Radio Havana Cuba Dxers Unlimited Dxers Unlimited weekend edition for 22-23 December 2007 By Arnie Coro Radio amateur CO2KK
Hi amigos radioaficionados ! Seasons greetings and a Happy New Year 2008 from Havana… Welcome to the weekend edition of your favorite radio hobby program, coming to you from sunny Havana, where our mild winter weather, as usual is providing us with beautiful days for going to the beach !!! I am Arnie Coro, radio amateur CO2KK, your friend here in Cuba, now ready to read today’s menu: ITEM ONE The expected TV DX winter season openings have happened, recently, with sporadic E skip events around the Caribbean becoming more and more frequent. At least two of the most recent sporadic E opening sent the maximum useable frequency up to the FM band, making reception of FM stations from more than one thousand miles away possible even with handheld radios and their telescopic whip antennas… More about the sporadic E season later. This is the winter sporadic E season that is much shorter and with less number of openings than the spring summer season,that is still several months away, due to start at the end of April as usual .. ITEM TWO: An amateur radio satellite designed to orbit the Earth using a very special elliptical orbit that would make it available for many hours at a time, just short of a geosynchronous orbit, the so called MOLNYA orbit, is an excellent choice for any upcoming new ham radio satellite. But it will cost a lot of money to build it. Such a MOLNYA orbit type of satelllite will hopefully sometime in the distant future replace the doomed OSCAR 40, that had big problems from its very few hours in Earth Orbit. ITEM THREE: Listeners questions continue to come in via e-mail, postcards, letters and fax messages, and I have quite a backlog of them here waiting to be answered… a recent one from Brazil, really surprised me, as normally the show is not heard so far South of Havana… But the use of 11760 kiloHertz with our high gain omnidirectional antenna explains why English speaking listeners from Brazil, Argentina, Chile, Uruguay and Paraguay and also Bolivia, among others, are picking up Dxers Unlimited.. ITEM FIVE: More about low cost , easy to build ham radio equipment, and at the end of the show, our exclusive and not copyrighted HF plus low band VHF from 30 to 120 megaHertz propagation update and forecast.Stay tuned for more radio hobby related information, coming to you from Havana. I am Arnie Coro ready to be back with you in just a few seconds after a short musical interval… …. Si amigos, yes my friends, you are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and YES, we do QSL here one hundred percent, we do verify reception reports and we do it absolutely free of charge, as all short wave radio stations should do… Send your signal reports and comments about the program to [EMAIL PROTECTED], or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba, And NOW , here is ASK ARNIE, THE most popular section of Dxers Unlimited, according to your e-mails, postcards and letters amigos … QUESTION number one for today: From listener Desmond QTH Glasgow, Scotland, the UK…, Des wants to know why old radio magazines often mentioned the use of so called converters ahead of short wave receivers to pick up the higher frequency bands. Well amigo Des,as I explained recently here to a listener in Maryland , USA, a converter is nothing else but a complete front end of a radio receiver,that is built as a separate unit, in a separate box ,so that it can be connected between the antenna and the receiver and it usually includes a radio frequency amplifier stage, a mixer and a local oscillator. The RF stage in the case of converters designed to be used for the VHF bands used at that time,the best available low noise vacuum tubes that provided good gain and low noise, and the really good converters used a crystal controlled local injection oscillator. Even today, adding a homebrew converter ahead of a low cost receiver can provide outstanding results,it can prove to be a quite succesful effort especially with radios that lack front end selectivity or use a single intermediate frequency, the so called single conversion receivers. Not too long amigo Desmond, I removed a lot of dust from a three transistors 10 meters band converter that was in storage for many years… it required just 12 volts DC to operate. Powering it up from one of my workbench power supplies , I connected the more than 30 years old germanium transistors converter to a modern digital portable receiver,the SONY ICF7600 and was pleasently surprised when I could pick up several 27 megaHertz 11 meters band Citizens radio stations as the band was open at the time of the test. Modern HF receivers are including extended tuning range even up to the two meters amateur band, so these converters are not required with new receivers, but older radios that had a limited coverage to around 30 megaHertz would certainly benefit with the use of a well designed converter. Anyway, for those of you like amigo Desmond that are interested in VHF converters, I may add that they are not too difficult to homebrew, especially if you use solid state devices . A typical more modern converter will use a high gain low noise MOSFET RF amplifier stage, a double balanced passive mixer and a bipolar transistor oscillator. It will be powered from 12 volts DC and when connected to even a low cost modern digital receiver, will turn the resultant combination into a rather nice VHF receiver , useful for monitoring 6 meters during the summer sporadic E season. Remember to tune set the receiver to scan from 50.0 to 50.3 megaHertz where most of the activity on 6 meters is concentrated around the world. QUESTION TWO, Came from the beautiful city of Bahia in Brazil, listener Marco Aurelio , who listens to our 9550 kiloHertz Caribbean edition, tells me in his e-mail that he wants to know more about the fan dipole antennas and why are they so useful when you can only install a single outdoor antenna at your location.. Well amigo Marco Aurelio, broadband fan dipoles are easy to build, they are easy feed with open wire line, and above all, receive only fan dipoles can be built very easily and at low cost by anyone . Amigo Marco Aurelio, I am sending direct to you via e-mail the complete , step by step building instructions for my WIDE BAND FAN DIPOLE HF ANTENNA SYSTEM, so that you can start building yours and then tell me also via e-mail how it performs at your location. The WIDE BAND FAN DIPOLE HF ANTENNA is possibly one of the lowest cost high performnce OUTDOOR antennas that exists, but it can also be used INDOORS too, in which case you will want to install a remote tuning ANTENNA TUNER system. Peaking the antenna tuner for maximum signal is quite easy to do, and at the same time it provides ultra-sharp selectivity right at the antenna, that helps a lot to reduce unwanted noise and cross modulation problems caused by high powered stations that affect low priced receivers so badly. As a matter of fact, using my WIDE BAND FAN DIPOLE ANTENNA with a low cost digital receiver proved to be a very interesting experience, as the radio’s performance was enhanced signficantly due to the extra selectivity at the front end provided by the antenna tuner system very sharp tuning. QUESTION THREE, yes, sent by listener Adalberto in Mexico |City, Mexico, he wants me to describe the design parameters for the low cost two element cubical quad antenna for the 2 meters amateur band. Well amigo Adalberto, using standard wire quad antenna elements , the small CUBICAL QUAD is fed with 50 ohm coaxial cable. The boom is made from PVC pipe of the type used for water distribution .The two elements are close spaced at only 25 centimeters separation from each other. This version of the CUBICAL QUAD antenna has around 5 dB gain, a broad radiation horizontal pattern, is rugged and easy to build and will help you to access distant repeaters that can’t be reached using the typical handie-talkie helically loaded antenna, popularly known as rubber ducky because they look like the tail of a duck wagging !!! The boom of the antenna is made from PVC pipe of the type used for high pressure water distribution, and is one meter long, so that you can hold the antenna to any support from the rear of the reflector element and keep it well separated from the supporting mast or tower. Again the separation between the driven and the reflector loops is 25 centimeters. And the wire loops are made using number 12 bare copper wire.. I feed this antenna with 50 ohm coaxial cable, and right after the feedpoint, I wind 8 turns of the coaxial cable to the boom of the antenna to make an RF choke.. the cable is then fed trough a hole in the boom to the rear of the antenna where it exits . I have made many of these antennas, and found out that they provide excellent performance, and when built using the above mentioned dimensions they are usually below 1.5 to 1 standing wave ratio even before any adjustments are made. They can be adjusted for almost perfect standing wave ratio by just sliding the reflector element back and forth across the boom, and then leaving it permanently fixed at the spot that provides the lowest SWR. Try to tune the antenna for minimum SWR using a VHF standing wave ratio meter, but again, you can use the antenna directly without any adjustments without fear of high SWR, by just carefully measuring the elements . And now amigos, as always, at the end of the program, here is Arnie Coro’s Dxers Unlimited’s HF propagation update and forecast… Solar flux is hovering around 70 units and the A index was still a around 8 units, and it may even go down later in the week.Solar flares are not expected during the rest of the week .But propagation conditions will take a turn for the worst because of what scientists are forecasting as yet another long period of a blank Sun,. Sporadic E openings are going to be more frequent as we approach the peak of the winter E skip season, so do monitor the low band TV channels for them. See you all at the mid week edition of the program and don’t forget to send me your radio hobby related questions, signal reports and comments .. send mail to : [EMAIL PROTECTED], or via air mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba ---[Start Commercial]--------------------- Order your WRTH 2008: http://www.hard-core-dx.com/redirect2.php?id=wrth2008 ---[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
