Reviews on Arrl Antenna 4 Book Boxset 1144

Introducing the "All-Ring" Doublet:
What the Student and the Instructor Should Keep in Mind

L. B. Cebik, W4RNL

Possibly too many new hams embarking on their first HF adventures think just of resonant dipoles fed with coaxial cable and plugged straight into the transceiver's output connector. Many end up with a mass of wires in the back yard as they try to make separate antennas for 80, 40, 15, and 10 meters. Others think that they are restricted to only one band because they have room for but ane antenna. Too few modern Elmers have the personal feel to guide new HFers into one of the oldest ham antennas of all: the all-band doublet.

It may be useful to review what it takes to go the doublet on the air finer. The data comes in two parts: 1. information that every doublet user should have initially, whether a student or an experienced ham, and 2. opportunities for the teacher to assist students and new hams in gaining some applied knowledge about problem solving, parts acquisition, and a number of other areas that stop some newcomer projects in their tracks. An all-band doublet is a rather refined antenna organisation when looked at in item, but it is besides relatively like shooting fish in a barrel to get on the air with information technology. If the student runs into difficulties or has questions, the instructor tin help him or her work out the answers. There are many opportunities for advanced Elmering with the all-band doublet

The Basic Doublet Antenna System

Equally shown in Figure 1, the bones all-band doublet antenna organization consists of three parts: the antenna proper, the feedline, and the antenna tuning unit (or transmatch).

ane. The Antenna: The antenna proper consists of a length of copper or copperweld wire, with a center feedpoint. Three pop lengths for the antenna are these:

a. 130-140' (best, if you lot have the room and want the strongest results on fourscore meters.

b. 90-110' (works 2d all-time on fourscore meters, with good results on all other bands).

c. 65-75' (good for 40 meters through 10 meters, but not for 80).

Discover that the precise length is not critical. Much more than critical is getting the doublet equally high as you peradventure tin. Although the antenna will piece of work at low heights in the 20-25' range, it does much better (specially on 80 and 40) when it is higher than 35' up. You can utilise bachelor trees for back up, or yous tin can even build your own support poles or trusses from designs in the ARRL Antenna Book.

Many inexperienced hams volition need guidance in the pick of materials. Obviously, #14 stranded wire, readily available at stores like Radio Shack, volition fill the bill. However, if in that location is a local hamfest, you may want to guide the new ham in the buy of copperweld wire. You may also have to guide him or her in its peculiarities, especially how to keep it straight while trying to assemble the antenna. Insulated copper wire will too work well if it is sufficiently strong. The inner ends will require insulation stripping to make connections, but the far ends may be left insulated. The twisting of wires at these ends to make a loop for the support line volition innovate no significant changes to the antenna's operation.

A second area where guidance can be critical is in the selection and utilize of antenna supports. Abode-made trusses and their guying are not elementary matters. Neither is trying to get a line over a branch 40' or more than upward a tree. The many techniques for launching a line often depend on local talent, whether that talent is tree climbing, bow-and- pointer, fishing rod, or slingshot. Guide the new ham to the local talent and be sure that safety lessons accompany the talent.

Of course, the ends of the wire need to be insulated from the back up, so you will need terminate insulators and rope for the task. A practiced 1/4" sun (UV)-resistant constructed cobweb rope will hold up almost antennas unless they are stressed too tightly.

Suppose that the antenna will not quite fit the infinite available. One standard technique of reducing the real manor needed is to set up upwards the doublet in the inverted-Vee configuration. This version of the doublet tends to circularize the design, only reduce overall gain of the antenna at virtually every frequency of use.

Consider angle the elements instead (if supports are available). Drooping ends are the well-nigh common version of this arrangement. However, setting upwardly the antenna equally a "Z," with all parts of the antenna wire every bit high as possible, often provides amend performance. Drooping ends, and even ends bent in the same direction, provides some radiations cancellation, especially on the lowest bands of use, while the zig-zag version--if not also radically Z-ed--tends simply to bend the pattern'southward directions.

Once more, a newcomer may need some guidance--or even simply a 2d pair of optics--to see conspicuously all the possibilities and potential problems of laying out an antenna within the confines of his or her chiliad. What makes a good support, what directions the wires should go for maximum communications, and what hazards to avert are all questions calling for experienced communication. However, effort not to take over the unabridged task from the newcomer.

ii. The Feedline: The second chemical element is the feedline. For this antenna, we use a parallel transmission line because information technology has very low losses, no matter what the SWR (within reasonable limits). 300-Ohm TV ribbon line will work, but it is non the strongest. Most ham dealers can get 400-Ohm or 450-Ohm vinyl-coated transmission line with larger wires. Completely open ladder line, with just insulated spaces, also works well just is less common.

Guidance in the pick of feedline may also be needed, especially in knowing which inexpensive and weak lines to avoid. If there is a local hamfest that is likely to draw a reputable antenna wire and feedline dealer, helping the new ham make his or her purchases is an human action likely to be appreciated for years to come.

Unlike coaxial cable, which you may run close to whatever object, parallel manual line should be as gratis and clear of objects as possible. If the line must be brought down parallel to an object, such as the wall of a firm, utilize insulated spacers to go on the line several inches away from the object. Avoid bringing the line well-nigh metal gutters and down spouts, power lines, conduits, or other metallic objects. Close proximity to metallic can disrupt the balance between the wires of the feedline, adversely affecting its performance. Wherever the line must change directions, keep the angles shallow and, if at all possible, proceed the line at right angles to the antenna wire.

Apply special intendance when attaching the feedline to each side of the antenna wire eye feedpoint insulator. Be sure that connections are mechanically secure, and so solder the feedline wires to the antenna wires. Test the connections for movable wire bends that may crusade a break while swaying in the wind. Recently, some ladder-line "grabber" center fixtures accept appeared on the market to secure the ladder line to the antenna wire and reduce the danger of breakage: they are well worth the investment.

Ane special problem deserves special attention: getting parallel feedline into the shack and over to the antenna tuner. In that location are nearly as many ways to solve this problem as at that place are all-band doublet installations. The type of solution used depends largely on where the feedline enters the firm.

If the feedline enters at a window, one can bring it through the window frame or through a board installed at the base of the window. Both have advantages and disadvantages. Bringing the line though the wooden window frame defaces the frame. Using a lath on which the bottom section of the window closes requires special means to ensure insulation and security around the window. In each case, one can use a pair of bolts spaced virtually the same distance autonomously as the wires and brand separate indoor and outdoor attachments. This characteristic is of import, since information technology permits detachment of the feedline when electric storms are imminent or when going on holiday.

Feeding a parallel transmission line through a wall calls for even greater care. One elementary system (among many) uses a curt length of PVC run through the wall and atmospheric condition sealed around the edges. Some hams center the transmission line in the tube and hold information technology in place with fiberglass insulation. Others use plastic spacers with a middle cutout to hold the line in place and seal the tube. There are many variations on this theme, but the old idea of simply slamming a window frame down on the transmission line at the window should be discouraged, especially with metal window frames. In all cases, there should be a way of disconnecting the manual line out of doors and grounding it.

Routing the feedline within the business firm or shack calls for equal intendance. Ideally, the tuner should exist equally close to the line exit point every bit possible. Feedline should not be only drooped on the flooring or haphazardly tacked to the walls and ceiling. Spacing from invisible metal in the wall cavities is every bit essential indoors as is spacing from outdoor metallic objects.

Helping new hams analyze where duct piece of work, house wiring, telephone wires, and metal plumbing pipes may be located in house walls is another loonshit of aid too frequently disregarded. Many new hams are equally initially uneducated about house structures and utilities as they are almost apprentice electronics. Showing the pupil how to look at house fixtures, outlets, switches, telephone and cable connections, and plumbing routes and to apply these signs to make practiced estimates of their routings through the firm may be a really enlightening experience for the student.

3. The Antenna Tuning Unit or Transmatch: The "antenna tuner" is a network for transforming the impedance that is present at the shack end of the transmission line to another value, normally fifty ohms. An all- band doublet shows a different feedpoint impedance at each frequency of operation. The verbal length of the antenna relative to the frequency will largely determine that impedance. The feedline will transform that impedance continuously along its length, repeating values every half wavelength of line. Since most transmission lines have a velocity factor, a half wavelength of line will be shorter than a true half- wavelength for the frequency of interest.

All of this together means that the exact impedance presented to the antenna tuner will vary from band to band and from ane antenna installation to another.

Most antenna tuners use unbalanced networks. The almost popular network used in commercial tuners is the series C, parallel 50 Tee network, schematically shown in Figure 2. The popularity of this network stems largely from the fact that it is the virtually economical to produce and from the relative ease of tuning it to an adequate low-SWR friction match.

Unbalanced networks employ a 4:1 transformer or balun to allow for the utilise of counterbalanced feedlines. This feature often means that the antenna tuner settings that produce a depression SWR between the tuner and the transceiver may not give the highest efficiency of power transfer. However, for most general purpose communications, efficiency will be adequate.

