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 light-duty 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), there are no traps or coils, 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 insulated 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 car’s 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.

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.

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.

Ham Radio EMCOMM Go Kit – Antennas

Mast System

My first priority was to have a good VHF/UHF antenna system. A magmount on the roof of your car is OK, but for local line-of-sight communications the gain and height of your antenna are very important. I also wanted something that I could easily transport and erect by myself.

Antenna Mast (2)After some investigations I decided to aim for a simple lightweight mast system that I could mount to the trailer hitch on my car. The base for this setup is a hitch mount flagpole mount. For the mast I chose the MFJ 1904H. This mast solves a lot of potential problems for a portable mast system:  it is 5 feet long when collapsed making it easily transportable in my car, it is non conductive and will not interfere with any antennas mounted on it, and despite being made of fiberglass it is fairly sturdy (each tube wall is 1/8″ thick). I don’t intend to heavily load this mast so this should serve my needs well. In order to achieve a tight fit between the flagpole mount and the mast I used a section of 2″ PVC pipe as a spacer. When fully extended the top of the mast is about 21 feet high.

I also purchased a 33 foot version of this mast design from Max-Gain Systems. While this version requires some guying, the additional antenna height can greatly increase performance.

VHF/UHF

Antenna Mast (3)Antenna Mast (1)For the VHF/UHF antenna I chose the Two Way Electronix Dual Band Slim Jim. As someone who uses a J-Pole antenna as my base VHF antenna, I am very familiar with how well these antennas perform. The Slim Jim is a J-Pole made from 450 Ohm ladder line so that it can be rolled up for easy storage and transport. I mount the antenna to the mast using a nylon bolt and wingnut the passes through the insulation at the top of the antenna and a hole drilled in the top fiberglass section. This setup is very light weight and has virtually no wind loading which makes guying the mast unnecessary (under average wind conditions).

HF

For HF I did considerable research regarding what type of antenna is appropriate for emergency communications. A lot of ham radio is focused on making contacts at great distances (DX). This necessitates a low angle of radiation from the antennas being used. For a dipole this means that the antenna should be at least a half wavelength above ground. The most common HF bands used for EMCOMM are 40 & 80 meters (one half wavelength on 40 meters is about 66 feet, 132 feet for 80 meters). For EMCOMM purposes, however, we generally only need to communicate within a couple hundred mile radius of our location. This requires a Near Vertical Incident Skywave (NVIS) propagation path. It turns out that this makes our lives a lot easier since a dipole can be used for NVIS when it is mounted much lower than it would typically be. Instead of trying to get a dipole very high, mounting it at 15 to 20 feet is ideal for this application. Another benefit of this approach is that at this height the dipole loses almost all of its directionality and is essentially omnidirectional.

HF Antenna #1 – Loaded Dipole

My 80/40 Loaded Dipole was built specifically to be center supported by my 21 foot fiberglass mast. It is lightweight, only 76.5 feet long (59% of a typical 80 meter dipole), and resonant on both bands.

HF Antenna #2 – End Fed Half-Wave

Similar to the Loaded Dipole, my 80/40 End Fed Half-Wave antenna is resonant on the two most common EMCOMM bands. It is also only 76 feet long (58% of a typical 80 meter dipole) and is quick and easy to deploy in the field as a sloper when a single strong support is available.

HF Antenna #3 – Folded Skeleton Sleeve Dipole

Field Setup (1)Field Setup (2)When space and strong antenna supports are available my 75/40 meter Folded Skeleton Sleeve Dipole makes for an excellent EMCOMM antenna. It is resonant on both bands and is only 107 feet long (81% of a typical 80 meter dipole) making it somewhat more space efficient without reducing performance through the use of loading coils like my Loaded Dipole and End Fed Half-Wave.

HF Antenna #4 – Hamstick Dipoles

Antenna Mast (4)In an effort to maximize portability and reduce both setup time and the footprint of my antenna system I bought 80 and 40 meter versions of MFJ’s hamstick dipoles (MFJ-2240, MFJ-2275). These are heavily loaded antennas that use a base section consisting of a coil wound on a fiberglass rod with a stainless steel whip on the top. While a small loaded antenna will not have the efficiency or the bandwidth of a full size antenna, it is considerably smaller (15 foot span). The dipoles are lightweight and my fiberglass mast seems plenty strong enough to support them.

