Radio Habana Cuba: Dxers Unlimited mid-week edition for 03 October, 2000
By Arnie Coro, radio amateur CO2KK
Hi amigos! Welcome to the mid-week edition of your favorite radio hobby program. I am Arnie Coro here in Havana; join me for some sixteen minutes of all radio hobby-related information.
Here is item one: While hurricane Keith was battering Belize and the southern portion of the Yucatan peninsula of Mexico, amateur radio operators in the affected area managed not only to keep their stations on the air, but also to provide extremely valuable weather data, including rainfall...
Item two: 5 active solar regions now visible, but they are all rather small, nothing like the huge region 9169 that disappeared from sight Saturday, but not before producing the long-awaited class X flare. Due to its position relative to Earth the big flare will not affect our planet's magnetic field at all.
Item three: Want a really portable antenna for HF, one that can be made in a couple of hours with hardware store readily available supplies? Then stay tuned for a detailed explanation on how to build Arnie's MAGIC TAPE ANTENNA... which will follow in a few seconds.
The sound engineer is Margarita Delgado; she is also my producer, and we both enjoy very much receiving your e-mail and Air Mail comments about the show... send them to arnie@radiohc.org, and VIA Air Mail to Arnie Coro, Radio Havana, Cuba, Havana, Cuba.
You are listening to the mid-week edition of Dxers Unlimited coming to you from Radio Havana Cuba... and now here is item three in detail, Arnie's MAGIC TAPE ANTENNA... an ultra-portable low-cost easy-to-tune-up short wave antenna system which is built using two steel measuring tapes. Try to obtain the highest possible quality measuring tapes, and be sure that they are at least 25 meters long if you want to build an antenna that will tune down to the 6 megaHertz band. For a more compact version, a measuring tape about 15 meters or maybe a little longer, let's say 50 feet, will be ideal. I have even made a portable measuring tape dipole antenna for the 20 meter to 6 meter band range with an even shorter length tape; in this case, I used two nice steel very flexible measuring tapes which are about 6 meters or almost 20 feet long.. Remember when you go out shopping for the measuring tape, try to obtain the highest quality ones, and you may even want to buy a spare one just in case there is a failure of the retracting mechanism. The half-wave dipole antenna made from the measuring tapes is simplicity itself. I made a center insulator block from hard polyethylene, fixed the two tapes to it, and connected a one-to-one ferrite balun to the feedpoint. The antenna can be extended to whatever length is needed to make it resonate ... and in order to assure a positive connection, a good contact with the tape, I carefully sanded away with emery cloth small lengths of the measuring tape at the start, so that two lengths of flexible braid from a coaxial cable could be soldered.
The rest I leave to you... This is a field antenna at its best: Just extend the measuring tapes to equal lengths, and your Arnie Coro's MAGIC TAPE ANTENNA will resonate to the desired frequency. I use dacron rope fixed to the measuring tapes, so that I can hang the antenna from any existing supports. The MAGIC TAPE ANTENNA can be used as an inverted V when only one central support structure is available; you can also install it as a sloping dipole, and if two supports are available, you can set it up as a regular half-wave dipole. NOW, this is a balanced antenna, properly fed via a balun, so you can use 50 ohm coaxial cable like RG58U, which is both lightweight and rugged enough to handle the typical amateur 100 watt transceiver... In order to obtain full benefits from the MAGIC TAPE ANTENNA, I carry a plasticized card with a table of antenna length versus frequency of operation. This is of course a start-up point, as I always trim the tape's length to minimum Standing Wave Ratio for the frequency I want to operate. If you are not going to transmit with the MAGIC TAPE ANTENNA, then just set up the length to the center of the band you want to listen to, for example, if you are out in the field and want to monitor the 19 meter international short wave broadcast band, set the length of each tape to a little less than 5 meters, and you will obtain excellent reception.
The great advantage of this field antenna is that you only need to carry a very compact and lightweight system to operate multi-band... AND for those of you who may be worried about the efficiency of the MAGIC TAPE ANTENNA due to the conductivity of the steel tape, let me say that the tests I ran when the first one was built here included installing a full-size wire dipole with its balun, and in the middle of a QSO, taking it down, and replacing it with the MAGIC TAPE ANTENNA. I did that several times and not one station that I was talking to noticed any difference! Theoretically there is, of course, a difference, but in actual practice, and that's what counts, it is so insignificant that you will never notice the difference between the copper wire dipole and the steel tape antenna. AS A MATTER OF FACT, there are several professional communications systems that include measuring tape antennas or a look-alike among the accessories of their emergency field stations!!!
This is Radio Havana Cuba, the name of the show is Dxers Unlimited, and YES, if you have any radio hobby related question, I'll be more than happy to try to answer it here at the YOU HAVE QUESTIONS and ARNIE HAS THE ANSWERS section of the show. Here is today's question: It came from a listener in Sweden and he wants to know what is the minimum power that can be used to communicate via short wave. Well amigo, that's a nice question, and let me tell you that amateur radio operators, using the 28 megaHertz or 10 meter band, where ionospheric absorption of radio waves is at a minimum, have made two way contacts using less than one milliwatt, or one-thousandth of a watt. And I am talking about long-range contacts using the F2 or the E layer of the ionosphere; these are not ground wave contacts, amigo.
So, amazing as it may seem, there is one sure thing about this; the Earth's ionosphere can support extremely low power communications when propagation conditions are really good. These contacts usually happen when the path is open for a frequency very near to the maximum useable frequency at that particular moment, and many radio amateur operators have run tests reducing power in 10 dB steps, only to be surprised to see that the QSO may continue even when they go from 1 kiloWatt to 1 watt, and that is a 30 dB difference!!!
Send your radio hobby related questions directly to me via e-mail, mail to: arnie@radiohc.org, or via Air Mail if you don't have access to INTERNET e-mail... send your postcard or letter with your radio hobby questions to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
And now amigos, as always at the end of the show, here is Arnie Coro's HF plus 6 meters propagation update and forecast. The actual number of sunspots Tuesday was very near 190, an indication that the background solar activity is still good enough for daytime maximum useable frequencies to soar even above 40 megaHertz on some paths. Ionospheric absorption at lower frequencies is, as expected, much higher now than when the number of sunspots was below 100, so don't expect to pick up much Dx in the range from 2 to 5 megaHertz.... Daytime reception on the 13 meter or 21 megaHertz international short wave broadcast band is expected to be excellent around the world, and around local sunset you may be able to enjoy a nice propagation enhancement in the range from 20 all the way up to 50 megaHertz, and that's good news for the 6 meter amateur band operators!
See you at the weekend edition of the show next Saturday and Sunday UTC days... AND don't forget that feedback from you the listener is essential to make this twice-weekly radio hobby show attractive to both beginners and experts, amigos!
Arnie Coro CO2KK
Havana, Cuba
03 October, 2000Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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