Building one's own antenna tuner or transmatch is a skillful introduction into the satisfactions of dwelling house construction. Students may need guidance in the choice of parts, many of which are available these days only from surplus outlets or at hamfests. Helping the pupil select parts that are suitable in their range of values and their power-handling ratings without paying too much is an invaluable service. Another avenue of help is request local social club members to search their junk boxes for components they may exist willing to sell or donate to the cause of aiding a new ham.

A second avenue of guidance is helping the new ham select a suitable commercial tuner, if that is his or her favored route. Interpreting specifications, evaluating features, and didactics the educatee to look at the tuner as a long-term investment that can exist useful many years down the road are all important activities that teach past example the practiced art of reading ads and brochures and making the best possible option of equipment for one's present and future needs.

Since antenna tuners do not vesture out unless severely driveling, used transmatches should be as skilful every bit new ones, and perhaps less expensive. In one case more, helping a new ham scour a hamfest for the best used equipment available--showing him or her what to expect for and what to wait out for--may be a real service that has long-term benefits. New hams also need a niggling help in learning how to bargain downward a toll.

If the all-ring doublet is to exist a long-term antenna for the new ham, and if home-brewing is an interest, and so the best antenna tuner may non exist the C-L-C network with a balun to handle balanced lines. Instead, there are circuits in the ARRL Antenna Book and elsewhere for link-coupled antenna tuners that have balanced outputs ready for the parallel feedline. Finding the right scroll stock and capacitors, nonetheless, may be a off-white-sized challenge these days.

Adjusting the All-Band Doublet

Using the all-band doublet requires just a fiddling more than work than using a resonant dipole. The first job is to find the correct antenna tuner settings for each band you plan to employ. However, once y'all have established these settings, yous can make a chart and return to the settings, with only a moment'southward tweaking to ready the antenna perfectly.

Since the most common tuner is the C-L-C Tee with a balun for balanced transmission lines, let'south run across what the set-up for it consists of. Kickoff, use a low ability setting for initial tune-upward. Second, for each band, notice an empty place to practise your tuning in order to minimize QRM. Tertiary, read the tuner manual to run across if at that place are whatsoever recommended initial settings for the controls.

The side by side step is to apply low power and observe the settings of the controls that allow you to achieve a 1:ane SWR. Tape the setting. Now increment ability to the level at which you intend to operate. You lot may have to tweak the settings but a fleck.

Repeat the process for each of the bands. If y'all have never used this kind of set-up earlier, you might practice moving from ring to band and so that you lot do not forget to check the settings and make last adjustments before going to full power.

For each band, also cheque how far up and down the band you can move the transmitter frequency without exceeding a 2:1 SWR. Make notes on whether the settings are wide or abrupt for each band. Sharp tuning often indicates either of a high SWR or a high level of reactance at the tuner antenna terminals--or both.

On some bands, you may find more than i set of control settings that will give a 1:1 SWR. For C-L-C tuners, the rule of thumb is to employ the setting with the higher output capacitance, which usually coincides with a lower value of inductance. These settings are usually higher in efficiency. Even so, you should listen to signals on the band with each set of command positions and use the ones that yield the stronger signals--if whatever difference can be detected.

At the other extreme, you may discover that on some bands, at that place are no settings that will produce a ane:1 SWR. This condition ordinarily means that the impedance at the antenna terminals of the tuner has too much reactance, either capacitive or anterior, and the tuner cannot both compensate for it and too cease up with a correct value to make the match perfect.

The easiest method of overcoming this problem is to alter the feedline length past patching in a half-dozen' to 10' section of line between the tuner terminals and the "regular" line. Since a transmission line is an impedance transformer along which the values of resistance and reactance are constantly changing (if the SWR is initially greater than one:i), changing the length of the line changes the values of resistance and reactance presented to the tuner.

Sometimes, the new line length will work with all bands. In other cases, keeping the "patch-in" department handy is necessary for a few bands.

For new hams, these procedures are often mysterious, and a "doom-and-gloom" factor can set in as before long as they discover that everything is not perfect on the beginning try. Reassuring them and showing them a few tricks of the trade can become a long toward increasing their conviction that they can tackle new challenges and overcome them. As e'er, notwithstanding, allow the newcomer handle the controls every bit much as possible.

What to Expect from the Doublet

Initially, newcomers are simply charmed to hear signals on the bands and to be able to make contact with some of them. Eventually, however, they volition come with a multifariousness of questions. Why can I hear the 1s and 2s, simply not the 4s and 5s? Why exercise I hear near-past stations on 80 and 40, but lots of DX on fifteen and 10?

Part of the answer lies in the nature of the ham bands, simply part of the reply as well lies in the antenna itself. An all-band doublet produces a unlike radiations and reception design for each of the ham bands. In addition, the bending at which the radiation goes out and comes in most effectively varies from ring to band, with the college bands mostly having lower angle radiation than the lower bands. (This accounts in part for better DX results on the upper bands.)

Although providing a complete fix of patterns for all versions of the doublet would require lots of space, I can at least provide a small-scale rogue'south gallery of some patterns.

Permit's assume that nosotros have a 135' doublet (plus or minus 10') at about l' in the air. What sort of patterns would this antenna brand for each of the Novice CW bands? Making allowances for the highly variable effects of terrain in the general region and the ground clutter that surrounds near homes, nosotros can expect something like the following patterns for each ring. Remember that the upper azimuth pattern in each ready assumes the doublet is aligned from left to right. It is taken at the height of maximum radiations (except for 80 meters). The lower pinnacle patterns are taken along the strongest lobe of the antenna's pattern on that band, whichever way that lobe might be pointed. Azimuth patterns generally tell the states in which direction over how wide a span our signals become, while elevation patterns tell usa at what angle almost of our signal hits the ionosphere, to be reflected back toward world and a receiving station.

The 80-meter azimuth pattern is taken at an superlative angle of 45 degrees. As the summit blueprint shows, virtually of the radiation is above this angle. Some hams telephone call the relatively low dipole a cloud- burner. Although this is not a DX antenna, in that location is enough of useful radiation for all kinds of fantabulous 80-meter QSOs.

On 40 meters, the all-band doublet has a narrower pair of lobes, but the radiated signals in the primary directions will be stronger (and reception more sensitive). The height angle of maximum radiations is 39 degrees. However, note that at that place is a lot of energy existence sent out (and received) at lower angles. Hence, the possibilities for DX improve. Withal, the antenna proves most useful for cross-country QSOs ranging from 800 to 2400 miles, depending on the fourth dimension of day. These will mostly exist broadside to the antenna wire.

If we had installed the antenna as an inverted-Vee, with the wires sloping downward from a central support, there would be a few modifications to the pattern. Instead of a peanut, the azimuth pattern would be more oval, giving more than reception and less rejection off the ends of the antenna. The angle of maximum radiation would also be merely a flake lower, although maximum signal strength at the peaks of the major lobes would be downwardly just a bit. For general operating, the differences are not probable to exist noticed without a side-by-side exam.

On xv meters, the antenna is 3 wavelengths long. Notation that there are iii major lobes on each side of the wire. The stronger outer lobes are about 45 degrees off broadside. The elevation angle of maximum radiation is well-nigh thirteen degrees, well down into DX territory. Since xv is a practiced DX ring, it would be prissy to align the antenna so that one of the major lobes points at a desired DX territory.

On 10 meters, the doublet is 4 wavelengths long, and at that place are four major lobes on each side of the wire in the azimuth blueprint. The elevation angle of maximum radiation has dropped to 10 degrees, and the antenna is capable of assuasive united states of america to work a lot of DX--if one of the principal lobes is pointed in the right direction. The main lobes are about 35 degrees from the ends of the antenna wire.

Newcomers are condign more and more than sophisticated about antenna patterns, since a few appear in almost every outcome of the amateur radio magazines. However, what the patterns really hateful may non be articulate. Instructing newcomers in how to utilize azimuth and elevation patterns volition help them make improve use of the large amounts of antenna information bachelor these days.

One especially of import lesson to teach is that all of these patterns have limitations, since they are generated by calculator rather than by actual measurements made of the functioning of actual antennas. First, the figurer modeling programs employ a level ground, which is not the terrain for many hams in the U.Southward. Hilly or mountainous terrain may vary antenna patterns by a significant margin. Second, the patterns assume a level antenna wire, with none of the droops, zigzags, and other shape imperfections we mentioned before. However, none of those imperfections will have a pregnant negative outcome on antenna performance. They volition just shift a lobe or ii past a little bit.

The best apply of patterns like these is to establish some very general expectations about antenna functioning. For case, we might look an azimuth pattern of the 100' version of the doublet to accept just 3 lobes on each side of the wire; and the 67' long version would show merely 2 lobes on each side. However, if the antennas are all at the aforementioned height, we would expect the superlative patterns to exist similar for each band.

Antenna Maintenance

Every piece of amateur radio equipment deserves regular preventive maintenance. The antenna arrangement is no exception. In fact, the antenna system--including the antenna proper, the feedline, and the antenna tuner--require special attention just because they seem then allowed to impairment.

