EF-180BV 80/75 mtr Linear Loaded Vertical
Advanced Installation and Tuning
The EF-180BV linear loaded vertical is a proven, efficient design. It has been used to set various North American and World records and will provide excellent performance when properly installed and tuned. These advanced instructions have been written after setting up and using this vertical:
Note: for in-depth information on the 6Y2A operation, complete with lots of photos and details, click here:
A vertical antenna can be of several types. In all cases, the description ("vertical") means the antenna is vertically polarized: the primary, desired energy emitted from the antenna is vertically polarized, not horizontal, nor circular. This is a common selection for the HF spectrum, as it provides a low angle take-off angle without having to raise the antenna high above ground, as with a horizontally polarized antenna. In the latter case, the take-off angle is directly related to the height above ground of the horizontal antenna. For example, a horizontal dipole at one wavelength high will have a lobe centered at about 13 degrees above the horizon. It will have a second lobe at about 40 degrees. On 10 mtrs, this height is only 35’ above ground; however, for 80/75 mtrs, this represents about 260’, a tough order without the assistance of a hill under the tower. As the old saying says, there is no free lunch. The trade-off on using the vertical is that there is no ground reflection gain, as found with the horizontal antenna. This reflection gain will add 3-6dB to the far field energy from the horizontal antenna, which is a substantial amount, so a horizontal gets "better" when it is placed above ground. A vertical antenna does not.
A vertical antenna is affected by the ground, but not in as positive a manner as the horizontal. The ground (except for salt water) will cause some of the energy to be "lost" below a certain angle, usually referred to as the "Pseudo Brewster Angle." This is about 12 degrees, but depends on the quality of the ground. Better ground will have less affect and salt water will provide an incredible ground, enabling a vertical to be one of the most impressive antennas ever used. The vertical will also lose energy in the ground, depending upon the quality of the ground. Salt water represents the absolute best case and makes a vertical a tremendous antenna, because the ground has no loss and the lobe goes down to almost zero and up to about 30 degrees. As the quality of ground is decreases, the loss increases and the low angle energy (below the Pseudo Brewster angle) is greatly reduced. Over average ground, the lobe will be centered at about 20-22 degrees. This is equivalent to a horizontal antenna at about ¾ wavelength high, which is about 200’ on 80/75 mtrs, thereby making an efficient vertical an effective antenna, even over ground. The key is efficiency, which is controlled by the antenna itself, the current return (radials) and the ground. The first two can be controlled by good design. The third, ground, is usually out of our control, except for a DXpedition where we carefully select the location!
The efficiency of the EF-180BV is excellent. It is a linear loaded design, which has the highest Q of all techniques for loading shortened antennas and tuning is straightforward. The overall height is 34’, about 60% of full size. With its high Q, the 3dB (half-power) bandwidth is narrower than full size. This is an advantage that might not be obvious. Even a full size vertical cannot cover both phone and CW segments, so having a narrower bandwidth is not too critical. The electrical advantage of an efficient, high Q, narrow band antenna is that it acts like a preselector for the receiver, reducing the noise.
The radials are the current return for the vertical. One radial can be used; however, the horizontal energy it produces is not canceled. This is the reason for a second radial going in the opposite direction. The currents on the opposing radials are 180 degrees out of phase, thereby canceling the horizontal component. The vertical portion is the primary radiator. It is tuned by adjustment of the loading system. The feedpoint impedance of a ¼ wavelength (full size) vertical with an efficient radial system is in the low 30 ohm range. The EF-180BV feedpoint will be in "high teen" range (16-19 ohms). This is stepped up to 50 ohms using a hairpin match in the form of a four turn, 3" diameter coil across the feedpoint. The spacing between turns on the hairpin is adjusted for a 1:1 VSWR.
