent rate, while still being small enough to transport easily. I also wanted to keep the costs fairly low.

I went with a 50 watt solar panel since it is fairly compact (around 2 ft square), inexpensive (about $80), and puts out almost 3 amps at peak sun. The charge controller (under $30) prevents the panel from overcharging the battery when the sun is out and blocks the panel from discharging the battery when the sun goes down. The aluminum angle frame holds the parts permanently together (which simplifies field wiring) in addition to holding the panel at a 30 degree angle. A 30 degree panel angle is a good compromise for my latitude and helps maximize the panel’s sun exposure throughout a full day. All together the panel, controller, and frame weigh only a few pounds.

Operation

I used this setup with my battery box and go kit for Field Day this year and it performed very well. I generally do digital only on Field Day and made over 160 contacts using PSK31 and RTTY with the radio set for 50 watts output. With the sun out, the panel kept up with my power usage and by sunset the battery was essentially fully charged despite me operating for several hours. I continued to operate after sunset and quit around 1AM. I resumed operating mid-morning and the few preceding hours of morning sun had recharged the battery back to near full charge.

As with any battery testing, the current draw is the deciding factor for how long your charge will last. Since Field Day is in many ways a contest I was transmitting quite a bit which increased my current draw compared to more casual operations. Overall I operated around 16 hours and never drained the battery below 12V. If I turned the power down, I could probably operate the entire 24 hours and dropping from 50 to 25 watts would have minimal impact on my ability to make contacts.

mcHF Update – Calibration

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 Update – New Case

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 Update – Touchscreen

The mcHF firmware developers have added a lot of UI functionality that uses the touchscreen, with more coming in the future. Some of these added features are simple conveniences that save the user from going into the menus to change a setting. Others are more involved and they have made touchscreen usage more of a requirement going forward. After investigating how the touchscreen could be enabled for my version of the kit I decided to go ahead with it.

Touchscreen Activation Steps v0.5

  • R30, R31, R32 should be a 0 ohm resistor (this was already done on my board)
  • R33 and R34 should be removed
  • R34 (right pad) is connected to R47b (bottom pad)
  • R33 (right pad) is connected to R47d (bottom pad)

 

 

 

 

This process was actually far simpler than I had first anticipated and can be completed in under 30 minutes. When the radio is turned on it now shows “Touchscreen: Yes” on the boot screen indicating that the touch sensor is detected by the firmware. In order to test if everything was working properly I used the Button Test function. This is done by holding down any button (other than band minus) while powering on the radio. I then drug my finger around the touchscreen and noted that it correctly read the touch input. With touch enabled it is much easier to change the meter reading as well as toggle from spectrum display to waterfall and switch between the various input methods (microphone, digital, digital iq, line in, etc.) without having to go into the menus.

WSPR Antenna Comparison (Loop vs Dipole vs End Fed)

Over the last few months I have been playing with WSPR and I wanted to be able to use it as a rough way to evaluate the relative performance of different antennas. My goal was to test how well two different antennas that I made for field use compare to my base station antenna.

Antennas

My base station’s loop skywire was tested in its current configuration, 270 feet of wire strung between several trees. The two test antennas were put up in the same configurations that I intended to use them in the field.

Test Procedure

I did 24 hour WSPR runs using 5 watts of power with each antenna on successive days. The idea was to test each antenna in as equivalent band conditions as possible. By using the WSPRnet Database, I was able to collect signal reports from every station who heard me over the 24 hours. I then put all of this data into a spreadsheet. I calculated the average, median, maximum, and minimum dB signal reports for each antenna on every band I did the test. I also generated the same results for stations within a 500 mile radius as well as within a 300 mile radius. The purpose of these additional calculations was to evaluate each antenna’s performance for EMCOMM situations. Finally I calculated the same data for the distances from the receiving stations.

Results

WSPR Antenna Comparison Data (PDF)

Conclusions

The first thing that I noticed when looking at the WSPR data was how closely the end fed and loaded dipole performed on both bands. The end fed seems to have a slight edge, but I would put this down to it being higher in the air rather than any inherent design advantage. On both bands the end fed is about 1dB better than the dipole, but given band fluctuations from day to day and the inaccuracy inherent to WSPR signal reports I’m going to call this a draw. Even the receiving station distance numbers were strikingly close to one another. This makes sense since both of these antennas are essentially identical, except one is fed in the center and the other is not.

On 80 meters the loop is clearly the best performer, besting both of the test antennas by at least 2dB overall and by several dB for regional contacts. It also reached much further out with almost double the average and more than double the maximum distance to a receiving station. Add in that it had the most spots from almost 40% more stations and it is clearly the most effective antenna.

On 40 meters the loop’s results are more complicated. Looking solely at the signal report data the loop is the worst performer of the three. I found this to be a ridiculous assertion because of how well this antenna performs in my personal experience for both regional and DX communications. One explanation for the relatively poor overall report is that the loop easily outperformed the other antennas in average and median distance to receiving station in addition to receiving 27% more signal reports from 33% more receiving stations. This could have skewed the results because more distant stations with additional spots would give weaker signal reports.

To test this idea I dug a little deeper into the data and looked at stations that heard all three antennas. What I found was that the loop generally had more spots from the same station than the other two antennas. These extra spots always came at the poorest times of day for propagation and consequently resulted in very low signal reports. When the receiving station had spots for all three antennas at the same time of day, the loop almost always had the highest signal report, usually by multiple dB. This combination of factors pulled down the average and median signal reports and masked how well the loop performs on 40 meters. I think this information also points to just how good of a performer the loop is on 80 meters because in spite of having a similar problem to overcome it still received the best signal reports by far.

Using WSPR to evaluate antennas is not an exact science and I am far from an expert statistician, so these results are by no means definitive. That said, I think this was a worthwhile exercise and resulted in some interesting data that generally correlates with my first hand experience using these antennas.

80/40 Meter Loaded Dipole Antenna

After having success with my resonant end fed antennas I decided that I wanted to build a more traditional resonant half-wave antenna that was also considerably shorter than normal. The plan for this antenna was to build a lightweight 80/40 meter antenna for field use (as part of my Go Kit) that wouldn’t overload my 21 foot telescoping fiberglass mast. The antenna also needed to be capable of handling 50 watts at 100% duty cycle for digital operation as well as 100 watts of SSB.

Design

Similar to my 80/40 resonant end fed antenna, the goal for this antenna was to achieve resonance on both 80 and 40 meters by using loading coils large enough to isolate the 40 meter element of the antenna while simultaneously greatly shortening the space required for 80 meter operation. Several vendors sell antennas of this design (MFJ, Alpha Delta, etc.), however, I always prefer to build my own since I can build the antenna exactly how I want, save money, and learn something in the process.

There are a lot of good resources regarding how to build this type of antenna. K7MEM has a loaded dipole calculator that lets you play with different parameters to determine how big the loading coils should be and how far they should be placed from the feedpoint. This works best for single band designs, but it also serves as a good way to double check antenna dimensions. I also found this design, as well as an article in the April 1961 issue of QST that both provide a great starting place for antenna dimensions and what size loading coils to use. The coils used tend to be in the 80uH to 130uH range. Larger coils allow for a shorter antenna, however, they also reduce the available bandwidth. I went for somewhat of a middle-ground with 111uH coils. Due to the antenna’s limited bandwidth I planned to use extension stubs to shift the antenna’s resonance from the top of 80 meters for voice work to the bottom for digital operations.

Construction

In order to keep the antenna as light as possible I used 18AWG stranded copper wire. The coils were wound using 22AWG enamel wire. Each 111uH coil was made using 65 turns of the enamel wire on a 1.25″ PVC form (I used K7MEM’s coil designer to figure out the details). I used stainless steel screws and 8-32 hardware to secure the enamel wire and provide a connection point for the antenna wires. I then coated each coil with two coats of polyurethane for weather sealing and to secure the coil to the PVC.

For the 40 meter elements, I first connected the two antenna halves to the center balun (I used a Unadilla W2DU 1:1 balun that I had laying around). Then I connected the other end of the wires to the loading coils. The short 80 meter elements were then wired to the other side of the loading coils. The 40 meter elements were trimmed for resonance at 7.1MHz which resulted in a span of about 67.5 feet for the 40 meter section.

I then began trimming the 80 meter elements. While there is minimal interaction between the 40 and 80 meter sections of the antenna due to the choking effect of the loading coils, when the 80 meter section is trimmed is does slightly effect the 40 meter section’s resonance. For this reason the 40 meter section was left a little long so that when the 80 meter section is the correct length, the 40 meter section resonates on the desired frequency.

After trimming, the 80 meter elements were about 4 feet long for a total antenna span of about 76.5 feet (including the coils). This resulted in resonant frequencies at 7.15MHz and 3.977MHz. I found that by adding 18.5 inch stubs (using Anderson powerpoles) to the end of the antenna resulted in a resonant frequency of 3.583MHz. The 40 meter 2:1 SWR bandwidth effectively covers the entire band. On 80 meters the antenna has about 40kHz of 2:1 bandwidth and 60kHz of 3:1 bandwidth. One major advantage of this antenna over my resonant end fed is that it does not use any complex matching system, only a 1:1 balun. This allows for more aggressive use of an antenna tuner without the risk of damaging the matching system, which increases the usable bandwidth of the antenna. Using the internal tuner in my Yaesu FT-450D I can increase the antenna’s 80 meter 2:1 SWR bandwidth to about 130KHz.

This antenna turned out about as well as I had hoped it would. With the winder it weighs only 3lbs, 1lb less than my 80/40 end fed. It is also a very good match for my Go Kit’s fiberglass mast as this combination held up well even when loaded down with some ice and snow and with wind gusts over 30mph. The loaded dipole makes a nice balance between size and performance and will be my Go Kit’s primary HF antenna going forward.

Boafeng UV5R USB Soundcard Interface

I recently purchased a Baofeng UV5R5 to throw in my Go Kit as a backup handheld and I decided to build an interface to be able to send and receive digital signals. The interface was intended to be as simple and inexpensive as possible, much like the radio itself.

VHF/UHF digital EMCOMM transmissions in my area typically use the MT63 mode which is very robust and can work quite well using only acoustical coupling. While this technique works surprisingly well, it has limitations. If the area you are operating in is too noisy, your audio is too weak, etc. the data transmission can have issues getting through correctly. It also doesn’t work very well for modes other than MT63.

USB soundcard interfaces are very common, I have multiple SignaLink USBs myself, but they are definitely overkill for this application. After some experimentation, I built this simple interface for under $20.

Parts

Construction

The main idea for this project was to replace the external speaker microphone functionality with that of the USB soundcard. In order to do this I used the speaker mic cable and wired it to two 3.5mm stereo audio cables such that the speaker output from the radio connects to the microphone input of the soundcard and vice versa. Each splice was soldered and insulated with heat-shrink tubing. The entire joint between the three cables was then secured with more heat-shrink tubing. Each 3.5mm plug was marked with colored electrical tape to make it easy identify which cable plugs into which port of the soundcard (red for microphone, green for speaker).

Operation

To operate, I plug simply plug in the cables and connect the USB soundcard to my computer (a big advantage of this model of soundcard is that it does not require special drivers for Windows 10 or Linux, it is truly a plug-and-play device). When I am ready to send data I simply key the radio using the PTT switch on the side and click the transmit button in the digital software. When the transmission is finished I unkey the radio. I had originally played around with an external VOX circuit as well as the UV5R’s internal VOX feature, however, neither of them would reliably key the radio and stay keyed throughout an entire data transmission and I decided they were unnecessary. Using manual keying is actually somewhat of an advantage since it simplifies the interface, reduces complexity, and doesn’t require changing the radio’s configuration.

Calibration

I used FLDIGI to test the interface over simplex to another radio. After some experimentation I found that with the radio’s speaker volume set at a comfortable level (about 1/4 turn) a setting of 50% for the soundcard’s microphone gain was a good audio level for receiving data. For transmitting, I found that a setting of 1% from the soundcard’s speaker produced the cleanest output.

If I was going to build more of these I think I would add a 10K ohm resistor at the connection between the soundcard’s speaker output and the radio’s microphone input. This would attenuate the signal somewhat and allow for finer control over the transmit audio level. Even so, as it stands now the audio is clean and data transmission worked flawlessly. I have used this interface on my local digital net and it performs very well. This has definitely found a place in my Go Kit.

Update (March 2017)

I recently discovered that FLDIGI has a built in TX Audio Attenuator feature. Using this I can achieve much finer control over my transmit audio level, even with the soundcard’s speaker output set to 1% volume. This makes adding a resistor in the transmit audio wiring unnecessary.

Ham Radio EMCOMM Go Kit – Version 2

Last year I put together both VHF/UHF and HF go kits. While functional, neither of these was as capable or robust as I ultimately wanted my go kit to be. My new goal was to build an all-in-one station in a box that was not overly bulky or heavy.

Design

If you look around the internet you will see a lot of people building go kits in rack cases. I always liked the sturdiness and modularity of this type of case, but not the bulk. Most builders us a full size 6 unit case, which is not compact (roughly 24″ square and 13″ tall) nor lightweight (over 18lbs). After evaluating the equipment I planned to use in the kit I realized that I did not need a full depth case. Using a shallow case saves me 8″ of depth and cuts the weight as well. I laid out several possible equipment arrangements in CAD and found that if I kept the kit fairly barebones (no SWR meters or external antenna tuners, only one external speaker) I could also move from a 6 unit case to a 4 unit and still fit everything I needed. The 4 unit shallow case I used is 22.4″ x 16.2″ x 9.1″ and weighs 12.8lbs.

The general design philosophy for this project was to have all of the equipment mounted to two shelves (one on the bottom and one at the top). After my experiments in CAD I found that a good organizational layout was achieved with the power supply, power distribution, and HF transceiver mounted on the bottom. As part of the power distribution system I wanted to incorporate an automatic backup power switch. This allows the power system to seamlessly change from AC wall/generator power to battery power. While not necessary, this is a nice feature to have because it prevents your radio from turning off while operating if there is an interruption of power (which can easily happen in emergency and field operations).

This left the VHF/UHF transceiver, speaker, and two SignaLinks for the top shelf. The SignaLinks are separated by the speaker to easily differentiate which unit is connected to which radio. I went with multiple digital interfaces because while I will most likely never be transmitting on both V/U and HF simultaneously, it can be very handy to be able to monitor both at the same time or to monitor one while transmitting on the other. Having two units also allows me to never worry about changing radio and SignaLink wiring to operate on the band I need to.

In order to simplify the cabling between the SignaLinks and my laptop I decided to us a powered USB hub and to make the USB hub accessible on the back of the case. This makes it very convenient when in the field since I don’t have to reach into the case to plug in the interface cables. The addition of a rear mounting plate gave me a place to pull out the V/U transceiver’s antenna connection for easier access as well.

I decided one external speaker would be adequate based on the layout I settled on. In this layout there is a fair amount of space below the V/U radio’s speaker to allow for sufficient sound output. The HF radio, however, has much less space above its top mounted speaker. Another consideration I made was that FM audio on V/U is generally very clean, especially compared to SSB audio on HF. Based on this I chose to use the speaker with the HF radio.

Parts

Construction

The Powerwerx power supply is perfect for go kits. It is very compact (6″ x 5″ x 2″), has convenient Anderson powerpole connections on the front (in addition to terminals on the back), and can be secured with mounting brackets.