Performance (updated February 2017)

I have done 24 hour WSPR tests of both the Loaded Dipole and End Fed Half-Wave antennas and they perform similarly, which is to say they are quite effective antennas. I 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.

To test the Folded Skeleton Sleeve Dipole my Ham Radio club used it during Field Day 2016 and made over 350 contacts. They even loaded it up on bands other than 80 and 40 meters and it performed well. I would say this is definitely the best antenna of the four, however, it is also the largest and heaviest.

I have yet to do much with the Hamstick Dipoles, but I plan to do some testing in the future.

Folded Skeleton Sleeve Antennas

Skeleton Sleeve Dipoles (4)I am always interested in trying different antenna designs, especially if they are simple to construct and provide increased functionality. While perusing some old issues of QST magazine online I found a series of articles that discuss a design called the Folded Skeleton Sleeve. The design is a unique way to build a dual-band resonant dipole or groundplane vertical. The articles appear in the May 2011, October 2011, October 2012, December 2013, and March 2015 issues of QST magazine.

I was particularly interested in this antenna design because a simple resonant dual-band antenna could be very useful for deployment at Field Day or for EMCOMM purposes. Other multi-band antenna designs exist and can perform quite well (windoms, off-center-fed dipoles, G5RVs, non resonant end feds, dipoles fed with window line, etc.), however, most of these require a wide range antenna tuner to achieve a decent SWR on multiple bands. Other designs, such as trap dipoles, can be heavy and cumbersome with multiple points of failure. The folded skeleton sleeve design exhibits non of these limitations.

Design

Folded Skeleton Sleeve AntennaThe folded skeleton sleeve at first looks like a standard folded dipole, however, the top radiator is not continuous. Two notches are cut along the top of the window line to create the parasitic element that allows for operation on the higher frequency band.

A 75M / 40M antenna should be perfect for both EMCOMM (these are the most common HF bands used for emergency communications) and Field Day. A 40M / 20M antenna is equally perfect for Field Day and the combination of the two provides a lot of operating versatility from two simple antennas that cover the three busiest Field Day bands. I also decided to construct a 40M / 30M antenna for use as a portable antenna for digital communications.

Construction

Skeleton Sleeve Dipoles (2)Skeleton Sleeve Dipoles (3)I built the antennas using 18AWG stranded copper-weld 450 Ohm window line (Wireman #553) and folded dipole insulator kits (Wireman #804) which make fantastic strain reliefs for securing the window line. I also made my own 1:1 baluns in a similar design to what I have done before, except this time I used FT-150A-K toroids and 18AWG wire which allowed me to make the baluns smaller in size while still being adequate to handle 100W. To house the baluns I used Bud Industries PN-1322-DGMB NEMA 4X enclosures. These are well made boxes and they feature convenient mounting tabs that are easily bolted to the center insulator.

75/40 Bandwidth

75 Meter Band

  • 2:1 SWR:  3.68-3.785
  • 3:1 SWR:  3.63-3.86

40 Meter Band

  • 2:1 SWR:  7.18-7.238
  • 3:1 SWR:  7.1-7.3

While the bandwidth of this antenna is not particularly wide, it is easily matched to the radio’s 50 ohm output with practically any antenna tuner.

My ham radio club used the 75/40 at our Field Day site for the duration of the event. While obviously intended for use on 75 & 40 meters, the antenna was used on the higher bands as well with the help of a wide range antenna tuner. Over the course of field day this setup resulted in over 350 CW contacts.

40/30 Bandwidth

40 Meter Band

  • 2:1 SWR:  7.158-7.33
  • 3:1 SWR:  7.073-7.448

30 Meter Band

  • 2:1 SWR:  9.93-10.24

This antenna exhibits better bandwidth than the 75/40 and even reaches an SWR of 1.1:1 on 30 meters.

40/20 Bandwidth

This antenna is by far the best design of the bunch. This configuration results in an SWR of under 2:1 across the entirety of both the 40 and 20 meter bands.

