Loop Skywire Antenna & Remote Tuner

Now that I’ve had this antenna setup for a few years now I have come to recognize the drawbacks. The biggest of these is a lack of tuning bandwidth. This resulted in having to retune the system even when changing frequency by only a few kilohertz, very annoying. After playing with a MFJ 926B remote automatic antenna tuner at Field Day this year I decided to modify my antenna to make use of one of these units and see if it improved my operation. The 926B is actually pretty similar in design to my LDG tuner except it is mounted in an enclosure suitable for use outside and can be powered via coaxial cable using a BiasTee power injector so no extra cables are needed. It automatically initiates tuning when a mismatch over 2:1 SWR is detected while transmitting and it saves the match settings to memory.

The idea of a remote antenna tuner is that it allows the tuner to be located at the feed point of the antenna. This means that the tuner is matching the impedance mismatch of the antenna only; not the antenna, plus feedline combination that it was dealing with previously. This allows the tuner to find a match much more easily and also results in a much better tuned bandwith because the only variable changing is the impedance of the antenna not the impedance of the antenna and feedline combined.

A side benefit of this new setup is that in order to reach the tuner as it is mounted on the side of my house I had to add some wire to my antenna which now contains approximately 270 feet of wire. The antenna is now solidly resonant in the 80 meter band. In addition to adding wire I separated the feed point in the air by about 10 feet. This allows the wires to drop to the tuner at an angle in order to keep the shape of the loop as intact as possible and prevents the two ends from contacting or crossing one another. I also installed an Alpha Delta TT3G50 surge protector in the coax line from the tuner.

In the short time that I’ve had this setup on the air I have been very pleased with its operation. To tune the system I switch to CW mode on my Icom 7200 and transmit a tone (with the power turned down to 10W). The tuner then initiates its tuning cycle and matches the antenna. This generally only takes 2-3 seconds, much faster than before. It also tends to find much better matches and regularly achieves close to 1:1 SWR. As hoped, the tuning bandwidth is greatly improved as well and I am no longer required to retune every time I move around a band. This new setup is also much cleaner looking on the house with no ladder line or balun, just wires going to the low profile tuner and a coax run along the brick.

Loop Skywire Antenna – Update

After reevaluating the trees in my yard I realized that I could rework the layout of my loop skywire antenna. This would allow me increase the size of the loop, improve the feed point arrangement, and increase the height of the antenna.

After adding a fifth anchor point the loop is now a distorted pentagon instead of trapezoidal in shape (see the sketch for the rough layouts). The new arrangement is not only larger, but also higher than before, which should help its performance. With a new circumference of approximately 244 feet of wire the loop is much closer to resonance on the 80 meter band than it was previously.

Due to the repositioning of the feed point I had to shorten the feedline. I decided on 37 feet of 300 Ohm ladder line as an acceptable non-resonant length for the feedline. This is a good length since it keeps it well off the ground while still providing some slack for movement. So far the performance has been at least as good as the previous version.

Loop Skywire Antenna

Design

When I bought my house this spring, I immediately started planning an HF antenna for my ham radio station. It’s been several years since I last had a permanent base station set up and I wanted to get on the air. After evaluating my options, I decided that a loop antenna would be my best option. The biggest advantage for me is that a large loop antenna fed with ladder line allows for good performance on a wide range of frequencies using a single antenna. This design also allows me to maximize the amount of antenna that I can fit on my 1/2 acre lot (an 80 meter loop is only 72ft on a side vs the 135ft overall length of an 80 meter dipole) without having to put up masts or towers.

The general idea of a loop skywire is to put up as much wire as possible, without worrying about cutting it to resonance, and feed it with ladder line. Since ladder line exhibits very low loss compared to coaxial cable, even with a large impedance mismatch, the total amount of signal loss in the ladder line will be minimal. With a good antenna tuner between the ladder line and the radio, all of the HF ham bands should be available.

