Multiband doublet antennas

This excellent article covers all aspects of designing a resonant loop antenna, examining gain and radiation patterns, and describing practical notes on how to build this antenna. This antenna covers 80 to 6 meters with low feed point impedance and will work with most radios, with or without an antenna tuner. It is approximately feet long, can handle the legal limit, and is easy and inexpensive to build.

It is similar to a G5RV but a much better performer especially on 20 meters. It is a half-wave long on the lowest frequency, and is fed from a coax cable through a transformer inserted in the wire at one-third from one end Stealth Multiband Vertical A vertical antenna for 40 and 80 meters band, using a telescoping fiberglass fishing pole. It has been specially developed as a highly efficient antenna for dx-pedition and portable use. Rotatable Dipoles Portable, and shortened with loading coils rotatable dipoles for 6 meters, 20 meters and multibands.

To build this antenna you need a lot that is at least feet across. By Karl-Otto Muller, DG1MFT An effective 3 band Wire DX aerial A 3 band dipole for 10 15 and 20 meters band, easy to build, and that can be easily setup in any occasion, inclunding field days or portable operations Delta Loop Antenna A multi band inverted delta loop antenna project that can be used from 40 to 10 meters band with full details and analysis of antenna performances on each band, document includes EZNec reports and setup pictures 1.

If you could only put up one antenna, this would be it. Project by N0KHQ. The 20m to 10m, antenna is simple and cheap to make, and has a performance that matches commercial antennas but at cost considerably lower. The design was purposely based on a telescoping fibre glass fishing rod as this allows it to be easily stowed away in the car. Tuner is required. The antenna features double-coaxial-cable-wound traps having lower reactance and a higher quality factor Q than earlier coax-cable traps by W8NX [ Hits: Votes: 5 Rating: 6 ] Another vertical antenna for 30, 40 and 80 meters - This article is to describe a multi band DX-dedicated antenna offering a minimum of compromises such as lossy trapsfor the hams not having any high-support [ Hits: Votes: 4 Rating: 3.

The open-wire feed line dipole antenna is easy to install and offers surprising performance on several bands. You can install it in almost any configuration; it does not have to be strung in the traditional horizontal flat top [ Hits: Votes: 2 Rating: 10 ] Coaxial Traps for multiband antennas - A new perspective on the analysis and design of this popular antenna element.

This antenna can be configured for several bands and can work in 3 or 4 bands mode. Can be used in restricted space lots. Consist of 6 vertical elements and 6 base radials with a single 50 Ohm feed line. The dipoles are resonate on the following bands: 6 meters, 10 meters, 12 meters and 17 meters.

Performance considerations, detailed pictures and construction notes. Operating Bands: 40 thru 10 meters with tuner [ Hits: Votes: 5 Rating: 8. He documented the design and construction plans for a portable antenna that can be built with relatively ordinary components [ Hits: Votes: 16 Rating: 7. This web page contains pictures, performance data, and enough construction details so you can homebrew your own. Ham Radio operators review new sites every day sincefor potential inclusion in the Directory, and to evaluate the best place to list them.

Multiband antenna Multiband Antennas.As open wire feeder is able to operate with levels of standing waves and effectively becomes part of the antenna, it is able to operate over a wide band of frequencies. As a result, the doublet antenna forms a very convenient multiband antenna and it is often used at HF where a number of different HF bands need to be covered, and it is relatively popular with radio amateurs where it enables several bands to be used with a single antenna.

The doublet antenna is essentially a balanced system and each half of the top plus each wire in the feed line must be equal in length. The antenna top is not cut to resonate at any particular frequency unlike the half-wave dipoleand any length may be chosen to suit an individual location. The key to the doublet antenna is the form of feeder used. Open wire or balanced feeders are able to operate as part of the actual antenna itself, not just feeding the power from an unbalanced source.

multiband doublet antennas

The balanced feeder or open wire feeder is able to operate with standing waves along its length. It provides the capability for very low loss, provided it does not pass near other objects that might cause imbalanced.

Balanced feeder is often used on the HF bands. Read more about Balanced Feeder. Standing waves are a feature of radiating wires, but in the case of the open wire feeder, it consists of two equal length close spaced wires.

As these carry equal and opposite currents their radiation cancels. However the feeder still remains part of the overall antenna itself. However it is found that the top section, i. The doublet antenna can operate over a wide range of frequencies and as a result the radiation pattern will change according to its electrical length with respect to the number of wavelengths, or part of that it represents.

As the electrical length increases, i. As the electrical length increases, so the phasing of the fields around the radiating element mean that the radiation changes from a figure of eight pattern for a half wave top radiating element to a pattern that has lobes that increasingly move towards the axis of the doublet antenna. The feeder can be either open wire or what is termed ladder line.

Also the length of the feeder can be cut meet the requirements of the installation. When feeding an antenna of this type it is found that it can present an impedance over a wide range. Accordingly it is necessary to use an antenna tuning unit to ensure that the transmitter itself is presented with the required impedance. This can be measured using an SWR meter. The antenna tuning unit used should be able to match impedances over a wide range, and it must also have a balanced output connection.

If it does not, then an external balun is required so that the unbalanced to balanced transition is present. Baluns can be bought or made. Essentially they are simple in their construction provided that the right components and tools are available. Particularly key is the former on which the balun is wound. Typically this is a torroid and it must have the required RF properties and RF power handling capability.

This provides an adequate match for many ATUs with only unbalanced output connections.Your JavaScript appears to be disabled. JavaScript is necessary for various functions, such as order checkout, to operate on this web site. Please ensure that JavaScript is enabled. Your web browser appears to be out of date.

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Using a tuner, they are usable to 30 MHz and come complete with the wire elements, ladder feedline, center T support, and end mount brackets. These antennas are built using the highest quality components.

Stainless steel hardware is included. Often, a balun is suggested for multi-band dipoles; however, the best balun to use for this application is a ratio. The baluns provide better balance, have lower loss, and are more tolerant to load impedance and balance variations than other baluns. A tuner balun is not included in the dipole antenna kits and is available separately. The dipole center T support has pre-drilled holes for the attachment of the wire elements, feedline, and support or messenger lines.

The center support top hole is used for the attachment of a "messenger line" that can be strung above the antenna wire and is used to provide support for the antenna wire and feedline.

What is a Doublet Antenna

The use of the messenger line, which is strongly recommended but not included, will reduce the stress on the element wires and keep the antenna from stretching over time, which will change its resonant frequency. This line can be thin Synthetic Textile rope available from DX Engineering, which has a high breaking strength. Ideally, it should attach to the same structure used for the dipole, only above it, forming at least a 30 degree angle between the dipole and the messenger line.

For further information and to decide the amount of rope you will need, please read the included instructions and check your wire antenna area of construction. Note: Whenever the DX Engineering "Documentation" tab is available, please look at the associated files for additional product information. When you lack the room for more than one antenna or need a multiband antenna for band agility, consider one of these DX Engineering Multi-Band Dipole Antennas as an elegant and economical solution!

DX Engineering Verified Purchase. Was this review helpful? Yes No. If you feel that this review is inappropriate and should be removed from the site, report it to us by clicking the "Report Abuse" button below. Date: September 02, Length, Each. Diameter, ft. Roll, Each.

What is a Doublet Antenna

We do not sell email addresses or other private information. Privacy Policy. Outdated Internet Browser Detected Your web browser appears to be out of date.Tune Around! Project also includes a novel way of getting the rf to and from the shack using coax rather than ladder line. Shown with standard TV type ohm ribbon line. If you don't have room for the or 80 meter version Just remember, don't operate it on a lower frequency than it was designed for Always check swr at low power before attempting.

It can be installed in the horizontal fashion or inverted V style. Get it up as high as possible and have fun! Remember when working with twinlead Flat TV feed type don't use over about watts of power to be safe.

For higher power, use the heavier, ladder, open or window type. The radiator: After you have determined the total length of the horizontal section of the antenna, lay that amount of your antenna wire out and cut it in exactly in half. This will give you two identical lengths for each half of the antenna. It is suggested that you use 14 or 12 gauge wire. You can use smaller size wire but it will tend to break easier with longer antennas due to weight of ice, snow, birds, wind loads, etc.

See example drawing below:. Use your imagination and ham engineering. It should be of a size that will allow the antenna wires to be attached to it from each half of the antenna with strain relief for each wire including the feedline. Your feedline also needs strain relief.

multiband doublet antennas

In the drawing above, they are the heavy black lines going across the twinlead. If you use TV type twinlead, this will be a must. TV twinlead is very fragile and can break easily from too much strain. The weakest point on the twinlead is where the conductors come out of it on the ends. The wires are very small inside and break easily. Each half of the antenna can go thru holes drilled into the center insulator This type of arrangement provides some strain relief for the antenna wires using the mechanical pressure of the wire against the center insulator.

It is important that there are no sharp edges where the wire enters or exits the holes.Forgot Password? You can also enjoy multiband performance without traps, coils, fans or other schemes. Simply cut two equal lengths of stranded copper wire. These are going to be the two halves of your dipole antenna. Just make it as long as possible. Feed the dipole in the center with ohm ladder line available from most ham dealersand buy an antenna tuner with a balanced output.

Feed the ladder line into your house, taking care to keep it from coming in contact with metal, and connect it to your tuner.

Multiband antenna

Use regular coaxial cable between the antenna tuner and your radio. A foot dipole of this type should be usable on almost every HF band. Shorter versions will also work, but you may not be able to load them on every band. Just apply a signal at a low power level to the tuner and adjust the tuner controls until you achieve the lowest SWR reading. Anything below is fine. You may discover that you cannot achieve an acceptable SWR on some bands, no matter how much you adjust the tuner.

Even so, this antenna is almost guaranteed to work well on several bands, despite the need to retune. The reason has much to do with convenience. You must keep it clear of large pieces of metal a few inches at least. Wire antennas fed with coaxial cable must be carefully trimmed to render the lowest SWR on each operating band.

With a ladder line dipole, no pruning is necessary. Simply throw it up in the air and let the tuner worry about providing a low SWR for the transceiver. Whichever dipole you finally choose, install it as high as possible. Secure Site Login Forgot Password? Random Length Multiband Dipoles You can also enjoy multiband performance without traps, coils, fans or other schemes. Click on the images below for examples. Back to Top Having Trouble? Donate Now.I use an old favorite multiband antenna on forty and eighty meters - the center-fed inverted V dipole, fed with true open wire feedline -sometimes known as "tuned feeders".

Nothing new about this, except it seems to have been forgotten by many. One rule-of-thumb with antennas is that one which is optimized for one band, is superior to a multiband antenna, all other things being equal.

I believe this antenna comes the closest to upsetting that rule. And it is very efficient due to the ultra-low loss inherent to open wire line - the only significant loss is in the impedance matching network - my Johnson KW matchbox. I need to measure this loss, but I know it does not cause any noticeable component heating after five minutes of a kilowatt through it. A 3D pattern of aggregate horizontal and vertical polarized radiation of the inverted vee over real ground is shown above.

multiband doublet antennas

Amazingly, according to the EZnec model, it approaches being omni directional. Sidebar: This antenna is very different from antennas fed with coax which require a tuner in the shack. If you are after efficiency, coax should never be "tuned" except in the case of minor mismatch, for instance changing a 3. Rule of thumb - if the antenna produces more than VSWR, and you want to feed it with coax, match it to 50 ohms with a network at the antenna, not in the shack.

Many hams seem to believe that "resonant" antennas are fundamentally superior to those requiring a matching network. This mistaken belief may stem from the correct idea that using a transmatch on non-resonant coax-fed antennas may please the transmitter, but will radiate poorly. The important difference is that most coaxial cable available to hams works well only when operated close to it's characteristic 50 ohm impedance - losses rise rapidly as the load departs from 50 ohms.

The coax actually converts part of your RF power to heat - instead of transferring it to the antenna. AM broadcast stations are designed to be very efficient - and almost invariably use a non-resonant vertical tower fed thru a low loss matching network with coaxial cable. On the other hand, a well -designed open-wire line can operate with tremendous SWR and still introduce less loss than even well-matched 50 ohm coax over long runs.

Balanced line feeds a balanced load! We've all seen balanced line feeding off-center fed antennas in the old handbooks - but remember, "single-wire" fed antennas were also used. Feedline radiation wasn't thought about much. For balanced line to function correctly, not radiate it must maintain equal and opposite current in each conductor. In order to do this, the load antenna must be balanced with respect to ground and other conductors.

IF the load or source is unbalanced, the currents are unequal, and the line will radiate - a normally undesirable condition - the line radiates energy all the way down to the shack, and into it, causing RF "hot" surfaces and RF in audio and computers. For the antenna to be balanced, it must be very close to symmetrical in all respects - length and height above ground - think ideal dipole.

multiband doublet antennas

An unbalanced antenna can be fed through a balun, but these can introduce significant losses when operated o u tside their design impedance. A balanced antenna fed with balanced line.

Building a Multi-Band Dipole

Although one does not need a SWR to achieve good transmit efficiency, the transmitter 3cxs in my case may operate better with low VSWR. Particularly on 75 meters, getting a good match across the band can be impossible with a conventional half wave dipole fed with coax. For years the handbook has shown the foot center fed "doublet", using open wire line to be a recommended multiband antenna.

I think that if you can deal with the open wire line routing issues, and use an efficient matching network tuner it may well be the very best multiband antenna.

Balance is important for this type of transmission line to work as intended - each side must have the same current flow. My configuration is inverted-vee style with the apex at 80 feet, the ends about 25 feet high. When I constructed it, I used a capacitance meter from each side to ground while adjusting end heights to get the same C with respect to ground. In simple terms, true open wire line sometimes called tuned feeders has lower loss for two reasons:.

The range of average impedances it operates at is generally much higher, with more voltage and less current. The reduced current lessens the ohmic losses in the skin-effect surface of the conductors. This tradeoff places more stress on the insulating materials, which must withstand more voltage without arc-over and must not have much leakage resistance between conductors. If you are a student of the Smith chart, you can see that even a 50 ohm load is transformed into a significantly higher impedance, when using a ohm line.All-Band Doublet L.

Cebik - W4RNL. The all-band doublet horizontal wire antenna has a history almost as long as amateur radio itself. Despite all the words and diagrams in handbooks over the years, newcomers still send me questions about the antenna.

I have collected the questions and boiled them down to 10, all of which have many variations. The goal in tackling these frequently asked questions is to help newer hams erect a successful antenna system. What is an all-band doublet? The all-band doublet is actually an antenna system and not just an antenna alone. The horizontal center-fed wire forms the antenna proper, which accounts for the radiation of transmitted energy and the reception of incoming energy.

The parallel transmission line transfers the energy from the antenna to the antenna tuner or antenna-tuning unit, the ATU or vice versa.

We insert the tuner because the impedance that shows up at its terminals will vary widely from one band to another. So we need a way of matching the impedance at the tuner terminals to the standard Ohm input and output impedance of the transceiver. Table 1 shows common doublet lengths that have appeared in handbooks since the s. It also shows the ham bands covered by the antenna. However, there are limits that we shall explore as we proceed through the questions.

What is the difference between a doublet and a dipole? Conversationally, the term "dipole" often refers to any antenna that looks like a dipole, that is, a center-fed wire antenna with a feedline going to the shack.

In this context, we also tend to call any end-fed antenna a Zepp although there is a center-fed extended double Zepp and to refer to any off-center-fed antenna as a Windom although the original Windom had only a single feed wire.

In more precise terms, the coax-fed dipole that we sometimes set up for single-band use is a more complex antenna than its appearance suggests. The center-feedpoint is obvious from the position of the feedline. It is resonant since the feedpoint impedance is almost purely resistive, with little or no reactance. Finally, it is a dipole because, as Fig. As a result, the current is maximum at the center and minimum at the wire ends.

The dipole undergoes only one transition in charge and in current from the center to the wire end. When we use the antenna on many bands, it becomes electrically longer, because the length of a wave grows shorter with rising frequency. Hence, the charge and current patterns do not satisfy the dipole conditions above the lowest band or two. Since the current does not follow the dipole pattern, the charge density is also different from a dipole.

In this case, there are many transitions and the current is not maximum at the center feedpoint. The term doublet is more generic and less fully descriptive than others. However, it also has a history. In the s, it served as a label for a center fed wire with a special feed system.

Later, the antenna was renamed the delta feed and the term doublet became a generic term for center-fed antennas of any length. Hence, our antenna is an all-band doublet. Do I need to measure the wire for precise resonance on the lowest band?

In a word, no. When we set up a resonant monoband dipole, we want it to achieve resonance or the lowest possible SWR with our coax cable feedline.


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