Many BVRC club members have Technician licenses and can operate on 10 Meters. 10 Meters is the best band when the solar cycle favors us and the worst HF band when it does not. Fortunately we still have a couple of years during this cycle when it is easy to work stations all over the world on 10 Meters.
Although it would not be possible to detail all the possible antennas you can easily make in a short article, I will give you details on a few antennas you might consider. Because I dislike antenna tuners or high-ratio transformers for transmitting, I won’t cover any antennas that require them. The goal should be an antenna with an SWR of less than 2:1 at the back of the rig.
First, a Few General Notes
The larger the conductor the shorter the antenna will be compared to one with a smaller diameter. If the wire has insulation the length will also be shorter as compared to using bare wire. It is not significant and does not matter too much in terms of length but you should be aware of it. The thing about a wire antenna is that it is easy to adjust it to resonance by making it longer or shorter.
It is a good idea to create a choke at the antenna’s feed point using a 2.4-inch #31 mix ferrite core with several turns of coax wound through it. This will help prevent common-mode current on the coax shield. For this purpose, wind about 8-10 turns of small diameter coax through the core and that will suffice. The Mouser part number for that core is 623-2631803802. Everyone should have a few of those handy, as they are useful when dealing with RF interference.
Building antennas is fun and does not cost you much. I have not purchased a commercially made antenna for use at any of the stations I have had in about 50 years.
In general, the higher the antenna is, the better it works. However, a simple antenna at a half wavelength off the ground will surprise you — that is about 18 feet for 10M. I believe that in a contest it would be possible to work 75 different countries in one weekend with 100 watts and a dipole at 15-20 feet on 10 Meters, given good conditions.
An antenna with gain in one or two directions radiates less in the other directions. You cannot achieve gain with an omni-directional antenna like a single quarter wave vertical. In fact without a good radial system a vertical will have negative gain. If a vertical is all you can install, that is better than nothing — but a simple dipole at a reasonable height will outperform a vertical by a significant margin. Verticals are great for lower frequency bands like 160 and 80 meters. Consider that an 80M dipole would have to be flat and up about 135 feet to equal a 10M dipole at 17 feet.
Flat Dipole
It is hard to beat a flat dipole on any band. Consider that the gain from the Yagi on the tower at ALETA is between about 5 and 7 dB over a dipole. For reference, an S unit is about 5 dB. If you had two of those Yagi antennas in phase with a tower twice as tall you would get approximately 3 dB more. The elevation angle with the highest gain would be lowered, which is good for DX. The point, however, is that hams go to great lengths and expense to have something better than a simple dipole, and it is not easy to beat one by a significant margin.
A dipole is 75 ohms at resonance. This means that the best SWR you will achieve with a flat dipole fed with 50-ohm coax will be about 1.5:1. If you like to look at an SWR meter with nearly zero reflected power, there are tricks to match 75 ohms to 50 ohms.
One of those tricks is the 12th wave transformer. You use an electrical 1/12th wavelength of 50-ohm coax feeding the 75-ohm antenna at the feed point, then an electrical 1/12th wavelength of 75-ohm coax connected to that. You will then see 50 ohms at the end of the 75-ohm section and can run 50-ohm coax from that point to the radio. If you used RG-6 at the feed point with a velocity factor of 82%, that length for 28.4 MHz would be 28.4 inches — a handy coincidence.
Those numbers are scalable for any band. For example, a 15-foot length of 50-ohm coax with a velocity factor of 66% connected to a 75-ohm 40M antenna, followed by another 15-foot length of 75-ohm coax with the same velocity factor, will transform your 75-ohm antenna to 50 ohms — a perfect match from antenna to radio. Note that the coax coiled through the ferrite choke counts as part of the 12th-wave portion.
To make a half-wavelength dipole, use two 8’3″ lengths of #16 insulated wire (or 8’4-1/2″ of bare #16), joined at the center with an insulator. The center conductor of the coax goes to one wire; the shield goes to the other. Make the wires a little long to start so you can trim to resonance.
Find two tall trees, string about 20 feet of wire between them with small-diameter rope or nylon twine, and you are on the air. A half-wavelength flat dipole at a half-wavelength above ground (15-20 feet) has about 7.5 dB more gain than a good vertical — roughly the difference between 100 watts and 550 watts!
