Radio Habana Cuba Dxers Unlimited Dxers Unlimited's mid week for 17 - 18 July 2007 By Arnie Coro radio amateur CO2KK
Hi amigos radioaficionados worldwide..., and those of you in space orbit too... with our now traditional salute, a special short form edition Dxers Unlimited's mid week edition begins , the reason for today's shorter program is that ready to bring you lots of practical radio hobby information... I am Arnie Coro, radio amateur CO2KK, your host here in Havana and here is item one: Many listeners have written asking about the possibility of using a single antenna for covering a wide range of VHF frequencies, so today in our ASK ARNIE section of the show, I will be telling you about two popular antennas that offer broadband coverage ... one is omnidirectional and the other has a directional pattern. Item two: Another antenna related topic...by using a pararell open wire feedline connected to a dipole, you can actually operate the system as three antennas with very different characteristics... Mode ONE: as a standard dipole, MODE 2: as a T antenna working against a good ground system and MODE 3: As an inverted L by using one leg of the open wire feeder against ground... By arranging for the proper switching, the THREE IN ONE antenna system provides you with a lot of possibilities. At CO2KK, my ham radio station, I have a three wire on each leg fan dipole fed with 400 ohm open wire line... The fan dipole by itself is an excellent antenna for the frequency range between 7 and 21 megaHertz, using a wide range PI network antenna tuner... By connecting together the two wires of the transmission line, the antenna works very nicely on the 80 meters amateur band in what is known as a T antenna configuration, but it does need a counterpoise, or ground system in order to work properly as a T antenna. I also use it with just one of the wires of the open line , so that the antenna works as an inverted L..., again working with a ground system. So, now you know why I have named this system the THREE IN ONE ANTENNA... By making the legs of the dipole at least 10 meters long , an excellent frequency coverage is achieved...For the lower frequencies, longer legs improve the performance of this antenna a lot. More radio hobby related information coming up as Dxers Unlimited's mid week edition continues in a few seconds ...... Si amigos, you are listening to the mid week edition of Dxers Unlimited, and as announced at the start of the program , here is LA NUMERO UNO, the most popular section of the show, ASK ARNIE. answering a request about broadband antennas for VHF monitoring... By the way,monitoring VHF communications as well as the VHF amateur bands is one of the more than 81 ways of enjoying the radio hobby... But , monitoring the VHF range from about 40 megaHertz all the way up to about 170 megaHertz requires using a broadband antenna... For general purpose monitoring 360 degrees around the compass, there is one antenna design that works very well, and is not too difficult to homebrew... it is known as the DISCONNE ANTENNA, and I happen to have at hand here, ready to be sent to any Dxers Unlimited listener wanting to build a DISCONNE, an excellent design program... The freeware program lets you calculate a DISCONNE is less than two minutes... And I can assure you that antennas built following the dimensions obtained from the disconne design software work very well indeed... My two favorite designs for discones are one that has a low frequency cuttoff of around 40 megaHertz , with theoretical, but not in actual practice high frequency limit of 400 megaHertz, and another design that starts operating around 100 megaHertz and that will again, in theory will reach as high as 900 megaHertz or even higher... From the above information you can see that the frequency range of a typical disconne is almost a ten to one frequency ratio...but there is a problem with these antennas as the frequency goes up.You will still have a nice match, typically less than 2 to 1 standing wave ratio, but the take off angle will move upward as the frequency changes to a higher value, this shift in the vertical take-off angle of the discone is an outstanding characteristic of this unique antenna system, that is fed directly using 50 ohms coaxial cable, and requires absolutely no matching system... QSL , yes QSL on the air amigos... QSL on the air to the many Dxers Unlimited's listeners that have sent e-mail messages to [EMAIL PROTECTED], requesting a QSL card from Radio Havana Cuba, sending very accurate reception reports and providing me with many good ideas on how to improve the program...now , here is our next item of today's show... This is the technical tips section of Dxers Unlimited... today I will tell you about how to reduce power line interference by installing a power line filter between the wallplug where you connect your radio equipment and the radios... A three section homebrew filter, with a proper ground connection prevents power line noise from entering your radios and causing harmful interference... There are several well built, but expensive , power line filters, so your best option is to homebrew one, just as I have done here at my listening post and ham radio station. The filter is capable of passing an AC power line current of 6 amperes, more than enough to power up all my equipment, except the high power linear amplifier...The power line filter is very effective in removing noise coming from nearby switched mode power supplies , like the ones used by computers. I am now working on a step by step instruction manual with full graphics, so that you can homebrew this type of filter, that does require a lot of metal work, as it most be totally shielded in order to be really effective. As soon as the manual is completed, I will be announcing it here at Dxers Unlimited... ...... [EMAIL PROTECTED], that's my direct e-mail address, [EMAIL PROTECTED], always ready to receive your comments about the program, signal reports, QSL requests , and any radio hobby related questions that you may want to send to our popular ASK ARNIE section of Dxers Unlimited... And now amigos, as always at the end of the show, our exclusive and not copyrighted HF plus low band VHF propagation update and forecast...Solar flux is hovering now very near the baseline activity... latest reports show that the flux was around 72 units, just five units above the 70 figure that scientists consider to be the minimum baseline activity ... The effective sunspot number was at ___30____ at around noon local time here in Havana, and the A index was a nice and low 02... Expect propagation to improve somewhat by Thursday, when the effects of the solar wind will vannish... Hope to have you listening to my show's weekend edition next Saturday and Sunday UTC days... and don't forget to send me your signal reports and comments to [EMAIL PROTECTED], or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba. ---[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
