HF Antenna Installation Hints

This article is for those who are new (and not so new) to HF and need good HF wire antenna installation information, for best performance and lowest SWR across the HF bands.

Problem Solvers for Wire Antenna Installations

Of the many questions we get concerning HF wire dipoles and slopers, many deal with the same common issues of antenna installations and performance problems. Indeed, many of the problems turn out not to be problems at all when we are provided with additional information about the situation, SWR "runs" across each band and the installation "site" itself. Additional information from the customer provides useful clues in helping to solve the problems.

The questions we get seem to follow a fairly consistent pattern from those new (and not so new) to HF. Proper installation and operation of VHF/UHF antennas can beVERY different from proper HF antenna installation and that's where the "rub" can come in for those new to HF.

Due to the wavelengths of the VHF/UHF bands, coupling to surrounding objects is usually minimized by placing these antennas only a few feet or so from things in theclose-in environment (roof tops, attics, gutters, other antenna, etc.). Now, here's where things greatly change when installing HF wire antennas.

The wavelengths of the HF bands are MUCH longer than those of the VHF/UHF bands, and coupling (and therefore antenna de-tuning) to surrounding objects can and does occur when HF antennas are placed close to surrounding objects that would not have affected VHF/UHF antennas. As an example, consider a 40 meter dipole (about 66 ft. Long) installed close to aluminum gutters (40-80 ft. long) along the side of your house and you'll see what we mean. Or consider this same dipole placed close to a roof top and within a few feet of attic wiring and HVAC ducting which can be "part" of the wavelength on HF. Installation SITE factors, therefore, are where most of the problems seem to lie with HF antennas, compared to VHF/UHF antennas, unless proper installation guidelines are followed.

Using fundamental antenna theory, and installation experience we have gained over many, many years of dealing with HF antennas may provide the answers you are seeking. No engineering formulas and complex theory here, just practical information gained from customers themselves, in addition to our own test results and operator knowledge as hams.

You're looking for the "how, why and what to do"! Some of the following points will be very basic for some of you, but in talking to many hams of all levels of experience, we hope you will find these points and suggestions useful and time saving.

A. Slopers (quarter wave) have a unique set of installation requirements compared to the typical half wave dipole. Basically, they require operation on a support/tower (35 feet or higher) with an HF size beam on top to act as a "capacity hat", sort of like an upside down vertical where the beam elements are like the radials of a ground mounted vertical. Also, there needs to be a good ground return path down the tower, and the sloper needs to be "in the clear". Metal guy wires that are not "broken-up" with insulators, and other wire antennas on or near the tower can cause serious problems (SWR and tuning). SWRs are most likely going to be a problem if these precautions are not considered. Sometimes, an external wide range tuner can help. It has been written that it's a lucky thing for a sloper to work correctly at all, since the support tower, guy wires and other attached antennas are a part of the sloper circuit. And, that can be true. However, with proper installation, a quarter wave sloper can be a very effective low band 160/80 meter DX antenna for those with limited space and lower height capabilities. We have many reports of multiple DXCC awards on these bands with quarter wave slopers.

B. Dipoles are a relatively simple design and usually easy to install and tune with good SWR, but they too require some thought for proper operation. Dipoles operating on 20 through 10 meters should be at 30 feet, or more, in the air. Dipoles operating on 160/80/40 meters should be at least 40 feet in the air for good SWR and at least average performance. Of course, there are exceptions to these numbers based on the customer "site". Higher heights on the low bands significantly improve performance. We have many customer reports of good operation at lower heights, but that depends on how high the "site" is electrically above ground at what's under the antenna. We can't predict that. Even at decent heights, both slopers and dipoles need to be in a clear "site", electrically uncluttered. See " Location" below.

C. Site Location. These antennas need to be as far as possible from any surrounding metal objects. Our tests, and those of customers, show that any antenna wire should be at least 15-20 feet from gutters and metal house siding or fascia. Metal guy wires should be "broken-up" with insulators at non-resonant lengths. Odd as it may seem, attics have a certain capacity characteristic (attic wiring and HVAC ducting) and antenna wires should be no closer than 10-15 feet from any roof top, even if it's a nonconductive roof material. Antenna wires should be at least 20 feet from other similar frequency HF antennas, even verticals.

Power lines must be avoided at all costs, and any antenna that may fall as a result of a storm or support failure must be positioned to NEVER fall across a power line. To reduce power line noise pick up, the antenna must be as far as possible from a line run. 30 feet, or more, is preferable.

A low frequency dipole (80/40 meters) can be put up to within 10 feet or so under a higher frequency (20/15/10 meters) beam with little if any problems. In an inverted-V configuration, the end of the wires should be about 8-10 feet, or higher, from the ground. The center feed point of an inverted-V should be offset from a metal support or tower leg by about 18 inches, on a nonconductive arm, to minimize couplingand thus higher minimum SWR. It is also IMPORTANT to note that antenna wires should not touch, or come closer than about 4-6 feet from any tree branch/limb or leaves. This may not be readily known but they can really upset resonant frequency or SWR.

If a dipole is fed with balanced line, the balanced line itself should be at least 6 feet from any metal objects, throughout the length of its run. It should never touch any metal, like window or door frames, as it enters the property. Of course there are exceptions, but this is generally the case. Close coupling of any metal to balanced line can significantly upset the system. Also, balanced line running down along side a metal tower leg or mast can cause serious coupling problems. If the balanced line is feeding a tower mounted dipole, it should come away from the tower at about a 45 degree angle and not near any guy wires or other wire antennas.

D. Attic installations. We have many successful customer reports of attic installations. HOWEVER--and this is a BIGGIE! Attic installations and performances (SWR) are unpredictable due to the fact that HF antennas in attics can be upset by attic wiring and heat/air ducting being nearby. Also, metal gutters and roof/wall material can be a factor. The height above ground (single story, multistory) is also an important consideration as with any "site" conditions.

Depending upon your residence, RFI coupling into stereos, TVs, burglar alarms and even garage door openers can also be a problem, particularly with high power. Due to the coupling effect of attic installations, an external wide range tuner is usually required for proper SWR tuning and operation.

These ideas are passed along to answer some of the questions we get concerning HF wire antenna installations. It is not meant to get into antenna theory and design as there are volumes and volumes of antenna books available from a variety of sources. However, it is interesting to note that in all those volumes, there is very little about antenna installation "site" information. There is information about antenna height Vs angle of radiation and patterns, but that's about it. It's probably because all the theory assumes antennas that are theoretically "in the clear" and in free space (called isotropic). The problem is, that's usually not too practical!

(There is NO commercial content here. These thoughts apply to ANYONE's HF wire antennas (good info for beams too). Pick whichever one is best for you.)

Welcome to HF, and have fun!

Don, W8AD, Alpha Delta Communications, inc.

Member Comments: