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Good antennas
A beginner radio amateur finds it hard to orient himself in various antenna designs. Antenna books and the internet are full of various constructions. Good guides on which antenna to choose are the results lists, which indicate the type of antenna.
If we do not buy a ready-made antenna, we must know which dimension or material has a significant impact on the resulting properties of the antenna during construction. Osobne preferujem rokmi overené dizajny antén alebo antény s priamym napájaním koaxiálnym káblom z dôvodu:
- every matching circuit has certain losses
- due to the absence of measuring instruments, it is easier to tune one thing (the antenna) than two things (the matching element and the antenna)
- antennas with an impedance of 50 ohms at the feed point are broader bandwidth than the same type of antennas with lower impedance and matching circuit
- antennas with an impedance of 50 ohms at the feed point are much less sensitive to surrounding antennas and other objects
- simpler construction
- … however, the disadvantage is slightly lower gain and worse F/B (front-to-back) ratio
Simple HF antennas
A simple proven antenna is horizontálny polvlnný dipól. Pri napájaní v strede bude impedancia blízka 50 ohmom. Jej hodnota je závislá od výšky nad zemou a okolitých predmetov (budov).
The length of the half-wave dipole is calculated as: l = 150/f [m;MHz]
In practice, the length will be slightly shorter, which we will use for final tuning of the antenna in the given environment (we shorten it). End insulators can be purchased or made from old thick coaxial cable with Teflon dielectric. The wire must be strong enough to withstand the load.
Given that coaxial is an asymmetric feed and a half-wave dipole fed in the center is a symmetrical antenna, their connection should be solved with a 1:1 balun. Proper construction of the balun requires suitable materials and winding techniques – if these conditions are not met, balun nebude plniť správne svoju funkciu. Môžeme použiť aj komerčne dostupné baluny, pri malom výkone či portablovej anténe nepoužiť balun (neodporúča sa).
In higher bands, we can replace the balun with several turns of coaxial cable just below the antenna.
A popular shape modification is the dipole in the shape of invertovaného V-éčka. Vyžaduje len jeden vysoký úchytný bod a časť energie sa vyžaruje aj s vertikálnou polarizáciou, čo je výhodné pri DX spojeniach.
Viacpásmové dipólové antény offer a compromise option for operation on multiple bands. They are realized with traps (e.g. W3DZZ), tuned with a tuner (e.g. G5RV, Zeppelin), multiple parallel radiators or other feeding methods (FD-4).
A vertical quarter-wave radiator is an excellent DX antenna.. K správnej funkcii vyžaduje systém protiváh – radiálov. V prípade zemných (zakopaných v zemi, či na zem položených) platí, že čím viac a čím dlhšie – tým lepšie. Skutočne účinný systém tvoria desiatky až stovky radiálov. Výhodou je, že radiály sú nenápadné a nemusia mať rezonančnú dĺžku.
Unlike elevated radials, which must have a resonant length. Their advantage, however, is that we can achieve high efficiency with just one to four radials. The easiest to implement are two radials, which we first tune to the band as a dipole or inverted V at a low height (2-3m above the ground is sufficient). We then add a quarter-wave radiator and check the resonance and matching of the antenna. From the 40m band onwards, we can advantageously use telescopic poles made of fiberglass, making the antenna implementation very simple.
An excellent DX antenna for the lower bands is invertovaná L anténa. Je vhodná tam, kde nie je možné realizovať štvrťvlnnú anténu s plnou výškou. Popis takejto jedno- a viacpásmovej (160m, 80m a 40m) antény nájdete www.160m.de .
Material: purchased in local electrical installation shops, Amidon toroids at www.awas.sk or www.ges.cz, components or complete antennas also at www.ok5im.com
“From which antennas can not expect much?”, is a common question. These are mainly very short vertical antennas (height less than 0.1 wavelength in the given band) and various substitute antennas, such as balcony antennas.
The requirement to work on multiple bands can be solved with a multi-band antenna on a common boom. However, in home conditions, it is najrealizovateľnejšou smerovou anténou 2-elementová yagi. Materiál je relatívne dostupný a zhotovenie vyžaduje len bežné nástroje – pílku, vŕtačku, meracie pásmo, skrutkovače a sadu kľúčov.
Such antennas were described by Martin DKZB at: https://www.QSL.net/DK7ZB/start1.htm
For the 10m band, it is possible to modify a 3-element yagi to 50 ohms with a betamatch and a 2.4m boom, which can be purchased relatively cheaply. Its impedance is about 30 ohms and can be adjusted to suitable by simply modifying the lengths of the elements. PSV. Dva roky som túto anténu používal s vynikajúcimi výsledkami.
Konštrukčne jednoduchá je aj HB9CV, ľudovo nazývaná “hábéčko”. An excellent description of the genesis of this antenna appeared some time ago on the OK2KKW website. https://www.ok2kkw.com/HB9CV/hb9cv_1969.htm . Opinions on HB9CV are varied - some radio amateurs had problems with it. HB9CV is particularly interesting in terms of high gain and large F/B ratio.
Moxon beam has an advantage over these antennas in smaller dimensions, but requires thoughtful mechanical construction. It is more likely to be used by low band contesters, as it can be realized as a fixed wire directional antenna with electrically switchable radiation direction.
Spiderbeam is a multi-band multi-element antenna, which excels with a number of good properties. Due to its low transport weight and dimensions when disassembled, it has immediately found favor in expedition operations, but it is also an excellent antenna for home use. Home construction is also possible, but its commercial price is not so high that it would be worthwhile to realize it 'on the knee'.
Trapovaný tribander je veľmi populárna anténa and many manufacturers include it in their range. Home construction is very demanding, as the tribander is electrically and mechanically quite a complex antenna.
Rotators are an expensive matter. The principle is very simple: a slow-speed motor with a gearbox. The problematic part is acquiring a suitable gearbox. Larger rotators are supplemented with an electromagnetic brake, which is a big problem when manufacturing 'on the knee'.
Surprisingly good results can be achieved with the AR-300XL rotator. The advantage is the very high-quality and sturdy materials from which the rotator is made. If we eliminate vertical loading and misalignment, the rotator can also turn a smaller HF antenna. This requires the use of two bearings and a lot of thought, but it is possible. Some pieces have problems with azimuth indication; it is ideal to use independent rotation indication.
Professional lattice masts are not available for novice Hams. On a flat roof, we can easily realize a mast - a tripod. We secure the structure to weights that we make by pouring concrete into old tires. Be careful with the weight so that the roof can support it.
A fixed mast with a height of about 10m can be made by connecting two long scaffolding pipes. We will dig the foundations into the ground to a depth of at least 1m, into which we will install the first scaffolding pipe. After 120 degrees, about 10m from the base of the mast, we will dig a trio of foundations for anchoring. This can go into the ground if we install short scaffolding pipes and secure the anchoring up, it won't bother anyone. After the foundations have set, call your friends, make a low scaffold, and prepare the second pipe with the antenna. We lifted such a system with three people without problems, but it would probably go even better with five.even better.
The construction of masts is a challenging thing; it's better to over-dimension everything than to wipe away tears later. Don't forget about grounding.
Simple VHF antennas
To embark on VHF to contest with antennas like ¼, ½, Slim-Jim and similar ones is pure nonsense. The four most commonly used types of antennas are: yagi, quad, quagi a paraboly.
Yagi antény are popular for their good electrical parameters and simple mechanical construction. Thanks to this property, they can be made detachable, which allows transport to temporary stations.
Here too, the fashion wave works - very popular are yagi DK7ZB, ktoré sa presadzujú na úkor starších F9FT, DL6WU, DJ9BV, PA0MS, Y23RD a iných. Pri dodržaní konštrukčného postupu antény pracujú vynikajúco. Najnáročnejšie je zhotovenie DK7ZB matchu z koaxiálnych káblov. Na trhu je množstvo káblov, ktoré nie sú na tento účel práve najvhodnejšie, oplatí sa prejsť aj pár obchodov a nájsť najlepší z hľadiska spájkovateľnosti a ohybnosti. Verzie 50 a 28 ohm DK7ZB antén sú vhodné aj pre začiatočníkov, po 12,5 ohmových veľmi nesiahajte – sú veľmi ostré a kritické na okolité prostredie.
Quady sa napriek vyniakjúcim elektrickým vlasnostiam veľmi nerozšírili. Je to dané ich mechanickou zložitosťou. Osvedčenou anténou je DL7KM “osmička, dvojitý quad”. The antenna is relatively broadband, has an impedance of around 50 ohms and a gain of 7-8 dBd. At 2m, the 7-element quad according to GW4CQT was popular at one time.
Quagi is a hybrid antenna that results from combining elements from a yagi (directors) and a quad (radiator and reflector). The advantage is a higher gain than that of a yagi of the same length and a higher impedance at the feed point with only slightly more complex mechanical construction than a pure yagi. Such an antenna was used, for example, by W5UN. .
Parabolic antennas dominate higher VHF bands.. Zhotovenie mnohoprvkovej yagi s rovnakým ziskom ako má parabola je veľmi náročné na presnosť. V prípade použtia továrenskej paraboly, resp. parabolickej výseče (napr. SAT, WIFI) postačuje zhotoviť vhodný ožarovač a nastaviť anténu. Osvedčenými ožarovačmi sú konštrukcie podľa DB6NT, DL4MEA a iné.
Due to the much lower weight, dimensions, and wind resistance, VHF antennas put less strain on the mast and rotor. Smaller antennas can also be rotated manually, which is very operational.
Since the radiation pattern (especially of longer) VHF antennas is narrower, it is worth spending time on precise azimuth adjustment. Due to surrounding objects, such as the mast, the mechanical axis of the antenna may not align. For this purpose, it is possible to directly use signals from the band, beacons, or other stations to calibrate the antenna rotation.
Coaxial cables and connectors must be perfect.. Mnoho začínajúcich VKV amatérov túto skutočnosť podceňuje so slovami “však to chodí”. Nevhodný je koaxiálny kábel RG-58. Ak potrebujete tenký kábel, napríklad kvôli váhe, inšpirujte sa koaxiálmi používanými vo WIFI technike. Z konektorov preferujte radšej dlhšie verzie, ktoré lepšie zachytávajú ťah kábla. Radšej kúpte kvalitný konektor za stopäťdesiat korún ako päť mizerných po tridsať…
Množstvo zo spomínaných antén nájdete aj tu – na www.CQ.sk.
Glossary
impedance at the feed point - it is the impedance at the antenna radiator without any matching circuit.
half-wave dipole - a simple resonant antenna balun - impedance transformer. transformátor, ktorý navyše zabezpečuje prechod medzi symetrickou a neysmetrickou záťažou
trap - an LC element added to the antenna for the purpose of electrically lengthening or shortening a component, thereby achieving resonance.
tuner - an antenna matching element that ensures impedance transformation.
tribander - an antenna capable of operating on three bands.
rotator - a device for rotating the antenna.
boom - the supporting part of the antenna to which individual elements are attached.
lattice mast - a mast in the shape of a pyramid, very sturdy.
Slim-Jim - a simple VHF antenna.
Match - antenna matching circuit.
Antenna radiation pattern - usually a graphical representation of the directional distribution of energy radiated by the antenna.
Next time: how to make contesting easier