The Yaesu 450D offers a lot of bang-for-your-buck and is relatively compact and lightweight as well (9lbs). The built-in automatic antenna tuner does not have the widest range (3:1), but I don’t plan to use it with non-resonant antennas so it should be more than adequate. Making use of the internal tuner also allowed me to eliminate an external tuner from the design, which was one of the key reasons I was able to fit everything inside a 4 unit case. The 450D was mounted using 2.5″ steel brackets along with M4 machine screws and 1/8″ nylon spacers to prevent the brackets from rubbing against the radio’s enclosure. I had originally intended to use Yaesu’s mobile mount for the 450D, however, it took up too much space and would have affected my layout. This arrangement lifts the radio about 1/2″ off of the shelf which should provide plenty of ventilation.

In the preliminary layouts I had planned to use a West Mountain Radio PWRgate and Rigrunner for backup power switching and power distribution. This plan proved impractical due to space restrictions, however, I found the perfect substitution in the Low Loss PWRgate. It is about half the size of the other backup power switch and it provides 3 output powerpoles which eliminates the need for a Rigrunner or other distribution block. While the LLPG is rated for 25 amps vs the 40 amps of the other unit, this should still be adequate for my purposes. The LLPG is very lightweight and was mounted using heavy duty double stick tape.

The Kenwood V71A was mounted using it’s mobile mounting bracket. The voltage converter for the USB hub was screwed to the shelf using its mounting tabs. The other equipment on the upper shelf was mounted using either heavy duty velcro (SignaLinks, USB hub) or double stick tape (speaker). I also added some rubber strips to the bottom of the speaker because I found in test fittings that the clearance between the speaker and the HF radio was only about 1/8″ and I didn’t want any inadvertent contact between them when the case is moved.

Cable Management

Part of eliminating the Rigrunner from my build meant that I had to provide some protection for the power wiring and radios. This was done using inline fuse holders with ATC style fuses. I also had a fair amount of radio interface and USB cables to manage. The shelves I chose are vented which makes them perfect for using wire ties to secure everything in place. I also wanted to make the go kit as straightforward as possible to assemble and disassemble. Part of this goal was limiting the wire tying of cables to individual shelves. This means that if I want to remove a shelf, I only need to disconnect the handful of cables that are connected between the two shelves (two power, one speaker audio, one SignaLink), then unscrew the shelf and pull it out. No cutting of wire ties is necessary.

I really wanted to be able to stow the radio microphones inside the go kit and I found that I could velcro the V/U radio’s mic to one of the HF radio’s mounting brackets and the microphone’s cable would then fit nicely between the power supply and HF radio. This is especially convenient since the microphone jack is in a position that makes disconnecting it a bit of a pain.

The HF radio’s mic is stowed using velcro and a strap to the inside of the front case lid. The lid has enough depth that the mic can fit without contacting the front of the power supply. The power supply AC power cord is stowed using a similar strap method as the HF mic, except it is in the rear case lid.

Weight

Part of the goal of using a smaller rack case was to cut down on weight as well as bulk. I had estimated that I could build the go kit and keep the weight around 35lbs. In the end the kit weighs 40.5lbs. I think the lesson I took from this is that wire and mounting hardware add up to more weight than you might realize.

Operation

The kit is very straightforward to setup. Once the lids are off I simply unstrap the microphones and power cord. Then I can either plug in AC power or a battery, hook up my antennas, connect USB to my laptop, and I’m on the air. I am very happy with how little bulk this kit has; with the lids removed the case is only 12″ deep and easily fits on a small table. The kit is small enough to integrate perfectly into my home station, which makes it very convenient to make sure everything is fully functional for field operations. I am very pleased with how this kit turned out and I learned a lot of along the way, especially about case layout and parts fitment.

Update – Microphone Connector (February 2017)

After using my Go Kit for a few weeks I realized that the Kenwood V71’s microphone connector was not in the best location. It is on the side of the radio and when the mic is being used it twists and otherwise stresses the microphone’s connector. To improve this situation I decided to extend the radio’s mic connection to the front of the Go Kit. I accomplished this using a 1 foot ethernet patch cable and a RJ45 Inline Coupler. The coupler was mounted on the top of the power supply with heavy duty double stick tape. This new arrangement makes the microphone connection much more accessible and greatly reduces the stress on the connectors.