Radio Havana Cuba Dxers Unlimited Dxers Unlimited’s weekend edition for May 12-13 2007 By Arnie Coro Radio amateur CO2KK Hi amigos radioaficionados, welcome to the weekend edition of Dxers Unlimited, which today will feature a re-run of an Antenna Topics section about the HENTENNA, as requested by a large number of listeners around the world that have written to me recently, as this Japanese antenna seems to be making headlines in radio publications around the world once again…
By the way, the original report here at Dxers Unlimited, dates back to 1999,more precisely, it went on the air the 12th of October of 1999, and according to my records, it generated a lot of interest from our listeners, who were at that time, 1999, getting ready to enjoy the peak years of solar cycle 23 !!! So here is once again at the request of Dxers Unlimited’s fans , the report on the HENTENNA, the Japanese elongated loop antenna with an easy match to coaxial cable feedlines of any impedance, be it 50, 60 ,75 or 93 ohms...or even 150 ohms !!! I recently built yet another HENTENNA for the FM broadcast band, and it is working nicely, having already pick up some Sporadic E skip DX stations from Mexico, the US and Puerto Rico during the just starting E skip season now in progress. Once again, remember that the HENTENNA produces or receives VERTICALLY polarized waves when the antenna is placed horizontally; that is, with the long sides of the loop pararell to the ground. AND, if you want horizontal polarization, just flip the HENTENNA so that the long sides of the loop are vertical, and the short sides are parallel to the ground, something that is puzzling, but that’s the way it is amigos… By the way, one of the world's foremost antenna experts, Dr. L. B. Cebik, amateur radio operator W4RNL, has done an extensive analysis of elongated loops, and his findings are really fascinating. Dr. Cebik specializes in computer modeling of complex antenna systems, and his work with the HENTENNA and other similar elongated loops shows that the HENTENNA is a very good performer indeed. For the benefit of those who could not pick up last weekend's Dxers Unlimited edition, I will repeat the formulas for calculating HENTENNAS in the frequency range from 14 megaHertz all the way up to the high TV band that here in the Americas ends at 216 megaHertz.. so amigos, stay tuned, I'll be back with more radio hobby related information in a few seconds... ………………. You are listening to Radio Havana Cuba, the name of the program is Dxers Unlimited… you can send your signal reports and comments via e-mail to [EMAIL PROTECTED] or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba… And now more about the HENTENNA. Dr. Cebik's computer modeling shows that the elongated loop HENTENNA has an edge over a regular square one wavelength loop and the regular elongated loop. HENTENNAS for receiving FM broadcast signals are very easy to build, using a wooden or PVC pipe frame and copper wire. I built the one just mentioned cut for 100 megaHertz, using PVC insulated no. 12 wire, the one that is typically used for home wiring. The loop was closed by soldering with a butane torch, and using regular solder with rosin core... The reason for using the butane torch is that no soldering iron at hand here could handle the heavy wire PLUS the high speed heat transfer of the copper wire. The loop for the 100 megaHertz antenna is 1.5 meters on the long sides of the rectangle and 50 centimeters on the short sides. The feed point for the 50 ohm cable is located about 55 centimeters from one of the short sides of the loop. The antenna is installed with the long sides in a vertical position; for receiving horizontally polarized FM broadcasts. I tried both 50 ohms and 75 ohms coaxial cables, and could not detect any difference on the weakest station that I am picking up here regularly with the FM band HENTENNA. Again, if you want to make of these elongated loops for receiving, here are the measurements to use: for the long sides of the rectangle 1/2 of a wavelength at the operating frequency, for the short side, the length is 1/6 of a wavelength... and the connection point for the coaxial cable of 50 ohms impedance is a little more than 1/6 of wavelength from one of the short sides of the rectangle. I have tried two different techniques for feeding the antenna, one using two wires connected to the long sides and going to an insulator to which the coaxial cable is attached... this is what I do with antennas for the lower frequencies. For the higher frequency antennas, like for example the TV HI VHF band, or the amateur two meter band, I use the coaxial cable itself, by carefully splitting the center conductor and the shield in two... it takes a little practice to do, but you will be able to do it, and it saves time and avoids one extra soldered connection. Do remember to fully protect the coaxial cable from the weather, by sealing it properly with PVC tape and silicone sealing compound... HENTENNAS can be built for any frequency between 10 megaHertz and 300 megaHertz by using heavy WIRE, and for the frequency range from about 50 megaHertz to 500 megaHertz you may try building HENTENNAS with copper or aluminum tubing. YES amigos, this is yet another easy weekend project... collect all the needed materials and have them ready at your workshop, the garage or near the kitchen table, so that this coming weekend you can build your own low cost elongated loop HENTENNA. Remember, if you are a radio amateur, that a HENTENNA is a very effective antenna to take along with your HANDIE TALKIE, as it will extend the range of the HT many times. I now have my portable HENTENNA for 2 meters that has shown a gain of more than 6 to 10 decibels above the handie talkie's rubber duck antenna. In other words, the HENTENNA is behaving as if you add a linear amplifier to the HT with the additional benefit that if DOES NOT USE UP EXTRA battery power. And one final comment, do remember that the HENTENNA is DIRECTIONAL, so you can turn it around for best possible signals... A HENTENNA for two meter band FM must be installed with the long sides HORIZONTAL... in order to receive and transmit the vertically