What Should Be My First Antenna?
To start off, the dipole is the easiest to construct, since all that is needed is two pieces of wire each 1/4 wave long, a center insulator, and either 50 or 72 ohm coax or twinlead depending on how low you want your swr to be. The impedance of a half wave dipole fed in the center is 72 ohms, but it works fine with 52 ohm coax. An inverted v dipole, where the center is higher than the ends, has an impedance that will vary around 50 ohms, depending on the heights of the ends in relation to the center and the center height above ground. A folded dipole has an impedance of 300 ohms, and can be made out of and fed with 300 ohm TV type twinlead.
The dipole is a good antenna and a lot of DX has been worked with just a dipole and low power. The pattern is a figure eight broadside to the antenna. In other words, at right angles to the direction the antenna is hung. A dipole that is running north and south has the main lobes going east and west. With this in mind, it is possible to aim your signal in a given direction. Indeed, dipoles have been made that rotate on the higher bands for just this reason. Since the dipole is bi-directional it only needs to be rotated 90 degrees. There are a lot of dipoles up in the world because they do the job.
The other popular version of the dipole is the inverted V, so-called because it looks like a V since the center is higher than the ends. The resonant frequency can be changed by raising and lowering the ends, but it is easier to just set it and forget it. The higher the center, the better it gets out, also the higher the ends are, the better it works. The inverted V tends to be more omni-directional than a regular dipole, as the pattern tends to spread out along the line that the antenna is running.
An interesting thing about the inverted V is you can alter the feed point impedance by altering the angle of the legs. However, that changes the resonant frequency of the antenna and the length of the legs has to be changed. The resonant frequency also changes if the height of the center is changed. So, all of this must be kept in mind when dealing with changes made to the antenna.
It is also a good idea to use a balun at the center of the inverted V or any dipole if you are feeding it with coax to make the transition from an unbalanced feed lint to a balanced antenna. This will pretty much stop stray rf currents from flowing down the feedline to cause TVI, and other nasty things from happening. It will also help to maintain a balanced figure 8 pattern from either the dipole or the inverted V. Of course if you are using open line or twinlead you don’t have to worry about this transition since these feed lines are balanced.
It is just as important to keep in mind that tuning of the antenna is as important as tuning up the kilowatt final. It is not too hard to get your antenna up, just time consuming. Most people use an swr bridge to resonate their antenna. BUT, there is a better instrument to do this with and that is an antenna bridge, several of which are on the market. The reason a antenna bridge is better than an swr indicator is that unless you have the swr bridge at the center of the antenna, your feedline can and will influence your readings. The way to avoid this is to have the feedline an electrical 1/2 wavelength long or a multiple thereof. The reason for this is that a 1/2 wavelength reflects the impedance of whatever is connected to the opposite end. In other words, if you put a 90 ohm deposited carbon resistor on the end of a 1/2 wavelength long coax, you will measure 90 ohms plus the rf resistance of the coax with the rf bridge. An swr bridge will show some swr. Incidentally, the rf bridge will allow you to accurately measure rf electrical lengths. It is better to have a feedline that is an electrical 1/2 wavelength than one of a different length due to the influence an odd length cable can have on your antenna tuning. It is better to coil up the extra coax and stow it somewhere. This will allow the antenna to also achieve maximum bandwidth.
At this point it would be appropriate to state that any sort of conducting object within 1/4 wavelength of the antenna is going to affect the tuning, impedance and pattern of your antenna. To be more specific, a chain link fence that runs broadside to a horizontal antenna is going to affect the tuning of the antenna a certain amount, as is a metal patio roof under the antenna. A vertical will be affected by vertical conducting objects the same way. If you are beginning to realize that everything in the immediate vicinity of an antenna can have an effect on its tuning, you are right. It is very important to get the antenna tuned up correctly for maximum efficiency, and your solid state transmitter will not shut down due to high swr. The old tube transmitters would tolerate mismatches more than the solid state rigs do, and a tube rig would spit fire and hiss and melt something, usually easily repairable if there was a severe mismatch in the antenna circuit.
The transistorized rigs shut themselves off or commit hari kiri if things are not just perfect. Either is not desirable, both result in no signal and one in great expense. So, let us continue down the road to better signals.
“I want to operate more than one band. How is that going to affect the antenna and feedline if I get my antenna tuned up on 80 meters and want to operate on 40 meters.” Well, the antenna is going to become two half waves in phase, since each 1/4 wave element on 80 is going to be somewhere in the vicinity of 66 feet long and that is equal to 1/2 wave on 40. So, the total length of the 80 meter antenna will be equal to one wave length on 40. Since the antennas are fed at the center with equal amounts of power, the currents are going to be in phase. So you will get some gain from that antenna.
As for operating a forty-meter antenna on 15 meters, that will work fine, except the feedline will not come out at 1/2 wavelength. In this case, the feedline will come closer to 1 1/2 wave length which will be just fine if you using 1/2 wavelength on 40. The element lengths will come out close to 3/4 wave length. Again, there will be some gain as this antenna will act as a broadside array for the same reasons as mentioned for the 80/40 dipole. Twenty meters with a 40 meter antenna will work fine since the lengths work out the same as the 80/40 dipoles.
The patterns of the antennas operated in this manner will be strange and many lobes will pop up in different directions as bands are changed and that sure will make life interesting. You will need an antenna tuner for sure if you choose to operate in this manner, but it works and works well and it is cheap. An 80 meter dipole, fed with a 1/2 wavelength, can be used on all harmonic bands above its primary frequency range, but you must be able to tune out the reactance which calls for an antenna coupler of some sorts. The older Johnson Matchboxes were very adept at this type of operation, and excelled at multi-banding a twinlead fed dipole or inverted V.
Another variation on the dipole consisted of two inverted V antennas with their centers at the same point and one fed 180 degrees out of phase from the other. This gives an omni-directional pattern, depending on what is surrounding your antenna, and a low angle of radiation, which is fine for DX. Keep in mind the dipole has been around a long time and will be around for as long as there is some one to use it.
The next antenna many absolutely detest is the vertical. But, the vertical has a lot going for it. It is usually unobtrusive, has a low angle of radiation and easy to put up. A vertical usually is not as good as a dipole for contacts close up due to the angle of radiation being so low. But, they can lay down a good signal at a DX location. If several are used in a phased array, you can just about switch directions nearly instantly. For the low bands 160/80/40, the use of phased vertical arrays is the only practical way to get any gain on these bands without spending a huge amount of money for towers and rotary arrays. Maintenance is easier and phased arrays don’t catch the eye or airplanes as much as a 80 meter 3 element yagi.
Vertical antennas come in several sizes that work well. First is the 1/4 wave, which is the most common found on the ham bands. Verticals of this type DO require a ground system of radials, and it would help to resonate the entire ground system with a series tuned circuit. Most hams string out as many radials as they can, not always in a straight line, but the more the merrier. A ground rod at the end of each radial is nice, but expensive.
There has been several articles written on verticals and at least two or more books on amateur vertical antennas. One fellow wrote an excellent article on maximizing radial lengths. Basically, he said that 1/8 wavelength radials had more current in the system than an equal system of 1/4 wavelength radials. So, there is room for experimentation there, if any one wants to pursue it further.
There are several types of vertical antennas that do not need a ground system and one of them is the vertical dipole. A vertical dipole is just what the name says, a dipole hung vertically. The impedance does not change and the antenna becomes omni-directional. The feedline needs to be kept at right angles to the antenna for at least 1/4-1/2 wavelength to minimize rf coupling back into the feedline. But, this is true about any antenna. It is most practical at frequencies above 20 meters due to the size of anything for the lower frequency bands. This type of vertical can be phased just like the 1/4 wave vertical and it will work just fine as a directional array.
The other non-radial vertical is the 1/2 wave vertical. This type of vertical has a very low angle of radiation, and is an excellent DX antenna. Again, the size of the antenna is limited by the frequency used. The Cushcraft R3 is an example of a 1/2 wave trap vertical and it is remote tuned for 20, 15, and 10 meters. It is only 6.7 meters (22 ft) tall and is self-supporting. A 1/2 wave vertical could be made for any band with proper loading techniques. By a combination of center and top loading, a 160 meter version could be put up. The 1/2 wave vertical does need a matching network since it is being fed at a high-impedance feed point. It does have the advantage of getting the major current node above the surrounding ground level objects, which will increase your radiated signal and cause the radiation pattern to be less distorted by the presence of objects in the immediate antenna field.
The vertical antenna does seem to be more prone to certain types of noise than a horizontal antenna and you should keep this in mind. Also, a vertical needs to have a static bleed-off rf choke at the base connected to the ground system to keep the static electricity from building up.
The single-wire antennas are the simplest ones to put up, and will do a good job, as long as you are willing to live with the shortcomings of this type antenna. This antenna needs to have a good ground and some sort of antenna matching unit. If you do not use a good ground, you will get rf all over the place and burns will be common place. So will TVI and the goodwill between your neighbors will vanish rapidly. An antenna coupler will be needed to match the varying impedance of the wire antenna to the transmitter as you change frequency. It is better to have the antenna where you can feed it with coax to an antenna coupler out of the shack and remote tune it. This will keep the rf out of the shack and off of the rig. That may not be possible, so take whatever precautions you can to keep the fire off of the rig and in the antenna.
Be sure all of your equipment is grounded together by a ground strap and then grounded by the shortest possible lead to a good rf ground. An end fed 1/2 wave antenna is being fed at a high voltage point. So, be prepared to deal with that in your shack if you just poke it into a coupler on the top of the transceiver. If you feed a 1/2 wave antenna though a coupler of some sort and use a balanced feedline of 1/4 wavelength with only one side hooked to the 1/2 wave radiator, then you have a ZEPP antenna. There will be some rf in the shack and some radiation from the feedline. It can be used as an all-band antenna, but you will get rf in the shack on some of the bands.
A 1/4 wave wire can usually work fine just plugged into a coax connector on the back of the rig, since the impedance is usually close enough to work fine without any matching network, but one would be advisable, just in case. A good ground is definitely required in any case. Keep in mind having the end of an antenna come into the shack can cause a problem due to inductive coupling into the house wiring with all of the various problems rf can cause when it gets into solid state ac powered devices. It might not be worth it to use this one unless you are operating portable somewhere, for a very short time.
The random length wire is one the antenna putter-upper person forgot to measure. This wire antenna definitely needs a coupler, as the impedance will vary drastically from band to band. Again, a good ground is definitely needed for this antenna to work against.
A counterpoise is another thing you can use with long wire and other antennas. The counterpoise is a wire or several wires, equal to but not less if you can manage it, that is mounted close to the ground, but insulated from it to increase the capacity to ground through a low impedance capacitive coupling to ground. It is not meant to replace a stations ground system, but to supplement a poor rf ground. A counterpoise also can lower the radiation angle over a poor ground of a wire antenna. It can be used with any antenna.
Now that you have had a look at the basic antennas out there, the next thing is to figure out what type of operating you want to do. Ragchew with the guys on 7.213 MHz over about a 600-800 mile radius in the daytime, chase DX on the lower end of 40 meters at night, chase the DX on 20/15/10 meters with QRP, operate traffic nets on 75 meters at night, or whatever. Only you know what you enjoy doing and the choice of the correct antenna can make the difference between enjoying your hamming and being miserable.
Keep in mind the lower you hang a wire the higher the angle of radiation and the stronger your signal will be close in on the lower bands, because the sky-wave will come down closer to where the ground wave poops out.
160 meters is in a class by itself, and antennas get rather LARGE, but it is the only true mf band we have. It is a fun band though. For the most part the vertical is not too good for close in communications unless you are on 160 since its ground wave extends further out than the other bands. Get your antenna up as high and in the clear as best you can and just see what you can work.
Remember these facts of antennas:
1. A poor antenna is better than no antenna.
2. An antenna that works well for you might not work for someone else due to many variables, some known and some not.
3. You will never know how well an antenna works until you try it.
4. Never condemn an antenna unless you fully understand why it did not work.
5. Choose an antenna appropriate for what you plan to do. A rhombic is not a good choice to work stations within a 300-mile circle of you.
6. Research your requirements as thoroughly as you can.
7. Do not put up more than you can afford to have blown down more than once a year. It WILL happen one day!
8. Make your antenna choice based on your situation and operating requirements, not someone else’s.
9. Antenna height increases as the square of the severity of the lightning storm.
10. Antenna height decreases with the rarity of the DX station and how bad you need it for DXCC.
11. Subscribe to antenneX, you need this vital information for reference.
It is important to remember there are so many variations of the antennas mentioned here. Far more than can be listed in this brief article. There is room for experimentation. There are numerous books and back issues of the ham magazines that explore many of the possibilities. After all, antennas are not too expensive unless you are into huge towers and a rotating aluminum overcast. The average ham can experiment with wire antennas forever. Just keep notes and accurate records for future reference such as photographs and a article in antenneX. Test equipment doesn’t have to be expensive. A noise bridge and a wattmeter or vswr bridge and lots of reference books will make it interesting.
Remember, antennas are the cheapest thing you can use to increase your signal strength, both on transmit and receive. If you are unable to put up a tower and beam for 20-10 meters, a phased array of some sorts could be the solution, either vertical or horizontal. Phased arrays have a lot to offer, as a vertical array can change direction as fast as the relays can switch, and there is no rotor or tower to worry about, which is nice. Horizontal arrays can be rotated, and one like the W8JK array can cover 20-10 meters if it is fed with twinlead and a tuner, with no traps. It only has two elements and is bi-directional, but it does work well and has been around for many years. There are a lot of other antennas that have been around for years and work very well. Some work better than some of the newer ones, but they were lost in the shuffle down through the years. So do your research thoroughly, and experiment! It is the way to knowledge.
Originally posted on the AntennaX Online Magazine by Richard Morrow, K5CNF
Last Updated : 16th March 2024