Components

For wire I purchased Wireman #531, which is insulated wire made up of stranded 13 AWG copper-clad steel. The steel core makes it strong (400 lb breaking strength) and helps minimize stretch, while the copper cladding gives it good electrical conductivity. The insulation helps to protect the wire from the weather.

The feedline I chose is 300 ohm ladder line, which is a little harder to find than its 450 ohm cousin. Some ladder line is cheaply made, but this type from DX Engineering uses 18 AWG copper-clad steel and works very well. They also make a great antenna feed point kit with built in strain relief slots for use with their 300 ohm ladder line. It is well worth the money.

While I could have used a balanced tuner, or some other type of manual antenna tuner, I decided to go with an automatic antenna tuner for my station due to their ease of use and their ability to store impedance matches to memory. The memories allow the tuner to pull up previous tuning settings without having to rematch the radio to the antenna, saving a lot of time. I use a LDG AT-200ProII in my station and it has worked great so far with my loop antenna. I chose this model for its wide impedance matching range, its ability to store 4000 frequency & impedance combinations, and its 200 Watt power rating. Although I don’t plan on using more than 100 Watts in my station, the 200 Watt model is only slightly more expensive and because of its higher power rating it will hopefully be even better equipped to withstand the high impedance mismatches that this antenna presents.

The final piece of this arrangement is the balun. In this case I used a high power current balun between the ladder line and the antenna tuner. This device blocks the current on one side of the ladder line from continuing on to the shield of the coax on the other side. In this way it transforms the balanced load of the antenna and feedline into an unbalanced load for use with the antenna tuner and radio. I could have made my own balun, but I decided to buy a DX Engineering BAL050-H10-AT. This is heavy-duty (rated for 10KW) balun designed for exactly this type of application and is much better constructed than anything I could have made on my own.

Construction

Putting up the loop was a relatively straightforward process. The first step was to pick which trees to put the support ropes in. I don’t have a ton of options on my small lot, but four trees were spaced appropriately for me to make a trapezoidal shaped loop. To get the ropes (I used 3/16″ Dacron) into the trees I used some light nylon cord tied to a wrench and tossed the wrench over the highest branch I could reach. I then pulled the heavier rope up over the branch. Next I attached the insulators that I had made using 1 inch 45 degree PVC elbows (painted black for stealth) and bungie cords. The bungies act as a stress relief between the trees and the antenna, thereby allowing the trees to move in the wind without jerking the antenna too hard. I used bungies on three of the four corners, leaving only the corner nearest the feed point without one.

I then ran the antenna wire through the insulators until I had both ends at the location of the feed point. By taking the slack out of the ropes I was able to start trimming the antenna wire such that when the insulators were lifted as high as I could get them the antenna wire was tight. After a few adjustments, and some branch trimming, I was able to get the antenna in the air. I then set the antenna back down and attached the ladder line to the feed point and raised the antenna to its final position.

Finally I mounted the balun to the side of the house and ran the ladder line to the balun. To support the ladder line I attached some rope to the feedline with zip ties and hoisted it using an eyebolt screwed into the eave of the house. I also made a spacer/strain relief for the ladder line to keep it away from the aluminum siding on my house. This is necessary because if ladder line is too close to anything conductive it can unbalance the feedline, thereby causing it to radiate like the antenna.

Performance

After trimming, my loop ended up being 215 feet in circumference and uses 47 feet of ladder line. I lucked out on the length of ladder line that I needed; you have to be careful not to use a length that is harmonically resonant on any of the frequencies you wish to operate, otherwise the feedline could radiate and cause interference. While this antenna is technically a little short for use on the 80 meter band, it will tune on that band along with all of the remaining HF ham bands (except 160 meters).

Considering the limitations of my property in terms of the size and height (around 30 feet) of the antenna, I couldn’t be happier with it so far. I love the ability to operate from 3.5 to 30 MHz without having to switch antennas. Overall performance has been great. In my limited time using my new station I have been able to contact stations in Europe and throughout the US, as well as have a lot of fun in the Pennsylvania QSO Party (my home state) where I was able to contact pretty much every station that I could hear.

2 Meter J-Pole Antenna v2

2+Meter+J-Pole+Dimensions2+Meter+J-PoleI recently purchased a house and decided to build another J-Pole for use as the 2 Meter antenna for my new station. My old one is still mounted on my parent’s house and in good shape after several years of exposure to the elements. My old design’s performance was fairly good, but for this new build I decided to tweak the dimensions somewhat (with the help of my MFJ-259B Antenna Analyzer) to get the SWR as low as possible across the whole 2 Meter band. By adjusting the feed point and lengthening the driven element I was able to get the following results:

2+Meter+J-Pole+FeedpointFrequency      SWR
144MHz          1.8
145MHz          1.6
146MHz          1.4
147MHz          1.3
148MHz          1.5

J-PoleI really like the design of this antenna due to its simple and cheap construction, ideal feedpoint placement for low stress on the coax, and the fact that the whole antenna can be easily grounded since at DC it is essentially a short circuit.

Carolina Windom Antenna

 

WindomI have wanted to build a multi-band wire antenna for some time now and this past Field Day I had an opportunity to use a very good one. The Carolina Windom is essentially an off-center fed dipole (OCFD) that uses a portion of its feed line as a vertical radiator. I used one to make about a 100 PSK31 contacts on 20, 40, and 80 meters during Field Day.

The key to an OCFD’s operation is the fact that there is a point on the antenna where the input impedance is approximately 200 Ohms at multiple frequencies. When fed with a 4:1 balun this provides a reasonable match to the standard 50 Ohm load that my coaxial cable and radio like to see. Even if the antenna doesn’t provide a perfect 1:1 SWR over all bands, it keeps it low enough that a simple antenna tuner can compensate for any mismatch. The problem with OCFDs is that since the two legs of the antenna are of different lengths, the currents in each leg are out of phase. This means that in order to avoid feed line radiation, you should use a 4:1 current balun to compensate for this current imbalance. These are not readily available for sale, but can be constructed from kits. Here’s a great article which describes how to wind your own current balun using this kit from Amidon. You can also buy an equivalent balun from DX Engineering or Balun Designs.

The Carolina Windom, however, wants the feed line to radiate (at least a portion of it) in order to gain the vertical radiation and some performance. To achieve this the Windom uses a 4:1 voltage balun, which matches the antenna’s leg voltages and then uses a separate 1:1 choke balun to isolate the feed line from the vertical radiator. Both of these baluns are readily available and relatively inexpensive.

The first step in constructing my Carolina Windom was to cut the antenna wire to length for an 80 meter version. I used these measurements from Radioworks, who sell pre-assembled Windoms, but other sites also show measurements and formulas for cutting a Windom for any band. My Windom has the same 133ft overall length of a traditional dipole, but is divided into 50ft and 83ft legs instead of equal lengths. Since this antenna will be used for temporary setups such as Field Day and the PA QSO Party, I didn’t make it out of heavy duty wire, instead I used insulated #14 stranded copper wire. This wire is a good compromise between strength and weight. Construction of the Windom is very straightforward; simply solder one end of each wire to opposite sides of the 4:1 balun and attach insulators to the other ends. For the 4:1 voltage balun I used the W2AU 4:1 and for the 1:1 choke balun I used the W2DU inline-HF, both of which are available from Unadilla. These are well constructed commercial baluns that work well for these purposes. In the picture I do not have the choke balun connected since I did not have it at the time, so in its place I created a poor man’s choke balun by coiling about 10 turns of my RG-58 feed line.

In order to test the antenna I set up my new fiberglass mast to about 25 feet with the Windom on top. While this isn’t an ideal height, it was fine for a test. I connected the feed line to my radio and tested the SWR. I was able to get a match using my Icom IC-703’s internal tuner on all of the HF bands. Since the 703’s internal tuner can only deal with SWRs of less than 3:1, this means the antenna is performing as expected, providing a decent match to the radio on all the HF bands. For a further test I tuned around the 20 meter band. Hearing a special event station in Maine, I gave him a call and he came right back to me. Not a bad first test, getting into Maine with 10 watts. This is exactly what I was hoping for, a solid performing multi-band antenna that I can use for temporary operations. Wire antennas are very simple and cheap to build, and this one is a great project for any type of station.

