BASIC YAGI ANTENNA DESIGN FOR THE EXPERIMENTER This article is not designed to give you construction details for building a Yagi. It is designed to give you a better basic understanding of how the Yagi is designed and the basic functions of each of its parts. They discovered that by adding "elements"of various lengths and spacings in front of and behind a dipole antenna that the performance and effectiveness of the dipole could be greatly increased and the pattern of the dipole rf energy could be "beamed" or focused in one direction, with the resulting "effect" of making it appear that the transmitter was running lots more power than it actually was, yielding much stronger signals both on receive and transmit! DESIGNING AND BUILDING A YAGI FROM SCRATCH USING THE COMPUTER! W7RAI has a very nice DOS based Yagi design program that can be downloaded for FREE! Thanks for http://www.hamuniverse.com/yagibasics.html
Helpful non-technical, no theory user information for
Yagi Antenna Design and How to Understand basic Yagi's
Condensed and re-edited from various sources
GENERAL DESCRIPTION OF A YAGI
The word "Yagi" is used to describe a type of antenna and is credited to very famous Japanese antenna experts by the names of Yagi and Uda! Most hams refer to this type of antenna as the "Yagi" rather than use both men's names.
The Yagi antenna's overall basic design consists of a "resonant" fed dipole (the fed dipole is the driven element and in the picture above and the second from the left side ), with one or more parasitic elements.
These parasitic elements are called the "reflector"and the "directors."
The reflector is on the far left in the picture above and the directors are all of the elements starting from the third element from the left and continuing to the right side of the picture.
The horizontal section between all of the elements in the Yagi is called the boom.
From experimentation, they determined that the "effect" of their designs created much more "powerful" antennas compared to the standard dipole by just adding a few more elements to it.
They also learned that by changing the space between the elements, and the element lengths, that they could "tune" it to get various results depending on what they wanted it to do. They found that they could change the forward "gain" of it and also that they could change the way it performed in other aspects.
THE ELEMENTS OF A YAGI
THE DRIVEN ELEMENT
The driven element of a Yagi is the feed point where the feed line is attached from the transmitter to the Yagi to perform the transfer of power from the transmitter to the antenna.
A dipole driven element will be "resonant" when its electrical length is 1/2 of the wavelength of the frequency applied to its feed point.
The feed point in the picture above is on the center of the driven element.
THE DIRECTOR
The director/s is the shortest of the parasitic elements and this end of the Yagi is aimed at the receiving station. It is resonant slightly higher in frequency than the driven element, and its length will be about 5% shorter, progressively than the driven element. The director/s length/s can vary, depending upon the director spacing, the number of directors used in the antenna, the desired pattern, pattern bandwidth and element diameter. The number of directors that can be used are determined by the physical size (length) of the supporting boom needed by your design.
The director/s are used to provide the antenna with directional pattern and gain.
The amount of gain is directly proportional to the length of the antenna array and not by the number of directors used. The spacing of the directors can range from .1 wavelength to .5 wavelength or more and will depend largely upon the design specifications of the antenna.
THE REFLECTOR
The reflector is the element that is placed at the rear of the driven element (The dipole). It's resonant frequency is lower, and its length is approximately 5% longer than the driven element. It's length will vary depending on the spacing and the element diameter. The spacing of the reflector will be between .1 wavelength and .25 wavelength. It's spacing will depend upon the gain, bandwidth, F/B ratio, and sidelobe pattern requirements of the final antenna design.
BANDWIDTH AND IMPEDANCE
The impedance of an element is its value of pure resistance at the feed point plus any reactance (capacitive or inductive) that is present at that feed point. Of primary importance here is the impedance of the driven element, the point on the antenna where the transfer of rf from the feedline takes place.
Maximum energy transfer of rf at the design frequency occurs when the impedance of the feed point is equal to the impedance of the feedline. In most antenna designs, the feedline impedance will be 50 ohms, but usually the feed point impedance of the Yagi is rarely 50 ohms. In most cases it can vary from approximately 40 ohms to around 10 ohms, depending upon the number of elements, their spacing and the antenna's pattern bandwidth. If the feedline impedance does not equal the feed point impedance, the driven element cannot transfer the rf energy effectively from the transmitter, thus reflecting it back to the feedline resulting in a Standing Wave Ratio. Because of this, impedance matching devices are highly recommended for getting the best antenna performance.
