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.

Update – Integration with New Power Box (November 2017)

Part of building my new Power Box involved modifying the power circuitry for my go kit. Because the battery switching components are now off board I no longer needed the Low Loss PWRgate. In its place I installed a Powerwerx PD-4 distribution block. I also used a powerpole mounting clamp and a piece of ABS plastic to create a mount for the output of my power supply. This gives me two solid points of connection from which I can wire to my power box. Or if I am running exclusively off of the power supply I can use a simple jumper for self contained operation.

QRP Go Kit

After assembling a solid set of QRP gear this year I wanted to put everything into an easy to transport package. To house and protect the kit I used a Monoprice 13″ x 12″ x 6″ Weatherproof Hard Case. This case is the perfect size to fit my mcHF transceiver, and Elecraft T1 autotuner, along with a 3″ external speaker, hand microphone, and power cable. All together the case and equipment weigh a little under 7.5lbs.

With this kit, all I need is 12VDC power and an antenna and I am on-the-air. This should pair perfectly with a small battery and either my random wire or end fed half wave antennas that I built recently.

Update (March 2017)

After completing my mcHF’s new case I decided to update my QRP go kit accordingly. Since the new case has an internal speaker I was able to eliminate the external speaker from the kit. In its place I put a 6Ah Lithium-Iron-Phosphate battery. This should give me between 6 and 12 hours of runtime at 5 Watts output, depending on how much I transmit and what mode I am using. While more expensive than sealed lead acid batteries, LiFEPO4 batteries are lighter in weight, smaller in size, provide more usable amp-hours, and last many more charge-recharge cycles. This 6Ah model weighs about 1.75lbs, compared to 5lbs for a 7Ah sealed lead acid that actually provides less usable power. This iteration of the kit weighs a little under 9lbs, over 3lbs less than the previous version (including the lead acid battery) and it is more compact as well.

mcHF Update – Serial EEPROM, New Tuning Knob

While checking some of the posts on the mcHF Yahoo Group, I came across one from Andreas that emphasized the importance of installing the optional EEPROM. If the EEPROM is not installed the radio saves settings to the CPU’s FLASH memory whenever the radio is turned off. All of this memory writing adds up and can lead to failure of the FLASH memory. Since I don’t want to worry about replacing the CPU in the future I ordered the recommended EEPROM (24LC1026) chip and installed it on the UI board. I also installed the required 0.1uF capacitor using the smallest through-hole component I could find. Upon booting up the transceiver the EEPROM was detected by the firmware and the radio seems to be working perfectly. This was an easy and worthwhile upgrade, especially since the EEPROM only costs about $3.50 and should protect the FLASH memory from being worn out in the future.

After some extensive searching I finally found the perfect tuning knob for the mcHF. OKW makes a very nice line of knobs, part of which is a series designed for communications gear. To match my mcHF’s black enclosure I bought the A3140069 which is 40mm in diameter and mounts to the encoder’s 6mm shaft using a compression collet. This knob can take two different styles of cover (with or without finger dimple) in an assortment of colors. I went with the A3240109 cover which features a finger dimple for faster tuning. This is a huge upgrade over the tuning knob provided with my case and really improves both the looks and functionality of the mcHF. Not bad for under $5.

HF Random Wire Antennas

Resonant antennas have a lot of advantages: they are efficient, impedance matched to your transmitter and require minimal tuning. The main disadvantage of resonant antennas is that they are nearly always only usable over a single frequency band. Non-resonant antennas do not present a match on any band by default, however, they can be easily matched to a wide range of frequencies. One of the most common ways to match a transmitter to a non-resonant antenna is to use a 9:1 UnUn combined with an antenna tuner.

100W Random Wire

I built this version for field use and wanted to make the design as flexible as possible. To this end I built the antenna such that I can easily lengthen it when extra room is available. The default length is 53 feet and the antenna can be extended to 124.5 feet. These lengths were chosen because they are not resonant on any ham band. The 9:1 UnUn for this antenna uses a FT240-K ferrite toroid wound with 18AWG enamel wire. The UnUn is mounted to a DX Engineering Balun Bracket to provide a mounting point and antenna wire strain relief. The antenna extension was made by using two DX Engineering Wire End Insulators that are be bolted together for strain relief and Anderson Powerpoles for the electrical connection of the 14AWG antenna wire. For a counterpoise I made two 50 foot lengths using 24AWG speaker wire. I can also use the shield of the feedline coax and then isolate the antenna from the transmitter using a 1:1 Balun/Choke. I have used this antenna using only the 53 foot section of wire and was able to tune all of HF and made a few contacts using my HF Go Kit, although some bands required adjustment of the counterpoise length in order to be in range of the Yaesu FT-450’s antenna tuner.