There are many schools of thought about radials. Some are accurate, others are more mythology than fact. One of the mythological ideas is to simply lay a radial or two on the ground if you are installing a vertical on the beach. Actual testing of this idea in Jamaica shows startling results. A full size 20 mtr vertical with two radials laying on the ground was used. The ground was actually a combination of coral and volcanic rock called, "iron shore." This beach front looks like coral, with holes of varying sizes and is treacherous to walk on. It is also covered with salt water and much of the ground under the radials was salt water. With two ¼ wave (full length) radials laying on this "ideal" ground, the measured resonant frequency of the 14 MHz vertical was 11 MHz. The resonance was shifted downwards a full 3MHz by the ground, which most would think was the best possible. To correct the current return (radial) system, the radials were raised about 18" and the lengths adjusted slightly, at which point the resonance of the vertical was exactly as planned. The most efficient radial system is one that is elevated above ground. After performing careful tests, elevating an 80/75 mtr radial eight (8) feet above the ground is an effective height. A short summary:
The above has addressed using only two (2) radials. There can be installations where four (4) is needed to bring the feedpoint down to the correct range. When the feedpoint is higher than expected, it is an indication of loss. This is most likely in the radial system, which can be either too close to the ground, or the wire too small. A good idea to have in mind is to "peak" the VSWR (before matching it)! In this case, a lower feedpoint is better, as it means there is less loss. With the EF-180BV, if the hairpin needs to be fully compressed (closest spacing) for the lowest VSWR and it is still not 1:1. There is loss in the radial system. The antenna can be successfully matched by adding a turn or two to the hairpin; however, the system will not be as good as it could be. Given some difficult installations, it might not be possible to reduce the loss any further and a larger hairpin will be needed.
Actual height above ground of the vertical is another consideration. The above table for elevated radials is for the base of the vertical located near the ground. Does it make much difference whether the vertical itself is elevated? The main advantage of elevating a ¼ vertical (i.e. EF-180BV) is that the feedpoint is physically higher. What does this mean? If the vertical is a vertical dipole (1/2 wavelength), the vertical is placed so the bottom of the vertical clears the ground by some small amount (e.g. a few inches), so it is not touching the ground. This causes the feedpoint (center) of the ½ wavelength vertical to be about ¼ wavelength above ground. The result is that the feedpoint impedance is raised and the main lobe is compressed in vertical height, creating an increase of about 1dB gain over a ¼ wavelength vertical. Since we know that energy is not created, the gain increase comes from the compression of the main lobe. If the vertical can be elevated (up to a ¼ wavelength), there will be an improvement in gain. Computer models show that raising the feedpoint should be kept at ¼ wavelength or less to ensure the main lobe remains intact. If the vertical is raised higher (including a vertical dipole), a high angle lobe will be generated that will have more energy than the lower, desired lobe. This high angle lobe is not diminished until the vertical is raised much higher (more than a wavelength).
There are some cautions regarding all antennas. Most everyone is aware of the high current in an antenna, as this is a common subject when discussing losses. At the center of a dipole (or vertical dipole), the current is maximum at the center and minimum at the ends. Where there is current, there is also voltage. The voltage in a dipole is minimum at the center and highest at the ends. A vertical dipole has highest voltage at the top and bottom (the ends). A ¼ vertical has the highest voltage at the top of the vertical radiator and at the ends of the radials. This creates an installation condition what needs to be handled carefully. If the vertical is guyed (a good idea in heavy weather areas), care needs to be taken at the attachment points because of the voltages on the vertical, itself. How high are these voltages? Several thousand volts – high enough to ignite dry wood, or burn almost anything! This is why a simple dipole must use some type of insulation at the ends AND, the dipole must not touch anything along the way. A well-installed vertical (i.e. EF-180BV) uses two (2) elevated ¼ radials. The radials are connected together at the antenna, making the two radials a dipole. This is why the ends of radials are so "hot" and must be insulated from everything.
EF-180BV’s are most often used as single verticals and 4-squares. They can be used in other configurations. The World Record setting installation 6Y2A used them as 2 element parasitic vertical beams. This beam uses a driver and reflector and is described later, including setting up a 2X2 and tuning for a 4-square.
Force 12 EF-180BV
High Performance 80/75 mtr Linear Loaded Vertical
Installation Notes
I. Each installation will share common aspects, but will probably have something unique, as well. Very few locations are identical. The EF-180BV can be used as a single vertical, two or more to make a parasitic vertical beam, two or more in phased arrays, or combination of parasitic and phased.
II. The first decision is the mounting of the EF-180BV. If it is safe from traffic, it can be mounted on the stock (2’) base. If traffic from children, adults, or animals is a concern, then it should be elevated high enough for safety. Force 12, Inc. can supply any base necessary. The company has built a wide variety of bases (e.g. straight posts, tripods and hinged plates), so please use our experience.
III. The location needs consideration for the radials. As described earlier, a good installation uses two ¼ wavelength elevated radials. If one radial is used, it can resonate the antenna, but there will be horizontally polarized energy from it. To cancel the horizontally polarized energy from the single radial, a second is required. The two radials should run in opposite directions. This takes up a fair amount of space. The old thought that verticals do not take up much space must have been aimed at vertical dipoles! If the radials cannot run in opposite directions, make the best effort to have at least part of them in opposite directions. Make them as straight as possible, for as long as possible. The currents in the two radials will be 180 degrees out of phase and will cancel, leaving the vertical portion as the primary radiator.
IV. Elevating the radials can be done in several ways. One way is to have the entire vertical elevated, in which case the radials are already elevated at the beginning. It is a simple task to keep them elevated. If the vertical is not elevated, there is a simple technique to elevate the radials.
The 1997 A.R.R.L. DX Contest found our team in Jamaica setting up for a two transmitter CW operation. This was our first experience at this location and we set up verticals, because we were right next to the ocean. The problem was, however, that none of the low band verticals would match. The entire team asked me what was wrong and I spent a somewhat sleepless night figuring it out and working on a solution. Going against the answer was the "training" about laying radials on the ground when at the ocean. I decided this had to be wrong, that the radials were coupling into the ground, which was still lossy. This loss is additive to the feedpoint and made the impedance higher than 50 ohms. The radials needed to be elevated, but how to do it was not simple, as we had limited supplies. I recalled an I.E.E.E. paper earlier in the year about using elevated radials to recover performance on AM broadcast antennas that has disintegrating buried radials. One of the suggested remedies was to raise the radials at an abrupt angle to get them as high as possible, as quickly as possible. We used a technique that has since been dubbed the "buzzard wing", after all the turkey buzzards that frequented our location. By the way, they kept us working faster and remembering to keep moving! The technique is to attach a line and insulator to the vertical and pass the radial up and through the insulator. This raises the radials right away and allows it to remain high and efficient.
The following photo shows the basic technique. In this example, the radials are coming up at quite a steep angle and it is about at steep as one should use. Even with this quick rise in the radials, they perform well, and the antenna is effective: not only working "typical DX", but also European stations on 75 mtr long path. This particular EF-180BV is one of several that were installed in various locations to verify installation recommendations. This one represents a very basic, simple approach:
Photo at right: Force 12 EF-180BV, High Performance 80/75 mtr Linear Loaded Vertical
Ground mounted using only fiberglass base insulator. The red radial wires should not be installed this steep (done for the photo). They should be installed at about a 45 degree angle.
V. One item that is optional is where the radials are connected. The radials can be connected either at the feedpoint screw going through the base, or they can be "floated" and connected to a feedpoint screw passing through the fiberglass insulator between the base and the antenna. We have run verticals both ways and have found no discernable difference; however, we have not been able to use them over all types of ground. If it is not an increased degree of difficulty, using an additional machine screw through the fiberglass might be the safest decision.
VI. It is recommended that the radials be tuned. There are schools of thought regarding radial length. This mostly stems from the idea that radial length is critical and that longer or shorter ones are "better." Without replaying a lot of writing over the past year or so, our recommendation is that the radials are set close to the resonant frequency of the antenna. They can be cut to an initial length, which is best made slightly long. The reason for making them slightly longer than expected is simply that it is easier to shorten radials than it is to lengthen them.
Tuning radials is quite simple. Dean Straw, N6BV (A.R.R.L. Technical Staff) demonstrated this in Jamaica when we were setting up the 6Y2A antennas in November of 1998. Initially install the radials as you expect them to be when finished. The total length two radials can be estimated by using the formula for the length of a dipole above ground, 468/f(MHz). For a 4-square, where the antenna is set at 3.660 MHz, the radial length will initially be 468/3.660 = 128’, so each radial is half of this, or 64’. Make the initial length a little long, such as 66’. It is always easier to shorten a radial, than to make it longer.
Connect a measuring device (such as handheld units like the Autek, MFJ or AEA) to the radials as you would a regular dipole. This means connecting the leads of a 1:1 balun to the radials and connecting the balun through a short length of coax to the meter. Tune the meter for the lowest dip, regardless of frequency and regardless of what the dip is (e.g. 1.5:1, 2:1, 3:1). The dip is the key, as it is the present frequency of the radials. If you do not have such a device, your transceiver can be used as the measuring device.
Connect your transceiver to the coax feeding the balun, which is connected to the two radials. Turn off the automatic tuner in the transceiver and be sure there is no other tuner in the circuit. Reduce the power to a small amount and set for CW mode. Switch the meter to read VSWR and put on a constant carrier. Tune across the 80/75 mtr band, watching the meter for a dip in VSWR. Just like using a handheld meter, the frequency of the dip is the frequency at which the radials are presently tuned.
The radials can be adjusted for the proper frequency (i.e. 3.660 MHz for a 4-square on 75 mtrs). The VSWR at the dip will vary depending upon the height of the radials above the ground. It can range from almost 1:1 to 3:1. The radials can be set exactly on frequency, although the absolute bottom of the dip might be difficult to determine. The dip is quite broad, because the radials are actually a full size dipole. At 6Y2A, the radials were left slightly long, by perhaps 15-25 kHz.
VII. Be sure to insulate the ends of the radials! If we could have taken night photos in Jamaica, we could have shared at least two fascinating spectacles. One was the end of a 20 mtr radial that had been secured to a piece of drift wood set vertically in the coral to elevate the radial. All the radials had insulators, except for this one (not intentional). The operating house was perhaps 300’ from this antenna and while operating that evening, the end of the radial ignited the wood support. This ignition was actually more like an old style fireworks Roman candle, as it lit up the beach and we could see it easily from the house! A second incident was when the incoming heavy surf took down a radial support on one of the 80 mtr reflector elements. The end of the radial was lying on the coral/volcanic shoreline, in the salt water. Two of us went out to see what had happened, because the 80 mtr array was interfering with other bands. It was easy to spot the problem. As the 80 mtr station was keyed, two sections of the radial lit up the beach. One section was about 5’ long, coming from the base to the elevating insulator, a gap of about 2’, then another section about 8’ long after the insulator. These sections of the radial lit up like the filament in a light bulb. If we were not pressed for time because of the contest going on, we would have called some of the other operators to take a look. The support for the radial was reset and everything returned to normal. One more incident that should be mentioned here as a caution for the high voltages present on radials is the first time we set up the many verticals at 6Y4A in early 1997 for the A.R.R.L. DX contest.
Placing many antennas is always difficult, as there are guys, radials, feedlines and the antennas themselves to watch out for when you walk around. We had identified a safe walkway through the lawn area using large stones. One evening during the week before the contest we were checking out the antennas, which is always a good thing to do, especially in a windy location. As we were walking, I reminded the fellow walking with me to use the safe walkway, which was particularly important because of the radials on the 40 mtr verticals that were crossing the lawn. He knew about it, but thought it was not that important, so he was not on the path. We stopped to briefly discuss it and, as we were talking, he asked, "What’s burning?" It was his shorts, which were touching an elevated 40 mtr radial! The radial had burned into his shorts in the short time we had stopped to chat about the safe path. After that, he stayed on the path. (Quick learner!!)
EF-180BV
INSTALLATION RECAP
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