VHF-UHF portable Yagi-Uda and design notes XE1MEX
When I added links about antennas to www.cq.sk on one of the last pages, which I also visited was the Alexa XE1MEX website. I found there an interesting antenna suitable for satellite operation on bands 144 a 432 MHz. I liked its construction, so I asked Alex for permission to translate and publish it. I immediately got a positive answer. I found out too, that this description has already been translated into French, Polish and Turkish, while Alex has an English and Spanish version on the site… In addition, he writes, that he has already confirmed 51 DXCC via satellites and is also very active on AO-40. He would be delighted to QSO with OM, because this prefix is still missing in his collection….
Introduction
Because in my city it was very difficult to buy a factory VHF-UHF portable antenna, so I decided to make it from old HF and VHF antennas. My personal commitment was to make it to my vacation in Cancun (2.-8.may 1999), so that I can broadcast from the EL61 square via the AO-27 satellite. The antenna worked perfectly and I was able to make a large number of connections. I have been using it at home since then (EL08MU) and always, when I can broadcast from another square. In year 1999 they were: EK09, EL00 a EL61; in 2000: EL60 a EL61; in 2001: EL61, EL50, EL51, EK06, EK07 to DK96. I have successfully used this antenna for satellite connections AO-27, SO-35 (* t.no. is no longer there), UO-14, FO-20, FO-29 a AO-10. See the latest photos and notes in the article!
Software
developed a program in GW Basic for the calculation of a double Yagi-Uda VHF and UHF antenna Guenter Hoch, DL6WU. You can download it from Alex's site (cca.80kB): download Yagi-Uda program from DL6WU. In case, that a request for a password or login would occur during the download, write to Alex, will send it to you by e-mail. Sometimes it happens, that the server rejects the request to download the file.
Follow these instructions when using the program:
1. Unzip the antenne.zip file to a new directory on your PC
2. Try running the Antdl6wu.bas file with Windows Explorer
3. If you see a dialog box with a question, what program to use to run that file, then select “Other (Other)” and highlight Gwbasic.exe, which is in the directory, which you created in the first step
4. The program will run in Windows 95, 98, 2000, XP or NT in a separate window. So answer Y to the question (Yes) and press Enter – the program will start.
Construction details
let's assume, that you managed to download and run the program. Considering the specific requirements and the available material, I achieved the following results based on the calculation:
– medium frequency VHF: 145,850 MHz
– medium frequency UHF: 436,800 MHz
– number of elements: 8 by UHF (profit 10,5 dBd) a 4 and VHF (profit 6,46 dBd)
– boom diameter: 22 mm
– feature average and gammamatch: 9 mm
– lengths of the elements of the VHF part: R=1017, D=972, D1=917, D2=906
– distances between the elements of the VHF part: R a D=380, D a D1=162, D1 a D2=370
– lengths of UHF part elements: R=349, D=325, D1=303, D2=298, D3=292, D4=287, D5=285, D6=282
– distances between elements of the UHF part: R a D=127, D a D1=54, D1 a D2=123, D2 a D3=148, D3 a D4=173, D4 a D5=193, D5 a D6=207
– reflectors are mounted 15 mm (VHF) a 25 mm (UHF) from Wednesday spotlight to food boom (over the boom). (thanks to XE1YJS for the edit! – 2.February 2002)
NOTE: all dimensions are in millimeters, all elements are made of aluminum tubes, R is a reflector, D is the emitter, D1 to D6 are directors, element distances are from element center to element center, elements are assembled over the boom – (not through the boom), whereas they are not isolated from the boom.
As a holder, I slid a Teflon rod into the boom (length 430 mm, 100 mm v boom-e). However, you can use any non-conductive material.
I used aluminum tubes of these diameters, because I had them at home, but I strongly recommend using thinner tubes (possibly sticks), so that the antenna is not so heavy… you will definitely remember it during longer sessions. If you do so, do not forget to recalculate the dimensions of the antenna.
Gamma match
let's take a look at “heavy” section – adaptation of the coaxial cable to the power point of the emitters. Because this is a portable antenna and I'm using it near the transceiver, so I ignored the losses of the inferior RG-58 A/U and used it at length 1200 mm between the device connector and each emitter.
Gamma adjustment is seamless and well-tried. I have always had excellent results with it, maybe because, because I don't use any other type of coupling capacitance than a bare piece of RG-8, RG-213 or RG-214 inserted into a small piece of aluminum pipe. By the term bare piece, I mean a piece of coaxial cable without an outer plastic jacket and braid. It forms a connection between the sleeve and one arm of the emitter. I use the TT3G50HP lightning arrester as a rough protection and then a relay antenna switch, that these pictures will tell you more than a thousand words….
Warning: (18.February 2001) most frequently asked questions from friends, who decided to make this antenna are related to gammamatch. You've asked this so many times… maybe this drawing will help you.
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– VHF: Al tube gamma is long 150 mm, the total length of the bare coax is 230 mm, whereas 68 mm of it is in an aluminum tube. Al clutch (short circuit between gamma “with a stick” and emitter) is placed 310 mm from the center of the boom, distance between gamma “with a stick” and the radiant is 30 mm (from Wednesday to Wednesday)
– UHF: Al tube gamma has 50 mm, the total length of the bare coax is 68 mm, whereas 20 mm of it is in an aluminum tube. Al clutch is remote 84 mm from the center of the boom, distance between gamma “with a stick” and the radiant is 20 mm (from Wednesday to Wednesday)
– Many thanks to Marcin Koron SP8UFX for his comments, which helped fix multiple dimensions of the UHF gamma match! (15.may 2001)
In case, that you want to gently reach the minimum PSV and you have a good one PSV meter, look for it with at least a bare piece of coax inserted or extended and/or move the shorting connector back and forth.
Results
good news after a lot of effort…if you build this antenna, I can guarantee you, that PSV will be lower than 1,3:1 on the middle frequencies of both bands and will not be worse than 2:1 on its borders.
I could not measure the gain of the antenna, I believe though, that it is close to the theoretical one – in any case, just point to AO-27, SO-35 (item no. not anymore), UO-14, FO-20, FO-29 or AO-10 and I'm sure, that you will be satisfied.
OK, as you can see, I am not writing anything about the duplexer. It is because, because I use two devices – one on 2 m and the other on 70 cm. But I'm going to build it soon, if it works as I imagine, so of course I will describe it.
It also works with FC-20, that this antenna will bring you as much joy as it does me… 73's from XE1MEX….Alex
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UPDATE
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NEW!…. Same antenna, I have the one I described installed on the top of the mast, where it replaced the helical antenna, which I repair. The antenna has a fixed elevation 30 degrees and is rotated by a rotator. The results are quite good – you can also try it, just for fun, or because of that, to have cheap access to the AO-27 satellites, SO-35*, UO-14, FO-20 and FO-29!! Excuse me, I forgot to say, that I still haven't built one yet duplexer – I bought a Diamond MX-72D, which is located below the rotator, where a plastic bottle protects it against the effects of the weather. This is how I have both yagins powered by one coaxial cable. Check it out in the pictures.
EXTRA!!…. The fourth of June 2002 I established the first connections via FO-20 and FO-29 with this antenna! The homemade yagi also works great for receiving all digital satellites. One of you recorded an ISS crew, that work through five (* only four more) of satellites with a homemade portable yagi is not a bad result… naturally, it is possible to increase the number of elements and thus achieve a greater profit based on the calculation by the program.
NEWS FLASH!!!…. The twentieth of August 2000 I established the first connections via AO-10 ONLY with this antenna – 16 I did not use an element horizontal yagi! Another milestone of this antenna. Although the distance to the satellite was “small” (okolo 8000 kilometers), it was an incredible experience to communicate through the AO-10 only with 20 watts and 8 elements on the UHF uplink and 4 elements on the VHF downlink… Tranceiver bol ICOM IC-706MKIIG. What else can I say about a homemade cross yagi?… UI-View displays the contents of packets below the map with a text report…it is cheap, portable, easy to make, and it is possible to work with it at least through 6 satellites. I'm sure too, that it can also be used for satellites operating in digital modes, but at the moment I cannot confirm it.
DUPLEXER…. I still haven't made it yet, but if you are looking for interesting and good information about him, I recommend Lee Devlin's website, K0LEE, which includes a Microduplexer tutorial by Chuck Duey, KI0AG.
Just for information: during the year 200 I had 554 of successful connections with this antenna via AO-10 satellites, UO-14, AO-27, FO-20, FO-29 a SO-35.
Finally, I want to thank you for your comments, notes and words of encouragement to the following amateurs, who built this cross antenna and use it successfully…thanks to all of you!!: SP8UFX, XE2ARF, 9Z4DZ, ZL2GVA, ZZ2UHT, YD3RCJ, KF6WCH, KF6PHX, DF8GH, LET'S GO, KK5UFO a IZ5DWF. Thanks to everyone too, who are not named, but they also built it on other bands based on this article.
I especially want to thank Mr. Guenter Hoch, DL6WU, for his attention, persistence and useful information sent by email.
xe1mex@yahoo.com
The original article with full-size images and a possible further update can be found at: http://xe1mex.gq.nu/antenas/yagi.html
Slovak translation by Viliam OM3-0122
