DXERS UNLIMITED'S WEEKEND EDITION FOR 13-14 JUNE 2009

CO2KK   Hi amigos radioaficionados around the world, and especially those of you that are now very near the summer solstice of the Northern Hemisphere, where most of Dxers Unlimited's listeners live... Those of you living below the Equator will soon be arriving at the winter solstice, that will provide much better propagation conditions than those existing for us living above the Equator. But in compensation for the poor and very poor DX conditions during the peak of the summer season , we will be enjoying a lot of Sporadic E skip events, that at time may send the maximum useable frequency curve well past the one hundred megaHertz mark. I am Arnaldo, Arnie, Coro, your host here at Radio Havana Cuba's Dxers Unlimited, our twice weekly radio hobby show that among other things provides an exclusive section devoted to answering your radio hobby questions, those questions that when answered properly will help you to enjoy more every minute dedicated to playing with your radios , antennas and accessories . Item two: Sporadic E events if and when they happen in coincidence can produce amazing DX contacts... well documented observations have demonstrated that the so called double hop skip is much more frequent than what many radio enthusiasts think, and that triple hop and even quadruple hop DX via sporadicE are perfectly possible. As a matter of fact, every summer season from around 1998 , we are seeing many instances of Transatlantic DX on the 6 meters amateur band. The European amateurs started to be allowed to operate on 6 meters when the so called Band One Television stations began to be phased out. Six meters is becoming very popular among amateurs in Europe, and they are using now high gain antennas and sophisticated digital signal processing receivers that make possible picking up very weak stations... Si amigos , yes my friends, oui mes amis , even with so very low solar activity still present,Sporadic E is filling the gap quite well, and those E skip openings will continue to happen until the end of July and perhaps Early August. Stay right on this frequency or connected to our streaming audio , in a few seconds after a short break for station ID , Dxers Unlimited's weekend edition will continue. I am Arnaldo, Arnie Coro radio amateur CO2KK your host here in Havana.... .................... You receiver is tuned to Radio Havana Cuba, or is it maybe that your computer is connected to www.rhc.cu... anyway, this is Dxers Unlimited reaching you when the Sun is once again showing very low activity, with the sunspot count down to zero for several days. At the end of the program I will provide you with a complete propagation update and forecast. Now here is item three of today's program... The Technical Topics section , that today will be devoted to part two of our minimum parts count , no rare or hard to find parts, single band amateur transceiver. This is now the description of the transmitter module,that was designed also for both easy assembling and so that repairs could be made without requiring the use of a magnifying glass and ultra miniature soldering iron. Amigos, this is a follow up of the Hurricane Two transceiver that provides about 10 Watts of output power on the 160, 80 or 40 meter bands , although our main purpose with the rig was to optimize it for 40 meters operation. 40 meters is the most popular amateur band here in Cuba, and it is able to provide excellent links by means of the Near Vertical Incidence Skywave propagation mode , also known by hams as the "cloud warmer mode" because signals are sent straight up into the ionosphere using antennas placed very close to the ground. Well, the fact is that with power outputs from 10 to 25 Watts it is possible to keep a very good quality link on 40 meters during local daytime hours between two nearby locations without having to use any type of repeaters. Our new transceiver design uses silicon output transistors originally intended for Citizens Bands radios working on the 27 megahertz or 11 meters band, so they are still easily available and don't cost a lot of money. The transmitter module begins with a computer aided designed audio pre-amplifier that has the frequency response curve especially optimized for voice frequencies. It is a simple two stage transistors preamp that feeds the four diodes double balanced modulator. The carrier frequency comes from a voltage doubler stage that is located after the VFO or variable frequency oscillator , so at the output of the balanced modulator we have a double sideband signal with a very good carrier suppresion. Following the balanced modulator , and built on a separate printed circuit board is the transceiver's linear radio frequency amplifier chain, that uses four transistors in order to achieve an optimum gain distribution per stage. The output transistor is capacity coupled to a very well designed filter network, that works both on transmit and in receive mode. No attempt was made to reduce the size of the rig, and the several circuit boards were interconnected with proper grounding straps in order to reduce the possibility of ground loops, a frequent cause of instability that shows up at any moment, usually at the worst possible moment during an emergency. Transmitter instability is the cause of severe audio distortion that makes reception or the signals very difficult. So we kept this well in mind, considering that the rig was not only aimed at enjoying local and DX typical ham radio contacts,but that it was going to see a lot of service during communications emergencies, when amateur stations are capable of providing vital links at times of total failure of the professional