Antenna Winders

Skeleton Sleeve Dipoles (5)Since ladder line can be annoying to work with since it doesn’t coil easily, I decided to build some winders from 1/2 inch PVC pipe to keep the finished antennas organized. I built a larger one for the 75/40 antenna and smaller ones for the 40/20 and 40/30 antennas. I am really pleased with how these turned out and plan to build more for use with other antennas; they are a fantastic way to avoid a tangled mess.

 

6 Meter Quad Turnstile Antenna

6M Quad Turnstile (2)After my less than successful attempts on 6 meters with my collinear array, I decided to try another design that I had been looking at for some time. A quad turnstile consists of two cubical quad loops oriented in a diamond configuration and angled 90 degrees apart from one another with both diamonds sharing the same top and bottom points. The advantage of this design over a single quad loop is that when phased 1/4 wavelength (90 degrees) apart the combination of the two antennas creates an omnidirectional radiation pattern. This type of antenna can also be made from two crossed dipoles, however, using full wave loops instead of half wave dipoles provides about 1 dB additional gain at low elevation angles (there is a great article about building a 6 meter quad turnstile written by L. B. Cebik, W4RNL in the May 2002 QST magazine that goes into further detail about the performance and advantages of this antenna design).

Another advantage, from a construction perspective, is that the spreaders required for a dipole turnstile would have to be 10 feet across. The spreaders for quads only need to be 7 feet across meaning that the use of lightweight pvc is that much more practical. The quad configuration is also perfect for being suspended by a push up fiberglass mast since the antenna is very light weight and virtually all of the loads are directed vertically down the center of the antenna which is also the center of the mast. This results in very little flexing and stress on the light duty fiberglass section at the top of the mast. I built my antenna using the Max Gain Systems MK-6-Standard fiberglass mast which stands 32 feet tall when fully extended.

From previous experiments with 6 meter loops I have found that 20 feet of insulated 14 AWG wire is resonant at the bottom of the 6 meter band (just above 50 MHz) where the SSB activity is concentrated.

6M Quad Turnstile (5)6M Quad Turnstile (6)The feed point is the most complex component in the entire antenna. It consists of a piece of 1/4″ thick Lexan with three SO-239 connectors (one for the feedline and one for each end of the phasing line) and four #10-32 stainless bolts (one for each loop end) mounted to it. The SO-239s and bolts are then wired together such that the feedline is wired directly to one loop and one end of the phasing line and the other end of the phasing line feeds the second loop. I used red and yellow electrical tape to mark which bolts attach to which loop. I also notched the Lexan sheet to fit around the mast so that I could wire tie it in place.

6M Quad Turnstile (7)6M Quad Turnstile (8)The phasing line is made using RG-63 coax which has an impedance of 125 Ohms. This is required because the feedpoint impedance of each of the loops is also about 125 Ohms. When fed together via the phasing line the final antenna impedance is approximately 62 Ohms which matches well with the standard 50 Ohm feedline (for this antenna I used a run of 100 feet of LMR400 coax). I purchased my RG-63 coax from The Wireman. The phasing line needs to be 1/4 wavelength long at the bottom of the 6 meter band. To calculate this you can use the formula (246/frequency) = quarter wavelength in feet. Therefore 246/50.5 = 4.871 feet = 58.46 inches. Next we take into account the velocity factor of the RG-63 coax, in this case 84%. Therefore 58.46*0.84 = 49.1 inches which is the length that the phasing light should be including the connectors on each end.

6M Quad Turnstile (11)6M Quad Turnstile (10)The PVC spreaders are made using 3/4″ PVC conduit glued into a 4-way junction box. By drilling a 3/4″ hole in the center of the junction box it allows the spreader assembly to slide down the top mast section and rest on top of the 1″ section of the mast. This is left to float in place and is not attached to the mast in any other way.