QRP Random Wire

After experiencing some success with my high power version I decided to build a QRP version. The QRP 9:1 UnUn uses a FT140-43 ferrite toroid and is wound using 24AWG enamel wire. This combination should easily handle 10 watts. The physical construction of the UnUn itself uses the same strain relief technique as my End Fed Half Wave Matchbox, where 1/8″ acrylic is epoxied to the enclosure used to house the toroid. For this antenna I used 26AWG stranded copperweld and cut it to 29.5 feet with an additional extension to 53 feet. This should allow for quick and easy field deployment using my 31 foot lightweight fiberglass mast. I did some experiments with my QRP transceiver and my QRP Autotuner and was able to tune all of HF using this configuration and two 50 foot counterpoises.

Overall I think these random wire antennas are a good addition to my antenna arsenal. They are not necessarily the best option, however, they are very versatile and can prove useful when a simple multi-band antenna is required.

End Fed Half-Wave Antennas

Half wave dipole antennas are generally considered the reference point for all antennas in ham radio, especially on HF. When fed from the center, a dipole makes for an easy impedance match to 50 ohm coax. When fed off-center at an appropriate location (typically the 1/3 point) and fed with a 4:1 balun, the dipole becomes a solid multi-band antenna. Feeding a half wave antenna from the end, however, presents additional challenges because the impedance is in the thousands of ohms. In spite of this, end feeding antennas can be an incredibly convenient configuration because you only need one support (like a tree) and you can easily place your operating position at or very near to the feedpoint of the antenna. This has led to this antenna design to being very popular with portable operators and others who want an antenna that is easy to erect quickly.

QRP Matchbox

While researching this type of antenna I found a couple of blogs (here and here) that have a lot of good information regarding end fed half wave antenna designs. These designs rely on the principles used by the PAR Endfedz which consist of an impedance transformer between the antenna and transmitter as well as a capacitor across the feedpoint. Based on this design I made an impedance transformer using a FT140-43 ferrite toroid (this size toroid is overkill for a QRP application) with 27 turns on the secondary and 3 turns on the primary (24AWG enamel wire). This is then wired such that the start of both the secondary and primary are connected to the coax connection shield. The other side of the primary is connected to the coax center pin. The remaining secondary connection is the attachment point for the antenna. A 150pF is then wired across the coaxial connection. I used a 1000V mica capacitor since very high voltages are present at the feedpoint.

The matchbox was constructed using a 3.25″ x 2.125″ x 1.5″ ABS plastic box and 8-32 stainless steel hardware. To provide strain relief I epoxied a piece of 1/8″ acrylic to the back of the matchbox enclosure. I also made a strain loop at the end of the antenna wire for attachment to the acrylic sheet using an S hook. This allows the acrylic to carry the load of the antenna, not the antenna connection point. I also used pieces of acrylic for the end insulators since it is the perfect material to weave small wire through and lock it in place.

I wanted to experiment with the effectiveness of this matchbox with different antenna designs. I also wanted to test the antennas in a typical field installation configuration; in this case they were erected as a sloper with one end in a tree about 25 feet in the air and the feedpoint about 5 feet off the ground.

40/20 Meter Half-Wave

This antenna is a full size 40 meter half-wave with a tuning stub in the center to adjust the resonance of the antenna as a 20 meter full-wave. The tuning of this antenna was very straightforward; I simply tuned the main element for the center of the 40 meter band and then adjusted the 20 meter stub for the center of the 20 meter band. With the 26AWG stranded copperweld wire that I used the antenna ended up being about 62 feet long with a 2 foot long stub in the center. This antenna exhibits great bandwidth and easily covered both bands with under 2:1 SWR.

40/30 Meter Loaded Half-Wave

This antenna is a full size 30 meter half-wave with a loading coil/choke and tuning stub at the end of the antenna to provide resonance on 40 meters as well. The loading coil/choke consists of 55 turns of 24AWG enamel wire on a piece of 3/4″ PVC pipe. This coil is approximately 47uH of inductance, which should have an impedance of almost 3000 Ohms at 10MHz. The purpose of the coil is to choke off the current flow and electrically shorten the antenna on the 30 meter band while providing the necessary inductance to resonate the full antenna on the 40 meter band since it is shorter than a full half-wave on that band.

Tuning this antenna required a fair amount of trial and error because the 30 meter element and tuning stub length interact and affect the resonance on both bands. I initially trimmed the main element without the loading coil and had a good match with 42.5 feet of wire. After attaching the loading coil and several feet of tuning stub I found that the antenna appeared to be too short for 30 meter resonance and too long for 40 meter resonance. Eventually after several trimmings I found that a stub length of about 3 feet resulted in the 30 and 40 meter resonances tracking each other when I adjusted the length of the main element. I then added wire to the main element until I achieved a good match on both bands, in this case a main element of 48 feet works well. 30 meters is a narrow band and this antenna easily covers the entire band with under 2:1 SWR. Because of the loading coil, this antenna does not exhibit particularly high bandwidth on 40 meters, however, the purpose of this antenna is for QRP digital operation which does not involve a lot of tuning around, so it was trimmed to provide the best match at the low end of 40 meters and should have plenty of bandwidth for PSK and JT65 operation.