Withal, here is a list of things that can happen to your antenna system that can adversely affect performance:

          1.  Antenna:           wire corrosion           wire breaks inside strong insulation           wear on support ropes or lines           wear or corrosion of solder joints at the feedpoint 2.  Feedline:           build-upwardly of dirt           subconscious breaks           changes in the nearby metals 3.  Antenna Tuner:           grit, dirt, tarnishing of the scroll           dirt between capacitor plates           dirty switches        

All of these items assume that nosotros take taken generally good care of everything.

The cure for all these evils is a regular maintenance plan to examine and clean everything earlier it causes problem. In addition, items showing wear can be replaced while the situation is under command, not during a contest or field day.

Proficient maintenance begins at the time of building the antenna and feedline arrangement. Raising the antenna should besides mean that it can be lowered. Hence, the employ of pulleys, middle-bolts, and other ways of passing the rope or support line is essential to a skillful antenna installation. Passing the rope over a crotch of a tree is a skillful method for finding the rope immovable in a couple of years, as the tree grows right over it.

Be sure that all connections between the feedline and the antenna wire are mechanically solid and well soldered. Do not rely on solder for the mechanical connection. In some parts of the country, it may be useful to seal the solder connection, since chemical salts in the air may interruption downwards the solder joint.

Even if y'all utilise a ladder-line "grabber" device, be sure that at that place are no sharp edges confronting which the line may rub and break. In fact, the first maintenance should be about 4 months after initial construction as a bank check to ensure that all piece of work was well done. Thereafter, a check at least once a year is wise.

Many hams wax antenna wires with 1 of the automotive waxes designed to get on metals. They also contain cleaners that remove dirt, grime, and some tarnish to the wire during reapplication.

Like measures also utilize to feedlines. Some doublet users accept noticed that the antenna tuner settings require a little change during pelting showers. While the water on the line may not create significant losses, it nevertheless pays to clean the feedline during a regular maintenance session. Over again, automotive polish applied to vinyl-coated feedlines not only helps shed h2o, but as well cleans dirt build-ups from particulates and chemicals in the air.

One ofttimes neglected area of maintenance is the point where the line enters the house. Because the temperature may be vastly different indoors relative to outdoors, the line and its insulation can undergo stress and vesture. If the passage is filled initially with fiberglass or a similar insulation to protect from drafts, the fabric can go packed with dirt and insects. Periodically changing the insulation-- and even the line section in this area--tin help maintain the antenna organisation at full efficiency.

The antenna tuner also needs a good periodic cleaning to remove dust and coatings that accumulate just from sitting in the living environment. A fine bottle-type castor (electric shaver type?) is good for catching dust between capacitor plates, as is some contact cleaner on a lintless rag. Nevertheless, be sure the cleaner is non-toxic.

Coils require special care. Many have tinned or silvered coatings, and tarnish tin be a problem. It can even degrade the contact betwixt the turns of a rotary coil and the wheel that contacts the turns. Try to make clean the curlicue with non-abrasive materials to avert removing the cease, since the copper underneath may tarnish fifty-fifty faster.

While doing a full general cleaning, inspect all connections. A proficient- looking solder articulation to a coax connector might reveal a weakness after a period of time. Switch contacts may need cleaning and fifty-fifty replacement. Tightening all chassis and instance screws (unless the education book explicitly says not to in some case) is usually practiced do, especially those screws that form part of the ground mutual of the tuner.

Instructing newcomers in skilful maintenance practices is essential in this world in which well-nigh all consumer electronics are marked "Do not open, No user parts inside." The unabridged apprentice station represents a new level of responsibility for the licensee. He or she is responsible for the care and budget of the equipment to ensure that it meets technical specifications fix by regulation. The simply fashion for many to meet this need with respect to transceivers is to transport them back to the manufactory for periodic servicing. However, nigh every ham is able to perform many of the maintenance needs of the antenna system. Setting good habits equally the new ham walks into the door of his or her new shack is to set a good habit for a lifetime.

The all-band doublet is so deceptively simple an antenna that information technology seems to beg for neglect--until it quits working or falls down. Yet, a regular schedule of maintenance one time or twice a year can make the antenna operate reliably for many years.

Of course, if the antenna does become a victim of weather, falling trees, or other accidents, replacing it is a straightforward exercise, made easier past having done it in one case already. Non only that, but replacement is easy on the budget. In fact, it may be impossible to find an antenna that does and so much for so footling equally the all-band doublet.

From Proceedings of the 1998 National ARRL Education Workshop, (Newington: ARRL, 1998), pp. 39-46 � 50. B. Cebik, W4RNL. Data may exist used for personal purposes, but may not exist reproduced for publication in print or any other medium without permission of the author.

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