The impedance bandwidth of the driven element is the range of frequencies above and below the center design frequency of the antenna that the driven element's feed point will accept maximum power (rf), from the feedline.
The design goal is to have the reactance at the center design frequency of the Yagi = (0),,, (j + 0).
The impedance matching device will now operate at it's optimum bandwidth. Wide element spacing, large element diameter, wide pattern bandwidth, and low "Q" matching systems will all add to a wider impedance bandwidth.
ABOUT ANTENNA PATTERNS
The antenna's radiation pattern or polar plot as it is sometimes called plays a major role in the overall performance of the Yagi antenna.
The directional gain, front-to-back ratio, beamwidth, and unwanted (or wanted) sidelobes combine to form the overall radiation pattern. The antenna's radiation pattern bandwidth is the range of frequencies above and below the design frequency in which the pattern remains consistent.
The amount of variation from the antenna's design specification goals that can be tolerated is subjective, and limits put into the design are mainly a matter of choice of the designer. "In other words.....trade offs".
Equal spaced, equal length directors may give higher gain at a particular frequency, but the bandwidth is more narrow and larger sidelobe levels are created.
Wide spacing will increase the bandwidth, but the sidelobes become large.
By varying both the spacing and director lengths the pattern and the pattern bandwidth may be more controlled.
More directors within a given boom length won't increase the gain by any great amount, but will give you better control of the antenna's pattern over a wider range of frequencies in the band of design.
If you reduce the length of each succeeding director by a set factor (%), AND increase the spacing of each succeeding director by another factor, a very clean pattern with good pattern bandwidth can be obtained.
The TRADE OFF......will be a small loss in the optimum forward gain (10% to 15%).
In a nutshell......when you make a change to one part of the antenna, this changes the performance of another part.....all changes interact with each other and the final performance!
GAIN vs FRONT-TO-BACK RATIO
With highest forward gain design, the main lobe becomes narrower in both the elevation and azimuth planes, and a backlobe is always present. When you design "out" the backlobe, the pattern gets wider and the forward gain goes down. In some cases, the sidelobes become quite large.
A WELL FED YAGI IS A HAPPY YAGI!
There are many ways to feed the Yagi, but they can be condensed into two main categories:
The balanced feed and unbalanced feed.
The Balanced feed system:
This may give a broader impedance bandwidth, but the main problem is that the driven element must in most cases be split in the center and insulated from the boom. Construction considerations aside, it is the better of the feed systems. Meeting the requirements of a balanced matching system is usually the main problem, but there are many methods available.
One method is to not split the driven element and use a "T" match, which can be described as two gamma matches on each side of the center of the element, fed with a 1:1 balun at the center.
The main drawback is that it's difficult to adjust.
The Unbalanced feed system:
Another method (for low impedance feed points) uses a split element insulated from the boom, and is fed with a "down-step 4:1 balun" made by combining two 1/4 wavelength sections of coaxial feedline in parallel, attaching an equal length of insulated wire to the outside of these sections, and connecting it to the center conductors at the feed point end and to the shields at the feed-line end. The impedance of this type of "balun" should be at or near the mid-point value between the feed point impedance and the feedline impedance.
For example, two 75 ohm sections paralleled will equal 37.5 ohms and will match a 25 ohm feed point to a 50 ohm feedline with a 1.0 to 1 SWR.
The most common method in use by hams today is the gamma match. It will provide an easy and sure method of matching to the feed point without any loss of bandwidth.
It will save you all that tedious math and the frustrations involved in designing a Yagi.
It will "design" a multielement Yagi for frequencies up to 999mhz. You simply download it from the link below, install it and run. You can tweak many of the variables in it to design a Yagi that will perform well for you. There is also a program within it that will design a gamma match.
Run QYUTIL.EXE in the QY4 PROGRAM from WA7RAI
for the gamma match construction details.