communications systems. Fortunately we have kept the parts count at a very reasonable level, and also after running many tests we created a very special document that shows the prefered values for each component as well as the highest and lowest possible values that may be used. For newcomers to this nice aspect of our hobby , there seems to be some kind of magic to the values specified by circuit designers, something that is a myth that must be properly demythstified , in order to help home brewers to complete many projects. At times I receive requests via radio, or the e-mail asking what can be done to complete a receiver, transmitter or transceiver because a specific carbon half watt resistor value was not available. My answer always has been... please let me see the circuit diagram, and usually I find out that the builder has electronic components, like resistors, of values very near to the one asked for in the circuit diagram. The same happens with other electronic components , like capacitors and coils, but it is a bit more complicated when you don't have at hand a specific transistor or integrated circuit. You should never be stopped by the lack of a specific component as there are many ways to solve the problem. The idea of providing a circuit diagram with the optimum , lower and upper values of resistors and capacitors does help, as well as providing to the prospective builder a list of transistors and integrated circuits equivalents. Yes amigos, we are aiming at a rugged, easy to assemble single band transceiver to be powered from a direct current source between a minimum of eleven volts and a maximum of fifteen volts, so that it can be used in the field with any available twelve volts car or truck battery. ........................ This is Dxers Unlimited's weekend edition and now here is la numero uno,the most popular section of this program according to your e-mail messages , letters and during two way ham radio contacts with CO2KK !!! Today's question came from a listener in Belgium, who picks up our Internet streaming audio from www.rhc.cu between 0500 and 0700 UTC. Amigo Marcel wants to know about what he describes as a "rare , odd looking antenna" that he saw recently . Marcel describes the antenna as a helix a spiral with many turns ...each turn , he says is about 10 centimeters in diameter, and the antenna has two identical helixes connected to a center insulator. Well amigo Marcel , what you saw is one of the many ways antenna engineers attempt to reduce the size, to shrink a half wave dipole antenna so that it will fit into a smaller horizontal space. This type of helically loaded dipole IS NOT, and I emphasize it, IS NOT a broadband antenna... But if properly tuned to the center of the operating band, it can provide excellent results. The big problem with this type of helically wound antenna is how to keep the turns of the helix in good shape and evenly separated from each other. The construction of a properly designed helically wound dipole can be simplified by using a length of insulated tubing as a coil form. The ideal material for the support structure is fluorocarbon plastic, known by the trade name of Teflon...a rather costly material by all standards, but good results can be achieved, amigo Marcel , using polyethylene rigid pipe. Just to give you an idea about how such an antenna can be built without fancy tools and using commonly available materials... A half wave helically wound dipole , resonant at 14.15 megaHertz, that is approximately the center of the 20 meters band, can be made as small as half the size of the standard dipole, and even smaller, although less than half size antennas will not be as efficient. If you are not particularly worried with slight losses, using two pieces of 50 millimeters of two inches diameter PVC pipe, each two meters long, you can assemble an excellent antenna for the favorite amateur radio DX band, that is 20 meters... The two identical lengths of PVC pipe are wound with two millimeters diameter copper wire . You will need to wind about five and a half meters of wire on each pipe section, distributing the spacing of the turns so that they will keep a constant pitch. The antenna is installed at the location where it is going to be used, and then turns are removed one at a time until you achieve the lowest possible standing wave ratio at the center operating frequency..., for example you can make a very good compact antenna tuned to 14.070 kiloHertz that will work very well for the digital communications modes, as well as for CW on 20 meters. A similar small helix or spiral loaded horizontal dipole can be built for frequencies above fourteen megaHertz, but it is not practical to make those antennas for frequencies below 10 megaHertz because of the mechanical problems that you will have to deal with . ........ And now , as always at the end of the program, here is Arnie Coro's Dxers Unlimited 's HF plus low band VHF propagation update and forecast. The Sun is once again going through a period of very low activity, with the daily solar flux not even reaching the 70 units, but there is now a small sunspot active region that belongs to cycle 24... the daily optical sunspot count is 12 and likewise the Earth's geomagnetic field is at a very quiet level. Daytime maximum usable frequencies will not go above 20 megahertz most of the time, but you can expect nice Sporadic E openings with some of them even coinciding in time to make those nice dual hop events that extend the coverage via E skip propagation a lot. Don't forget to send your signal reports,comments about the program and radio hobby related questions to inforhc at enet dot cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba