Radio Habana Cuba Dxers Unlimited Dxers Unlimited's weekend edition for 3-4 November 2007 By Arnie Coro Radio amateur CO2KK
Hi amigos radioaficionados worldwide... with our traditional salute, Dxers Unlimited’s weekend edition begins, 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 a popular antenna that offers broadband coverage. It is omni directional, that meaning it receives signals from all around the compass and also it is not too difficult to homebrew. Item two: Another antenna related topic...by using a parallel open wire feed line connected to a dipole or how it is known among experts a FAN DIPOLE,, you can actually operate the system as three antennas with very different characteristics... Mode ONE: as a standard half wave 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 of course that it does need a ground return made, at my location by several ground radials or what was known in the early days of radio as a “counterpoise”. I use one of the wires of the open line, in another configuration, so that the antenna works as an inverted L... 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, excellent frequency coverage is achieved... More radio hobby related information coming up as Dxers Unlimited's weekend edition continues in a few seconds ..... Si amigos, you are listening to the weekend 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 DISCONE 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 DISCONE is less than two minutes... And I can assure you that antennas built following the dimensions obtained from the discone design software work very well indeed... My two favorite designs for disconnes are one that has a low frequency cutoff of around 40 megaHertz , with a high frequency limit of 400 megaHertz, and another design that starts operating around 100 megaHertz and that will reach as high as 900 megaHertz or even higher... From the above information you can see that the frequency range of a typical discone is almost a ten to one frequency ratio... an outstanding characteristic of this unique antenna system, which is fed directly using 50 ohms coaxial cable, and requires absolutely no matching system... Again, you can homebrew disconnes for any frequency range, with the design parameters that you feed to the computer software program... A friend of mine , who spends most of his spare time monitoring the aviation band in the range from 118 to 136 megaHertz , has built a discone with a low frequency cutoff of 110 megaHertz, that he has tested all the way up to the 800 megaHertz frequency range very successfully. His antenna was built during a weekend, using copper wire and a small piece of Plexiglas insulation to separate the cone from the disk... He used an aluminum disk for the top of the antenna, and copper wire spokes to form the cone... More about broadband antennas for VHF monitoring after a short break... ..... You are listening to the weekend edition of Dxers Unlimited, coming to you from Radio Havana Cuba, and for those listeners that have requested the data file about the QUATRRO CRYSTAL RADIO RECEIVER, let me tell you I made a new drawing of the schematic diagram, as the original file was yet another computer crash casualty... So, be patient amigos, I will e-mail the four diode crystal radio diagram by the end of the week... Now, the program continues with information about the second type of broadband antenna for VHF monitoring. In this case, it is a directional system, known among experts as a log periodic array of dipoles...This antenna is rather complex from a mechanical point of view, but it can be built using the proper tools and following a good design. My favorite log periodic for VHF monitoring covers from 45 megaHertz to 150 megaHertz, and it does require the use of an antenna rotor. A second smaller log periodic for the frequency range 100 to 500 megaHertz has provided excellent service for monitoring, as well as for operating the two meters, one and quarter meters and 70 centimeters amateur bands... Again, home brewing a log periodic antenna is not a very easy job, but believe me amigos, that time spent building your own log periodic for VHF-UHF monitoring is well worth every single minute you devote to its construction...and you will certainly save a lot of money, as commercially built log periodic antennas are very expensive. The typical log periodic antenna is also designed for 50 ohms coaxial cable feed, and again, it is a highly directional system that requires the use of a rotor to pinpoint the antenna in the direction you want to pick up signals or to transmit. There are several very well written software programs for designing VHF and UHF log periodic antennas, and I have here two of them, ready to be e-mailed to any of you Dxers Unlimited's listeners around the world that may want to explore the possibilities of home brewing your own broadband log periodic antenna... ....... 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 wall plug 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 TV sets VCR and DVD machines. 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... You are listening to the weekend edition of Dxers Unlimited, that goes on the air Tuesdays and Wednesdays UTC days.... and here is our next item of today's program... Satellite direct broadcast radio is very slowly growing in listenership, but this is happening only in developed countries... the number of satellite radio receivers capable of picking up direct broadcasts from Earth orbit in third world nations is extremely small, something that can be easily explained for two obvious reasons... one, the receivers are much more expensive than common radios AM broadcast band short wave and FM radios... and two, most of satellite radio services require paying for a monthly fee that in many cases may be easily the equivalent of what a person in some places of Africa , Latin America or Asia, receives as income for many months of hard work... So, short wave radio is here to stay amigos ... and yes, we may see more satellite radio receivers sold in Third World nations, but only to people of above average income...who can pay for the radios, and also for the monthly fees asked by the operators of the existing satellite radio systems... ... 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 continues in its now almost endless hovering very near the baseline activity... latest reports show that the flux was around 67 units, just three units above the 64 figure that scientists consider to be the minimum baseline activity ever registered ... The effective sunspot number was very low at around noon local time here in Havana, an SSN of 6 . Expect HFpropagation to continue to be very poor .The optical sunspot count was ZERO, again ZERO, and expected stay at zero or very slightly above for the rest of the week. Hope to have you listening to my show's midweek edition next Tuesday and Wednesday 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