DOWNLOAD THE QY4 ANTENNA DESIGN PROGRAM HERE
SEE A 6 ELEMENT 2 METER SSB (144.250) DESIGN HERE
Further information on antenna design and feed systems, see The Radio Amateurs Handbook, The ARRL Antenna Handbook, Dr. J.L. Lawson's Yagi Antenna Design (ARRL), or Bill Orr's Radio Engineer's Handbook, to name only a few.
Thanks to all who make Ham Radio antenna design and experimentation a fantastic sub-hobby to Amateur Radio.
Sunday, October 25, 2009
BASIC YAGI ANTENNA
ShortWave Listener ( SWL )
Many radio amateurs started their hobby listing to shortwave radio. Starting with radio broadcasts from distant countries, they become interested in receiving weak or distorted radio signals on congested frequency bands. A very popular aspect of his hobby is to monitor radio communications on the many frequency bands, allocated by internation agreement to amateur radio. Receiving other kinds of radio transmission, like standard time signals, may sometimes be very interesting. The reception of signals from radio beacons can provide usefull information about the propagation of radio waves. The SWL very often builds his own equipment, from antennas to receivers and signal processors. And with the availability of personal computers, other communication modes, such as weathermaps, radio telex bulletins, slowscan television have become increasingly popular.What is a ShortWave Listener ( SWL )
Monday, August 24, 2009
Radio amatur
Radio amatur merupakan salah satu daripada jenis komunikasi yang menggunakan peralatan radio dan elektronik. Penggunaan radio amatur di dalam bidang komunikasi amatlah luas kerana dapat digunakan bagi menghubungkan seorang yang berada samada di dalam kawasan atau ke seluruh dunia dengan menggunakan set radio amatur yang tertentu pada frekuensi yang tertentu.
Seperti yang diketahui umum bahawa komunikasi menggunakan radio amatur hanyalah sekadar bercakap sahaja, tetapi apa yang berlaku kini dengan perkembangan teknologi komunikasi yang begitu pantas, sistem perhubungan yang dahulunya menggunakan sistem anolog kini telah bertukar kepada sistem digital yang membenarkan kita bukan hanya dapat bercakap sahaja malahan dapat melihat seperti sebuah televisyen yang boleh dipancarkan hampir ke sebahagian besar dunia. Kebanyakan daripada pengguna radio amatur memancarkan signal mereka melalui satelit yang berada pada orbit di dunia ataupun menggunakan bulan sebagai pemantul isyarat bagi memancarkan isyarat yang dipancarkan oleh set mereka.
Terdapat juga sebahagian daripada mereka berkomunikasi menggunakan "kod Morse". Pengendali radio amatur merupakan sebahagian dari penduduk dunia yang mempunyai syarat penggilannya (call sign) sendiri yang merupakan pasport untuk ke seluruh dunia melalui gelombang udara. Sempadan negara, ideologi politik, warna kulit, pangkat atau kedudukan seseorang adalah sama sekali tiada di dalam dunia radio amatur, namun masih terdapat sebahagian kecil lagi negara di dalam dunia ini masih tidak membenarkan penggunaannya di negara sebagai sebahagian dari aktiviti pada masa terluang.
Keseronokan menggunakan perhubungan radio amatur oleh pengendali-pengendalinya ke negara lain menyebabkan sesetengah darinya menghasilkan ikatan persahabatan yang berlarutan yang pada mulanya perjalanan yang jauh menggunakan kapal terbang untuk menemui mereka. Mereka yang dihubungi melalui radio sahaja bagi mengeratkan lagi persahabatan yang sedia ada sebelumnya.
Untuk semua
Radio amatur adalah untuk semua orang tanpa mengira jantina, umur, pangkat, agama, bangsa atau keupayaan. Sebagai seorang pengendali radio amatur, mereka akan dapat sesuatu yang menyeronokan dengan suatu sentuhan yang agung bagi kepuasan diri mereka. Di Malaysia juga sesiapa sahaja boleh menjadi ahli dan berhubung ke seluruh dunia. Radio amatur akan menyediakan suatu pengalaman yang amat baik untuk menjerumuskan diri kita ke dalam bidang elektronik yang semakin disertai ramai.