For end insulators, a short piece of small-diameter PVC with one hole for the wire and another for the rope works fine. If you are unsure whether a piece of plastic is a good insulator, put a cup of water in the microwave and set the insulator next to it (not in the water). A good insulator will still be room temperature after 30 seconds on high.
Vertical Antenna
Many questions come up about verticals. A 10-meter vertical is easy to make — 246/Freq(MHz) gets you in the ballpark. A piece of PVC in the yard with a wire taped to it will work. But remember: verticals make terrible antennas without a decent radial system. The best you can hope for without one is an omni-directional antenna with zero gain instead of negative gain.
If your radials will be on the ground, use as many as possible. I have friends with 160-meter verticals using 140 ground radials. I would not consider a vertical for 10M unless I was prepared to install about 40 radials — the longer the better. Ground-mounted radials are not resonant, so length is not critical. Elevated radials with an elevated feedpoint (a ground plane antenna) will outperform a ground-mounted vertical because there is less loss with elevated radials. The radial length only affects vertical resonance when the radials are elevated.
A quarter-wave vertical may not hold its own against a dipole on 10M unless the dipole is only 12 feet off the ground and/or the vertical has an excellent radial system.
Half Square — An Interesting Antenna to Try
The half square is two approximate 1/4-wavelength vertical wires connected at the top by a horizontal half-wavelength wire. Fed at a top corner with the coax running away from the antenna (rather than hanging down by the vertical element), it achieves a nearly perfect 50-ohm match. Each vertical wire is 104 inches, and the horizontal section is 205 inches. Maximum radiation is broadside and perpendicular to the horizontal wire.
Put this between two trees with the bottom wires 10 feet off the ground and you will have a very effective antenna. All it takes are two trees about 20 feet tall and 20 feet apart, and about 33 feet of wire total.
If you can feed the center of the horizontal element you can double it and add another vertical, making what is called a Bobtail Curtain — that gives you another 2 dB over the half square.
Yagi
Now we are talking about something that will beat a dipole every time. A Yagi is a horizontal antenna with a driven element similar to a dipole, plus additional parasitic elements. The coax connects only to the driven element; the lengths of the other elements determine whether they act as a reflector or director. A three-element Yagi has a reflector, a driven element, and a director. You can build a wire Yagi that works as well as a rotating aluminum-tube model.
With just a 12-foot boom and three elements you can achieve about 5 dB over a dipole. If you would like to build a simple 3 or 4 element Yagi for 10M, I can give you dimensions for whatever materials you have available. Element spacing and especially element length are critical — these antennas are typically designed with specialized software. It would not surprise me to learn that I have spent several thousand hours with that software over the last 40 years.
To summarize the progression: a single vertical has zero gain even with a good ground system. A ground plane eliminates the need for an extensive radial system to get gain from negative to zero. A half square provides several dB of gain over a single vertical; a Bobtail Curtain adds another 2 dB. But nothing beats a flat dipole as high as possible between two trees — unless you build a Yagi or a Rhombic. If you have about ten acres and four supports available, call me. You could be king of the band with a rhombic antenna!
Coax
RG-6 — the kind cable TV companies use, available at Home Depot or Lowe’s — is your friend if you are on a budget, do not have a long coax run, and are not using an amplifier. It is cheap and will easily handle 100 watts, though you will lose about 1 dB per hundred feet. I would use it even for a 100-foot run if budget demanded it.
RG-6 is 75-ohm coax but easy to transform for a single band. Connectors can be installed in under 30 seconds with an inexpensive tool, and adapters from the F connector to a PL-259 are readily available. If you have a 75-ohm antenna like a dipole, it is a perfect match and you can put the 1/12th-wave transformer at the transceiver inside. If the antenna is 50 ohms, transform it to 75 ohms at the antenna feedpoint and back to 50 ohms at the radio.
For buried runs, I recommend Commscope RG-6 made for direct burial. I once had a sloping 40M dipole — top at about 50 feet, sloping down to near ground — with a 12th-wave transformer and a perfect match. It handled 1500 watts without complaint. I would not run 1500 watts on RG-6 on any band higher than 40M, however.
Everyone’s situation differs based on location, available trees, and ability to install an outdoor antenna. An inexpensive solution exists for every problem that would otherwise keep you off the air. Antennas behave differently in different environments, so experiment — you will have fun and also avoid paying retail price for a commercial antenna that may not even work in your yard.
73… Stan, K5GO
