We start with contesting - the third part
Good antennas
The beginning radio amateur will find it difficult to orientate himself in various antenna designs. Antenna books and the internet are full of various constructions. The result sheets are a good guide for which antenna to choose, in which the type of antenna is indicated.
If we don't buy a finished antenna, we need to know when designing, which dimension or material has a significant effect on the resulting properties of the antenna. Personally, I prefer years-proven antenna designs or direct coaxial antenna antennas because of:
- each matching circuit has certain losses
- due to the absence of measuring instruments, it is easier to tune one thing (antenna) like two things (adapter and antenna)
- impedance antennas 50 ohm at the supply point is more wideband than the same type of antennas with lower impedance and matching circuit
- impedance antennas 50 ohms at the power point are much less sensitive to surrounding antennas and other objects
- simpler construction
- … However, the disadvantage is a slightly lower profit and worse F / B (penultimate) ratio
Simple HF antennas
A simple proven antenna is horizontal half - wave dipole. When powered in the middle, the impedance will be close 50 ohmom. Its value depends on the height above the ground and surrounding objects (buildings).
We calculate the length of the half-wave dipole: l = 150/f [m;MHz]
In practice, the length will be slightly shorter, which we will use in the final adjustment of the antenna in the given environment (we are shortening). End insulators can be purchased, resp. made of old coarse coaxial cable with teflon dielectric. The wire must be strong enough, to withstand the load.
Due to the fact, that the coaxial is an unbalanced feeder and the half-wave dipole fed in the middle is a symmetrical antenna, their connection should be solved by a balun 1:1. Proper construction of the balun requires suitable material and winding technique - if these conditions are not met, Wonderful article will not perform its function properly. We can also use commercially available baluns, do not use a balun at low power or portable antenna (not recommended).
In the higher bands, we can replace the balun with several turns of coaxial cable just below the antenna.
A popular shape is a dipole in the shape inverted V-eye. It requires only one high attachment point and part of the energy is radiated even with vertical polarization, which is advantageous for DX connections.
Multiband dipole antennas offer a compromise option to work on multiple bands. They are implemented with traps (e.g.. W3DZZ), tuned (e.g.. G5RV, Zepelin), multiple parallel emitters or other means of power supply (FD-4).
The vertical quarter-wave radiator is an excellent DX antenna. It requires a system of counterweights - radial. In the case of terrestrial (buried in the ground, or laid on the ground) applies, that the more and the longer - the better. Tens to hundreds of radials make a truly efficient system. The advantage is, that the radials are inconspicuous and do not have to have a resonant length.
Unlike raised radials, which must have a resonant length. However, their advantage is, that we can achieve high efficiency with one to four radials. The two easiest to realize are the two radials, which we first tune to the band as a dipole or inv.V without a vertical emitter (enough 2 - 3m above the ground). Then we add a quarter wave radiator and check the resonance and adjustment of the antenna. From a band of 40 m, we can advantageously use telescopic rods made of glass fibers, which makes the implementation of the antenna very simple.
An excellent DX antenna for the lower band is inverted L antenna. It's suitable there, where it is not possible to implement a full-height quarter-wave antenna. Description of such one- the viacpásmovej (160m, 80m a 40m) antennas can be found at www.160m.de .
Material: buy at local electrical stores, toroids Amidon at www.awas.sk or www.ges.cz , parts or entire antennas also at www.ok5im.com
"It simply came to our notice then?“, is a common question. These are mainly very short vertical antennas (height less than 0,1 wavelength in a given band) and various replacement antennas, for example, antennas on a balcony.
The requirement to work on multiple bands can be solved by a multi-band antenna on a common boom. However, in domestic conditions the most feasible directional antenna is a 2-element yagi. The material is relatively affordable and the production requires only common tools - a saw, drill, measuring tape, screwdrivers and a set of wrenches.
Such antennas were described by Martin DKZB at: http://www.dk7zb.fox28.de/start1.htm
For the 10m band it is possible to modify to 50ohm also a 3-element yagi with betamatch and boomo 2.4m, which can be bought relatively cheaply. Its impedance is about 30 ohms and by simply adjusting the lengths of the elements, it can be delivered to a suitable PSF. I have been using this antenna with excellent results for two years.
It is also structurally simple HB9CV, popularly called "hábéčko". An excellent description of the genesis of this antenna some time ago appeared on the OK2KKW website http://www.ok2kkw.com/hb9cv/hb9cv_1969.htm . However, opinions on HB9CV are different - some radio amateurs have 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, however, it requires a thoughtful mechanical design. Low band contestants will reach for it sooner, as it can be realized as a fixed wire guide with electrically switchable direction of radiation.