polarized waves used for amateur 2 meter FM communications! Now our next item, here at the weekend edition of Dxers Unlimited: Radio amateurs running extremely low power transmitters are demonstrating that the ability of the ionosphere to send back to Earth radio signals is much better than what was previously thought. Running powers as low as 10 milliwatts, that is 20 db down from a 1 watt transmitter; two way contacts on the 20, 17,15 ,12 and 10 meter bands are nowadays quite regular... According to the experimenters involved in this fascinating milliwatting tests, when power goes down below about 100 milliwatts, QSB or fading is very severe, indicating that this may be very near the lowest possible limit for ionospheric propagation using standard CW Morse code. Using coherent CW or other computer-enhanced signal processing, it now seems like ultra-low power signals of 1 milliwatt or even less may be effectively used. Anyway, this is one more reason to join the ranks of those amateur radio operators who have decided to do their operating at low power or QRP levels... 5 watts on CW and 10 watts on SSB are nowadays more or less universally accepted as the maximum power for QRP stations. And one final comment about the ultra low power transmission experiments... 1 watt to 5 Watts power output transmitters can be built using very easy to obtain receiver type components, something that will allow many amateurs in less developed areas of the world to join us. One of the things that keep many potential radio amateurs from going on the air in less developed countries is the lack of appropriate transmission type radio components. With the QRP rigs, a defunct TV set, a dead boom box, or any other otherwise broken down or junk electronic gear may become the source of all the parts needed to make a homebrew radio station. ……….. Six meters opening up again via sporadic E, according to reports received from Europe, North America and the Caribbean, plus my own daily observations, the sporadic E clouds are once again providing that very interesting propagation mode for TV and FM band Dxers, and of course, to amateur radio operators too... The 30 meter amateur band operator is now becoming more and more popular during the low ebb of the solar cycle, because 20 meters is closing up much earlier due to the very low solar activity. Installing a 30 meter band elongated loop is easy , and offers excellent performance for DX work... The 30 meter band elongated loop antenna,is also simple to build, matches 50 ohm coaxial cable without any problems, or if you prefer it can be fed with open wire transmission line and then be useful on several bands for transmitting and short wave listening too. Do not forget that many amateur radio operators also enjoy listening to international short wave broadcast stations too, and that we use our amateur radio rigs to enjoy that aspect of the hobby too. Well, here is some information about this rather compact antenna, that radiates with a low departure angle, despite the fact that it does not need very high masts, as a matter of fact, you can use home brew masts made from bambusa-bambusa linnei, well bamboo, bambusa-bambusa linnei is the scientific name that botanic experts give to bamboo. Masts used by Cuban radio amateurs for this antenna are made of several sections of heavy cuban bamboo or cana brava, reinforced between sections by short lengths of aluminium tubing of appropiate diameter. The masts are some 9 meters high, or for those of you that still think in English measuring units almost 30 feet high. . The rectangular loop's vertical sections are 5 meter high, and the horizontal sections are 10 meter long. So, the loop is shaped like a rectangle that has its short sides of 5 meters length, and the long sides of 10 meters length. The short sides are the vertical ones, so that allows the lower horizontal section to be placed at 4 meters above ground, which is certainly not ideal,but is nevertheless good enough to make the loop generate an adequate vertical take off angle for DX work. Now, listen how the antenna is fed... The 30 meter band loop is fed using 50ohm coaxial cable, but you can use low cost TV type 75 ohm coax if you wish too. The feedpoint is at one of the upper corners of the antenna, as we want to take advantage of the elevated feedpoint placing the high current as high as possible!!! As I said a while ago, the 5 meter high and 10 meter long rectangular loop can be also fed with open wire line, something that will allow its use on other frequencies too. Using the coaxial cable feedline, the antenna is a single band antenna, capable of low SWR or standing wave ratio operation only on the 30 meter ham band that spans from 10.1 to 10.150 megaHertz. Similar aspect ratio loops can be designed and built for other amateur bands, and they offer to their users several important advantages over the classical single band half wave dipole. The first and most important one is that the rectangular loop is a very quiet antenna for receiving purposes, due to the fact that it is a closed element, then add to this that it does not need very high masts, plus that even when placed at a relatively close distance from ground, it does generate a nice and clean, low take off angle vertical pattern which is much better for DX work than the vertical pattern of a half wave dipole at the same height. Now, add to all this advantages its low cost and very easy installation, direct coaxial cable feed using either 50 or 75 ohm cable, and you will realize that the rectangular one wavelength loop is a very nice all around antenna. ---[Start Commercial]--------------------- Preorder your WRTH 2007: http://www.hard-core-dx.com/redirect2.php?id=wrth2007 ---[End Commercial]----------------------- ________________________________________ Hard-Core-DX mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/hard-core-dx http://www.hard-core-dx.com/ _______________________________________________ THE INFORMATION IN THIS ARTICLE IS FREE. It may be copied, distributed and/or modified under the conditions set down in the Design Science License published by Michael Stutz at http://www.gnu.org/licenses/dsl.html