6M Quad Turnstile (9)The key to the construction of my version of a quad turnstile is that the entire antenna hangs from the top of the mast. To accomplish this I used a 1/2″ PVC cross with a nylon bolt running through the center. The bolt slides in the end of the 3/4″ fiberglass mast section and prevents the PVC cross from sliding off the top of the mast. I then fed the antenna wires through the cross such that the wires intersect at 90 degree angles. This method serves to secure the wires to the peak of the mast as 6M Quad Turnstile (12)well as providing some strain relief for the antenna wires. I then splayed out the wires and ran them through notches cut at the end of the PVC spreaders. I then centered the wires relative to the top of the mast and taped the wires to the end of the spreaders to keep them in place until they are attached to the feed point. The wires were then attached to the feedpoint using ring terminals that were soldered to the ends of the wires. The ring terminals make it easy to connect the wires to the bolts mounted on the feedpoint.

6M Quad Turnstile (3)6M Quad Turnstile (1)To erect the antenna I first raised the top 3/4″ section of the mast until the top wires became taught. This only requires about 3 feet of the top section to be extended such that the spreader assembly is not lifted off of the lower mast section. I then locked the top mast section in place. Next I raised the 1″ section of mast until the lower wires were taught and secured the feedpoint in place with a wire tie and taped the feed line and phasing line to the mast for strain relief. Then I continued raising each mast section until the mast was completely raised, resulting in a peak height of nearly 30 feet. I then finished guying the mast. For this antenna I only guyed the mast at 3 intervals, the bottom, the middle, and the top since the antenna is not heavy and is very evenly loaded on the mast. Three guy lines per 6M Quad Turnstile (4)interval were used made from UV resistant rope anchored using 10″ spiral ground anchors. This resulted in a very stable mast and the antenna that has held up well, even on breezy days. A tautline hitch is a great knot to know for tensioning guy ropes for masts as well as tents when camping.

After erecting the antenna I checked the SWR and found it to be 1:1 at the bottom of the 6 meter band. I also found that the 2:1 SWR bandwidth was quite large and easily covered the SSB portion of the band. I also noticed that a nearby 6 meter beacon station that was typically an S3 on my collinear array was now an S7 on my quad turnstile, which is a huge improvement.

The following day after getting the antenna on the air there was sporadic E band opening in North America and I was able to hear several stations. During this opening I worked my first 6 meter contacts, receiving good reports from stations in Oklahoma, Arkansas, Alabama, Tennessee, and Manitoba. Not too bad for 100W into an omnidirectional antenna in western Pennsylvania.

I also worked about four hours of the June 2016 ARRL VHF Contest and made 20 contacts with stations in 14 grid squares. Like a lot of antenna systems, this one allowed me to contact most of the stations that I was able to hear. I have, however, gained an appreciation for why most people use directional antennas for VHF work. While the extra gain directional antennas provide would definitely be a positive, I can see now how favoring one direction over another can be especially advantageous on 6 meters. More than once I could hear multiple strong stations on the same frequency and with a directional antenna I could have significantly nulled out one of those stations in order to make it easier to hear and work one station at a time. Another advantage would be the ability to focus your signal in the direction in which the band is open, instead of broadcasting in all directions.

With all of that said I am very pleased with how this antenna project worked out. This design is an inexpensive and effective way to get on 6 meters and make contacts which was my goal in the first place. It is also a good all around lesson in antenna design, construction, and phasing lines.

Slim Jim Antennas

2 Meter Slimjim (2)2 Meter Slimjim (1)I am a big fan of the J-Pole antenna style and have built a few of them in the past (see here and here). Electrically the J-Pole is a half wavelength antenna that is end-fed by a quarter wavelength stub to achieve a feed point impedance of 50 Ohms. The Slim Jim is very similar except that there are two half wavelength segments with the second folded next to the first. This arrangement makes them ideal to be constructed from 450 Ohm ladder line. This also allows them to be incredibly compact and portable since they can be rolled up very easily.

2 Meter Slimjim (4)2 Meter Slimjim (3)I found a very useful calculator that gives you all of the dimensions needed to build a Slim Jim or a J-Pole from ladder line (you will have to convert from metric to imperial units yourself). Using this calculator set for 146 MHz (the middle of the 2 meter band), I assumed my 450 Ohm ladder line had a velocity factor of 0.91 and cut it to a length of 56 inches (not including the 0.5 inch on each end to be stripped and soldered together). I then cut the half wave radiator 36.75 inches from the top and the quarter wave matching section 18.375 inches from the bottom. This left a gap of 0.8 inches between the two. The 50 Ohm feed point was calculated to be about 1.8 inches from the bottom, however, using my antenna analyzer I found the the feed point should be 2.1875 inches from the bottom. With a piece of RG-8X feedline soldered at the feed point this antenna has an SWR under 2:1 across the entire 2 meter band. To complete the antenna I drilled a 0.25 inch hole at the top so that the antenna can more easily be hung from a mast or a tree or clipped to a wall if used as an indoor antenna.