Dari sini dapatlah diperhatikan bahawa radio amatur boleh disertai oleh sesiapa sahaja dari golongan bawahan hingga ke peringkat atasan seperti Raja Hussein dari Jordan, Raja Juan Carlos dari Sepanyol, Senator Barry Goldwater dan ramai lagi yang menjadi sebahagian dari masyarakat radio amatur. 9M2TR ialah Y.B.M Tunku Abdul Rahman ibni Al-Marhum Sultan Sir Ismail Al-Khalidi (25 November 1933–12 July 1989) yang juga merupakan bekas Tunku Mahkota Johor dan adik bongsu kepada Sultan Mahmud Iskandar Al-Haj ibni Al-Marhum Sultan Sir Ismail Al-Khalidi (Sultan Johor sekarang).
Cara beroperasi
Komunikasi melalui radio amatur tidak seperti penggunaan telefon bimbit kerana liputannya tidak terbatas kepada kawasan berpenduduk sahaja. Keupayaan radio amatur bergantung kepada antenanya dan juga jaluran (band) yang digunakan. Semakin tinggi antena (atau semakin banyak elemen sesebuah antena itu, semakin baik keupayaannya).
Di dalam keadaan darurat seperti bencana alam, peranan radio amatur amat menonjol di dalam memberikan kemudahan perhubungan. Contoh aplikasi radio amatur yang digunakan ketika bencana di Malaysia ialah ketika tragedi Highland Towers pada tanggal 11 Disember 1993 yang telah mengorbankan 48 nyawa, apabila Malaysian Amateur Radio Transmitters' Society (MARTS) tampil memberikan kemudahan perhubungan komunikasi di antara lokasi runtuhan dengan hospital. Pada 6 Disember 2008 pula, Malaysian Amateur Radio Emergency Service Society (MARES) telah menubuhkan komunikasi kecemasan di Bukit Antarabangsa, Ampang untuk membantu dalam memberi liputan dan juga bantuan dari segi komunikasi kepada pihak berkuasa yang menjalankan kerja-kerja menyelamat mangsa kejadian tanah runtuh.
Secara asasnya, terdapat 2 jenis komunikasi di dalam radio amatur iaitu secara simpleks dan satu lagi melalui pancar ulang. Simpleks (simplex) merupakan kaedah perhubungan radio secara point to point. Seakan menggunakan radio FRS seperti Motorola Talkabout. Pancar ulang atau repeater pula merupakan perhubungan melalui sejenis peranti yang menerima (RX) dan menghantar (TX) kembali audio kita. Pancar ulang lazimnya terletak di kawasan tinggi seperti di gunung/bukit bagi membolehkan ia menerima dan menghantar semula audio ke tempat yang lain pada jarak yang lebih jauh.
Pancar ulang penting kerana ada kalanya komunikasi agak sukar kerana terlindung oleh halangan seperti struktur binaan manusia seperti bangunan mahupun muka alam seperti bukit dan gunung. Oleh yang demikian, bagi membolehkan audio disampaikan ke kawasan yang terlindung, pancar ulang diperlukan. Di Malaysia hampir kesemua pancar ulang dimiliki oleh persatuan radio amatur seperti MARTS, MARES, ASTRA, JASRA dan lain-lain lagi yang boleh dimanfatkan oleh ahlinya untuk berkomunikasi dengan rakan lain samada secara lokal mahupun transnasional (seluruh negara).
Undang-undang
Lesen radio amatur di negara ini terbahagi kepada 2 kelas iaitu A dan B. Lesen B merupakan lesen asas yang dikeluarkan kepada calon yang lulus RAE. Lesen B membolehkan operator radio amatur mengendalikan radio pada julat dan kuasa pancaran (watt) yang lebih rendah berbanding pemegang lesen kelas A. Pemegang lesen kelas B akan mendapat callsign yang bermula dengan 9W2 atau disebut sebagai Nine-Whiskey-Two manakala pemegang lesen kelas A disebut sebagai 9M2 atau Nine-Mike-Two. Callsign tersebut adalah unik bagi setiap pemegangnya dan digunapakai untuk berhubung ke seluruh dunia.
Mereka yang ingin mendapatkan lesen kelas A, perlu terlebih dahulu memiliki lesen kelas B untuk sekurang-kurangnya 1 tahun sebelum boleh memohon untuk menduduki ujian CW (continous wave) atau Kod Morse. Hanya mereka yang lulus sahaja akan diberikan lesen kelas A dan boleh mengendalikan perkakasan radio berkeupayaan tinggi selain boleh berhubung menggunakan Kod Morse hanya dengan menggunakan bateri berkuasa 9 volt.
Di Malaysia, perkhidmatan radio amatur dipantau oleh Suruhanjaya Komunikasi dan Multimedia (MCMC). Seseorang yang ingin menjadi mengoperasikan perkakasan radio komunikasi amatur perlu terlebih dahulu menduduki Peperiksaan Radio Amatur atau RAE (Radio Amateur Examination) yang dikelolakan oleh MCMC. Calon yang lulus akan dibenarkan untuk membuat permohonan untuk mengoperasikan perkakasan radio amatur dan diberikan callsign atau tanda pengenalan untuk berkomunikasi. Hanya selepas memperolehi AA atau Apparatus Assignment (penguntukan radas/lesen) dari MCMC, seseorang boleh mula ber"QSO" atau berbual di dalam jaluran.
Setiap negara mempunyai badan yang bertanggungjawab memantau semua aktiviti yang berkaitan dengan radio amatur sebagaimana MCMC untuk Malaysia. Badan ini diikhtiraf oleh ITU International Telecommunication Union iaitu badan yang menyelia dan memantau aktiviti berkenaan telekomunikasi pada peringkat antarabangsa. Peruntukan callsign untuk sesuatu negara adalah dibuat di peringkat ITU. Badan khas yang memantau operasi radio amatur di peringkat ITU adalah IARU International Amateur Radio Union. Setiap negara mempunyai hanya satu persatuan radio amatur yang diikhtiraf oleh IARU. Untuk Malaysia, persatuan yang diikhtiraf oleh IARU adalah MARTS. Walaupun begitu, persatuan-persatuan lain yang berasaskan lokaliti (negeri, daerah, institusi dan sebagainya) atau kumpulan minat (pacuan 4 roda, khidmat kecemasan, pengembaraan dan sebagainya) bebas ditubuhkan dan beroperasi di Malaysia.
Persatuan-persatuan Radio Amatur di Malaysia
Malaysian Amateur Radio Transmitters' Society (MARTS) www.marts.org.my
Persatuan Radio Amatur Melayu Utara Malaysia (ASTRA) http://www.astra.org.my/
Malaysian Amateur Radio Emergency Service Society (MARES) www.mares.org.my
Persatuan Radio Amatur Pahang (PERAMAH) http://www.peramah.org.my/
Kelab Radio Amator Negeri Sembilan (NESRAC) http://www.nesrac.org/
Jalur Selatan Radio Amatur Johor (JASRA) http://www.jasra.org.my/
Persatuan Radio Amatur Perak (PARTS) http://www.parts.org.my/
Kelab Radio Amatur dan Rekreasi Terengganu (PEMANCAR) http://www.pemancar.org/
Kelab Radio Amatur TIME (TIME ARC) www.timearc.org
Kelab Radio Amatur PKG Segamat http://radioamaturpkgsegamat.blogspot.com/
Portal Radio Amatur Alor Setar (ASHAMRADIO) http://www.ashamradio.com
Amateur Radio Kota Bharu (ARKB) http://www.arkb.org.my
Rakan Radio Amatur Sg. Petani http://www.sphamradio.com
Persatuan Pemancar Radio dan Komunikasi Dua Hala Melaka (MERACC) http://www.meracc.ultramaya.com
Kinabalu Amateur Radio Transmitting Soceity (KARTS) http://www.9m6ktc.net
PERSATUAN RADIO AMATUR MELAKA (PERAKAM) http://perakam.blogspot.com
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