Windom2Here’s a picture of my finished antenna rolled up for storage. In between the 4:1 balun and the Unadilla W2DU inline-HF 1:1 choke balun is 22 feet of RG-8X coax that functions as the vertical radiating section. You could use any type of 50 Ohm coax, but I had some laying around from other projects and it is a good compromise between size/weight and signal loss for a portable antenna such as this.

20 meter Groundplane

groundplane1Most hams are familiar with the quarter wavelength ground-plane antenna design. It is often the first antenna they buy or build for use on 2 meters after receiving their technician license. It is a design that performs well and exhibits low input impedance, making it ideal for use with ham equipment without the need for special matching techniques. The antenna is easy to construct and due to this simplicity is also highly economical. When considering the type of antenna to build for field day to use with my PSK31 setup this design was the obvious choice. It provides both low take-off angle and omni-directional radiation, allowing me to maximize my operating capability from a simple station. The antenna is made up of a single pole which supports the radiating vertical element and is guyed in place with nylon rope. The two radial elements are spread out and held in place by ropes.

groundplane2The base of the support pole is made of a ten foot piece of 1.25 inch schedule 40 PVC pipe that was cut in half for easier transport in my car. It is joined in the center by a 1.25 inch PVC coupler. Mounted on top of the PVC pipe is a 13 foot extendable fiberglass fishing rod which I purchased at Gander Mountain (I had originally planned on using a 16 foot rod but none were available when I went to the store, with additional height the radials can be lowered at a steeper angle which in turn raises the input impedance closer to the desired 50 ohms). I joined the fishing rod to the pipe by first removing some of the plastic at the base of the fishing rod so that it could slip inside the pipe. Next I drilled a single hole through the pipe and rod so that I could secure the two pieces together using a small bolt and nut to prevent the rod from sliding further into the pipe. I also wrapped the fishing rod with some electrical tape to compensate for the difference in diameter of the rod itself and its plastic base (this allows the rod to fit snugly inside the PVC pipe thereby stiffening the rod and pipe connection).

groundplane3groundplane4The radiating element and both radials are 16.5 foot long 14 AWG insulated stranded copper wire. For ease of assembly I soldered the radiating element to the center of a SO-239 connector and attached solder lugs to the radials. This allows me to attach the radials to the SO-239 with two small bolts passed through the holes on the connector, simplifying construction in the field. I taped the radiating element to the pole prior to raising the antenna. The radials were attached after the antenna was erected and securely guyed since the feed point is only 5 feet off the ground providing easy access for mounting. From start to finish assembling the antenna and guying it in place took about 30 minutes to do by myself (with more people it could easily be erected in 5-10 minutes).

The performance of this antenna was better than expected. It matched perfectly on the lower end of 20 meters despite being cut for the center of the band (this is due to my use of insulated wire which adds capacitive loading to the antenna, electrically lengthening it). Whether you are looking for a solid performing base antenna or a light, compact, portable antenna this may be the project for you.

2 Meter J-Pole Antenna

jpoleThis is perhaps the cheapest gain antenna for 2 meters that can be built. Total cost for this antenna is under $10 (excluding coax) and it can be built in about an hour. Using what is called “Plumber’s Delight” construction I soldered all joints using a propane torch, lead-free/non acid core solder, and some soldering flux. While there are several iterations of the J-Pole that can be built, I liked this one because it does not require the builder to directly solder the coax to the copper pipe. Instead, a SO-239 is soldered to the T connector and a short piece of wire (I used insulated #12 stranded copper) is soldered to the center conductor to feed the driven element. My version of this antenna is mounted on my chimney and works very well, providing 2:1 or better SWR on the entire 2 meter band. It is incredibly strong and I have experienced no problems with wind or other weather.