This type of antenna is a very economical way to build a VHF or UHF antenna. It also has a considerable amount of gain compared to a standard quarter wavelength vertical and is just as easy to build and transport.

Baluns & Ununs

Anyone building antennas will come across designs that either recommend or require the use of a balun or unun. The design and construction of these components can get quite complex and are beyond the scope of this blog and my own knowledge. In short these devices act as impedance transformers from balanced loads to unbalanced loads (balun) or from unbalanced loads to unbalanced loads (unun). They can also be used as a common mode choke to eliminate any RF on a coax feed line’s shield. That said, it is actually quite easy to construct your own baluns and ununs and to learn something in the process. You can also save a considerable amount of money.

1-1 Balun (2)1-1 Balun (1)Amidon sells a good starter kit for building baluns and ununs. It includes everything you need including a book with dozens of designs with various impedance transforming characteristics. 1-1 Balun (6)1-1 Balun (3)I used this kit to make a 1:1 balun. Since the kit uses 14AWG wire, it should be capable of handling 2KW of power continuously. This is overkill for me since I will never be putting more than 100W through the balun. The 1:1 balun is essentially a choke that blocks current flow on the shield of the coax feed line. It is constructed using 10 bifilar wraps on the toroid core using approximately 4 feet of wire.

For other projects I decided to use the same FT-240-K core with 18AWG wire covered in 16AWG PTFE insulation. While the 18AWG has less power handling capability, it should be more than adequate for 100W usage as well as being cheaper and easier to work with.

4-1 Balun (2)4-1 Balun (1)The first balun I made using these materials was a 4:1 current balun. This balun is intended to transform a 200 Ohm load for use with a 50 Ohm coax feed line. This type of balun is commonly used in 4-1 Balun (3)Off-Center-Fed dipole antennas because the feed-point is placed at the location on the antenna where the impedance is approximately 200 Ohms on multiple bands. I intend to use this balun as part of a 6 meter collinear antenna that I am building. The balun is constructed using two sets of 8 bifilar wraps on the toroid using approximately 8 feet of wire. Each pair of windings is then wired in series with the other pair. This design can be thought of as two 1:1 baluns wired in series and in fact an alternate design of this balun uses two separate 1:1 balun cores wired in series to achieve the same affect.

9-1 Unun (2)9-1 Unun (1)Next I made a 9:1 unun for use with an end-fed antenna I am building. End-fed antennas exhibit very large impedances and consequently require considerable impedance transformation to 9-1 Unun (3)get the feed point within the range of an antenna tuner. Unlike a dipole, an end-fed antenna is unbalanced and therefore an unun is used instead of a balun. This design uses 8 trifilar wraps on the toroid using approximately 6 feet of wire. Each wrap is then wired in series to create the desired impedance transformation.

1-1 Line Isolator (2)1-1 Line Isolator (1)I also made another 1:1 balun. The main difference here is that I constructed it using two SO-239 connectors because I intend it to act as a coaxial feed line isolator. My plan is to use this in conjunction 1-1 Line Isolator (3)1-1 Line Isolator (4)with the 9:1 unun as part of my end-fed antenna project. The idea here is that a section of coax from the 9:1 unun acts as the counterpoise for the end-fed antenna and the line isolator is used to choke the RF current in the shield of the coax and allow the remainder of the feed line to continue to the antenna tuner without risk of radiating RF.

For all of these projects you can see that I used colored electrical tape to mark the various windings. This is essential to keeping track of the wiring and assuring that the windings are wired together correctly. For all of these I also used standard NEMA 4X 4″x4″x2″ plastic electrical boxes which are cheap and commonly available. I also used 10-32 stainless steel hardware for the antenna connections and silver-teflon SO-239 connectors.