100W Matchbox

After my successful experiments with the QRP matchbox I wanted to build a more robust version for higher power applications. This requires the use of thicker gauge wire and a larger toroid to handle the higher currents and and more powerful magnetic fields. In this case I used 18AWG enamel wire wound on a FT240-43 ferrite toroid, which should easily handle 100 watts of power. A 27:3 turns ratio was used again as well as the same 150pF 1000V mica capacitor. I mounted the completed toroid in a 4″ x 4″ x 2″ NEMA 4X box and mounted it to a DX Engineering Balun Bracket. For the antenna connection I used 10-32 stainless steel hardware.

80/40 Meter Loaded Half-Wave

This antenna is constructed similarly to the 40/30 meter version described above. This time, however, the loading coil consists of 67 turns of 20AWG enamel wire on a piece of 1″ PVC pipe. This coil has an inductance of about 66uH which is required to achieve an appropriate amount of current choking at 7MHz. For strain relief I used 1/4″ Lexan sheet to make the connection points for the antenna and coil wires. I then epoxied the Lexan to the PVC coil form and bolted the connections using 10-32 stainless steel hardware. The coil was sealed using two coats of polyurethane.

I found this antenna to be easier to tune than the 40/30 meter version. This is most likely due to the larger difference in frequency ratio between the 80 and 40 meter bands vs the 40 and 30 meter bands. After trimming I found that a main element length of about 67 feet gave a good match across the 40 meter band. As anticipated this antenna has a limited 2:1 SWR bandwidth on the 80 meter band (about 90KHz). I decided to construct a way around this by adding a tuning stub to the end of the 80 meter section to allow for adjustment of which portion of 80 meters I wanted to operate in. Since the primary usage of this antenna would be for field deployment and emergency communications I would most likely need to be able to use it in the digital portion of the band (3.583MHz or so) as well as the higher end of the band (3.983-3.99MHz) where the ACS nets in my area take place. After some experimentation I found that the antenna was resonant in the voice section I wanted with an 80 meter stub 9 feet in length. I then made an additional 3 foot length of wire that I can add to the end using Anderson Powerpoles that shifts the resonance of the antenna to the digital portion of the band. This allows me to easily change the section of the 80 meter band I want to use by simply adding or removing this small section of wire. This additional wire has a very minimal effect on the 40 meter resonance of the antenna (around 10KHz) and does not prevent the antenna from achieving an SWR of under 2:1 across the entire band whether it is installed or not.

To assess the end fed’s performance I did a side by side comparison with my 80 meter loop skywire. I setup the end fed as a sloper with the loaded end supported by a tree about 25 feet in the air and the feedpoint about 3 feet off the ground. I then observed the signal strength when listening to the local ACS net on 80 meters. I found that I could copy everyone easily with the end fed half-wave, however, they were generally 1 or 2 S-units weaker than with my loop. I also used the End Fed Half-Wave during Winter Field Day and was able to easily make contacts on both 40 and 80 meters using both SSB and PSK31. With the winder this antenna weighs 4lbs, not bad considering the weight and bulk added by the matchbox. Overall I think this antenna is a very solid semi-compromise antenna for field use and will definitely be part of my Go Kit going forward.

Elecraft T1 QRP Autotuner Kit

img_0841In the months since I completed my mcHF SDR transceiver kit, I have thought about building a QRP antenna tuner to go along with it. After some investigating I came across the Elecraft T1 which is available assembled or as a kit and can handle 10W of continuous power. While I have never owned any Elecraft gear, they have a very good reputation and several people in my ham radio club swear by their equipment. The kit looked like a fun project and a perfect match for my QRP gear so I decided to order one.

img_0842The kit took about a 4.5 hours to complete. The included instructions are very detailed and do a good job of emphasizing critical parts of the build. The biggest issues arise in regard to several components that need to be mounted in a very specific way in order for the case to fit properly. The circuit boards are fairly tightly packed, but anyone with good soldering experience should have no problem assembling this kit.

img_0844img_0843The finished product is very compact and incredibly simple to operate. I really appreciate that the instructions are printed on the front label in case you forget. So far I have used it to tune a couple different antennas of various designs and it performs very well. It finds matches quickly and the relays aren’t annoyingly loud like some autotuners. I look forward to getting a lot of use out of this and my mcHF.