Dxers.. Unlimited Dxers Unlimited’s weekend edition for Sept 8 -9 2007 By Arnie Coro Radio amateur CO2KK
Hi amigos radioaficionados ! Equinoctial propagation just about to be in full swing all around the world , and lots of Dxers Unlimited’s listeners are already enjoying it according to the reports that I am receiving at my e-mail address, [EMAIL PROTECTED] Several experienced amateur radio operators say that even the slight propagation disturbances of the past several days have helped in a way, by providing some unique contacts from stations not normally heard on some bands. Ionospheric absorption is also rather low, precisely due to the rock bottom low solar activity prevailing during the past several days and that helps too… Item two: QSL on the air to the many Dxers Unlimited’s listeners that send questions to my program. YES, there is a cue or waiting line of sorts, but I have found out that many questions are quite similar and that helps to answer them on the air to many listeners at the same time.. Perhaps the wording was a little different but the essence of the question is the same… That explains why in some programs I make reference to questions sent in by listeners in several countries… Item three: Talking about questions, a ham radio operator asked recently while we were in a two way SSB contact on the 20 meters band what he could gain by changing his three element monobander , replacing it by a 13 element log periodic array. He was quite shocked when I said that on the 20 meters band he would gain absolutely nothing !!! Then , the lengthy explanation about how the log periodic arrays really work followed, and my Canadian friend found out that a typical log periodic Yagi array for the HF bands provides the operator with what could best be described as an almost infinite number of three element Yagis from the lower cutoff frequency to the antenna’s highest possible operating frequency… More about the very interesting wide band log periodics in today’s Dxers Unlimited’s antenna topics section. Item four: My CW key here is a retired computer mouse… yes, I heard that on the popular 30 meters CW amateur band the other day… and I was really happy when the operator sending that explanation about his CW key added that he got the idea by listening a few years ago to Radio Havana Cuba’s Dxers Unlimited’s program… As you can guess amigos, that literally “” made my day “”… Today we will also feature our most popular section of the show, YOU HAVE QUESTIONS, and Arnie tries to answer them, and as always at the end of the program, our exclusive and not copyrighted HF plus low band VHF propagation update and forecast. Stay tuned for more radio hobby related information, right on this same frequency or web connection. I am Arnie Coro in Havana, back with you in a few seconds. ….. Si amigos, sure, playing with antennas is one of the 81 ways you and I enjoy playing with our radios… and here is our ANTENNA TOPICS section, today devoted to a particular antenna, a very special one indeed that has become the mainstay of many HF communications systems and that is also finding use among the world’s international short wave broadcasters… I am talking about the LOG PERIODIC YAGI antenna array… The LOG PERIODIC YAGI is certainly a beautiful looking antenna, and for those needing instant frequency changes trough a given range , the LOG PERIODIC is an ideal antenna indeed. LOG PERIODIC antennas for the range between 10 and 30 megaHertz are now quite popular, but you will also find much larger versions designed to operate from 6 to 22 megaHertz, especifically targeted for international broadcast stations use. Amateur radio operators with a very affluent budget have also benefitted from the log periodics, but in my opinion, they are not really worth the investment for ham radio use. A 10 to 30 megaHertz LOG PERIODIC is a really large antenna by all standards, and that’s why some antenna manufacturers are offering a somewhat smaller version for operating above 20 meters, that is , an antenna with its lower frequency limit set at 13 megahertz and its upper frequency limit at 30 megaHertz.The size of such 13 to 30 megaHertz LOG PERIODICS is much more manageable for a typical amateur radio installation, and such antennas may have from 7 to 15 elements, with the ones with more elements offering better performance. A 13 to 30 megaHertz log periodic YAGI will provide the operator with the possibility of operating on the 20, 17, 15, 12 and 10 meter bands, so it is a 5 band antenna for ham radio, plus an excellent receiving antenna for short wave listening on the 22, 19, 16, 13 and 11 meters international short wave broadcast bands. And of course that the user can also pick up many communications services, the so called utilities that operate using that range of frequencies. A 13 to 30 megaHertz LOG PERIODIC antenna for your amateur radio station is certainly an expensive antenna if you build it properly, and it does require a heavy tower and a heavy duty antenna rotor to handle it. Now, for the real world gain figures… the typical LOG PERIODIC is more or less the equivalent of a three element YAGI array on any frequency all along its operating range…You may read some absurd claims from antenna manufacturers, but all tests and computer modelling will take you to the same ballpark figures, about 6 to 7 dB gain over a half wave dipole… Log periodic antennas for VHF and UHF frequencies are another different story, as size is not then a limitation, and the designer can look for more gain without having to worry about mechanical considerations. One of my favorite TV and FM band Dxing antennas is a 13 element wire LOG PERIODIC designed to operate from 50 to 200 megaHertz, a four to one frequency ratio. It’s a nice looking antenna, it’s lightweight so I have also used to operate a portable station on the 6 and 2 meters amateur bands. You can learn a lot about LOG PERIODIC ANTENNAS by running a search on one of the popular Internet search engines and downloading some of the very interesting scientific and technical papers available on the web about these antennas, or you can also go directly to my good friend’s Dr. L.B. Cebik website and look for his authorized opinions about the log periodics… the URL is www.cebik.com, again, www.cebik.com, and I am sure that you will really enjoy visiting that unique site amigos ! …… This is Radio Havana Cuba, the name of the show is Dxers Unlimited, and here is now our popular, la numero uno !!! You have questions and you make me work hard to answer them amigos !!! Today’s question was sent by several listeners in the USA, Mexico, Jamaica and Canada. They all want to know what is the lower power of radio frequency energy that will make possible a two way radio contact via the ionosphere… In other words, what’s the known minimum power that will bounce back to Earth from the ionosphere. ANSWER: According to accounts by well known QRP or low power amateur radio operators, powers as low as microWatts or millionths of a Watt of power. When HF propagation conditions are at their best, with minimum ionospheric absorption and low noise levels, radio amateur QRP or very low power rigs running 5 Watts or less are able to sustain excellent two way contacts. Reducing power to the 1 Watt level increases the challenge, and that’s exactly what many of us, QRP operators do, in order to really test our antennas and receivers , and of course our operating skills… Going down the MILLIWATT or thousands of a Watt level is a greater challenge… but let me say that there are now several radio amateurs that have worked more than 100 Dx entitities using powers in the 100 milliWatt range. With such low power levels, you do need very good antennas, an excellent receiver and last but not least, good propagation conditions. My 2 Watt power output 40 meter band CW rig is a good example of what I am talking about… running that rig on the 7 megaHertz or 40 meters amateur band is very enjoyable, as that part of the short wave spectrum provides unique propagation conditions at certain times of the day that make possible excellent two way contacts while running low power. So amigos who asked, there you are, powers as low as millionths of a Watt do propagate using the ionosphere as a turn around point, but more typically powers around 1 Watt or so are considered the lower practical limit for HF ionospheric communications . ….. You are listening to the weekend edition of Dxers Unlimited coming to you from Havana amigos… you can get in touch with us by sending an e-mail signal report and comments about the program directly to [EMAIL PROTECTED], or VIA AIR MAIL, a postcard will be OK and cheaper too, just send me your postcard report to Arnie Coro, Radio Havana Cuba, Havana, Cuba, and I’ll be very happy to QSL back to you , so please don’t forget to send your postal mailing address with your e-mail messages… Now Dxers Unlimited continues with TIPS and TECHNNIQUES a new section of the program that is on the air today for the first time: Todays’ TIP… how to select the best possible headphones for your short wave radio… By all means avoid the HI FI headphones, you don’t really need and don’t want wide band audio reproduction when listening to short wave signals… The best headphones for listening to HF radio are the ones used by aircraft pilots that are specifically designed to optimize voice communications.. Sure, I agree, they are quite expensive, but they do last a very loooong life. You can find information about aircraft type communications headsets at any aviation supply dealer…again, they will be expensive, but you will also get a nice high quality noise cancelling microphone that forms part of the headset, so that you will be able to use it with your amateur radio station too… and this was our TIPS and TECHNNIQUES section of Dxers Unlimited today amigos.. And now , just before going QRT, here is our exclusive and not copyrighted HF propagation update and forecast… Sunspot number standing now ZERO, yes you heard it right, it can’t go lower, its ZERO sunspot count and the solar flux is also at rock bottom level of 67 units, and for your information scientists consider a totally quiet Sun radiating 65 flux units … No data from the farside of the Sun available so it is difficult to know what is going to happen in the next few days but despite those ugly numbers during the rest of the week I see rather good propagation conditions on the HF bands, something you can find out by monitoring the bands , especially during the sunrise and sunset periods, local time. Be on the lookout for some nice DX on the 60 meters Tropical Band, where you can now find Radio Rebelde’s 5025 kiloHertz transmitter that is on the air 24 hours a day. See you all at the weekend edition of Dxers Unlimited amigos, and don’t forget that your e-mail messages , postcards and letters are really important to keep the show as useful to radio hobbysts as possible… send mail 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