Spiderbeam is a multi - band multi - element antenna, while excelling in a number of good features. Due to the low transport weight and the dimensions in the disassembled state, it immediately became popular during the expeditionary operation., but it is also an excellent antenna for home conditions. Home construction is also possible, but its commercial price is not that high, to make it worthwhile to implement "on your knees".
Rotators are an expensive affair. The principle is very simple: engine with slow gear. The problem is to import a suitable gearbox. Larger rotators are equipped with an electromagnetic brake, which is a big problem in making "on your knees".
Surprisingly good results can be achieved with the AR-300XL rotator. The advantage is very high quality and strong materials, of which the rotator is made. If we eliminate vertical loading and misalignment, the rotator can also rotate a smaller HF antenna. It requires the use of two bearings and a lot of consideration, but it works. Some pieces have a problem with azimuth indication, it is ideal to use an independent rotation indication.
Professional lattice masts are not available for beginners HAM. On a flat roof, we can easily implement a mast - a tripod. We attach the structure to the loads, which we make by pouring concrete into old tires. Watch your weight, to make the roof last.
Fixed mast with a height of approx. 10m can be done by connecting two long scaffolding pipes. We dig the foundations into the ground to a depth of at least 1m, in which we install the first scaffolding tube. After 120 degrees about 10m from the base of the mast, we dig three foundations for anchoring. It can go down, if we install short scaffolding pipes and anchor the anchorage at the top, will not bother anyone. After solidifying the basics, call friends, make a low scaffold and prepare a second tube with an antenna. We lifted such a system three times without any problems, in the bottom, however, it would probably go even better.
Building masts is a difficult thing, it is better to oversize everything than to wipe away the tears. Don't forget to ground.
Simple VHF antennas
Embark on VHF to contest with antennas such as ¼, ½, Slim-Jim and the like is pure nonsense. The four types of antennas are the most commonly used: yagi, quad, quagi and parabolas.
Yagi antenna are popular for good electrical parameters and simple mechanical construction. Thanks to this feature, they can be implemented as detachable, which allows transport to a temporary site.
Fashion wave works here too - they are very popular yagi DK7ZB, which are gaining ground at the expense of older F9FT, DL6WU, DJ9BV, PA0MS, Y23RD and others. The antennas work excellent when the design procedure is followed. The most demanding is making a DK7ZB match from coaxial cables. There are a lot of cables on the market, which are not the most suitable for this purpose, it pays to go through a few stores and find the best in terms of solderability and flexibility. Versions 50 a 28 ohm DK7ZB antennas are also suitable for beginners, po 12,5 ohmic do not touch much - they are very sharp and critical to the environment.
Quagi is a hybrid antenna, which is created by a combination of elements from yagi (direktorov) the quad (radiator and reflector). The advantage is higher gain than yagi of the same length and higher impedance at the supply point with only a slightly more complex mechanical construction of pure yagi. Such an antenna was used, for example, by W5UN http://web.wt.net/~w5un/w5unqu97.htm
Due to the much lower weight, the size and weight or wind resistance of the VHF antenna place less strain on the mast and rotator. Smaller antennas can also be rotated manually, which is very operational.
Since the radiation characteristics (especially longer ones) VHF antennas are narrower, it also pays to devote time to the exact adjustment of aziumut. Due to the surrounding objects, for example, the mast does not have to match the mechanical axis of the antenna. It is possible to use signals from the band directly for this purpose, beacons or other stations and the antenna rotation to be calibrated.
Coaxial cables and connectors must be perfect. Many beginning VHF amateurs underestimate this fact with the words "but it works". The RG-58 coaxial cable is not suitable. If you need a thin cable, for example, due to weight, get inspired by coaxials used in WIFI technology. Of the connectors, prefer longer versions, which better capture cable tension. You'd better buy a quality connector for one hundred and fifty crowns than five lousy ones for thirty…
You can also find many of the mentioned antennas here – at www.cq.sk..
Glossary
impedance at the supply point - this is the impedance at the antenna radiator without any matching circuit
half - wave dipole - simple resonant balun antenna - impedance transformer, which, in addition, ensures the transition between symmetrical and non-symmetrical loads
trap - LC member inserted into the antenna for the purpose of electrical extension or shortening of the element, thus achieving resonance
tuner - antenna tuner, which provides impedance transmission
tribander - antenna capable of operating on three bands
rotator - device for rotating the antenna
boom - the supporting part of the antenna to which the individual elements are attached
lattice mast - a pole in the shape of a pyramid, very strong
Slim-Jim - simple VHF antenna
Match - antenna matching circuit
Antenna radiation characteristics - mostly a graphical representation of the directional distribution of the radiated energy by the antenna
Next time: making contesting easier
