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Dxers Unlimited weekend editionsby Prof. Arnaldo Coro Antichradio amateur CO2KKRadio Habana Cuba
Radio Havana Cuba Hi amigos radioaficionados... here we are again giving you a warm welcome from Havana to our twice weekly radio show's mid week edition... I am your host Arnie Coro, radio amateur CO2KK, and here is item one of today's program... Solar activity is at very low level, and an all quiet alert has been launched by scientists that monitor the Sun. So, expect the daytime maximum useable frequency curve to once again show a very slow rise and that it would not reach frequencies above 20 megaHertz even during the peak periods... We will also see lower ionospheric absorption and that will enhance propagation on lower frequencies.... Item two : I have received many requests for the complete detailed list of the many ways that you and I are able to enjoy our wonderful radio hobby... at the latest count there are 86 different options readily available... that range from AM broadcast band Dxing , using whatever radio receiver is at hand , a certainly low cost and available to everyone option, to the super sophisticated microwaves Earth Moon Earth amateur radio communication, that requires extremely low noise receivers and high power transmitters, plus a large diameter parabolic reflector antenna. Add to the list such fine ways of having a good time playing with our radios, participating in amateur radio contests, or perhaps organizing a DX expedition to a remove spot that very rarely is heard on the air... If I keep up adding other ways of playing with our radios, maybe I should describe the fantastic moment that turning on the power switch of a just finished homebrew radio will bring, when you start picking up signals if what you have built is a receiver, or can make a two way contact on the ham bands if the homebrew project is a transmitter or transceiver... The number of ways that we can all enjoy the radio hobby is in my opinion what makes it unique... there is always something new to be learned, a challenge to be dealt with, and not only from a technical point of view, because the very moment that a radio amateur operator helps to save the life of people aboard a boat that is drifting powerless in heavy seas, is a once in a lifetime experience that I always share with every amateur radio license training class at my radio club... Si amigos, yes my friends , oui mes amis...radio is an extremely nice hobby that makes possible to learn many skills, and as a matter of fact quite a large number of people have started a lifetime career in telecommunications and electronics after becoming a radio hobby enthusiast... Item three: Recycling old and not so old but still obsolete electronic equipment provides you with a large number of zero cost electronic and mechanical parts that can be used in many homebrew project. Many years ago I ran across a retired diathermy machine... that looked like it was part of the set used for Flash Gordon episodes... The diathermy machines were used by doctors to treat many different pathologies... by the use of dielectric heating... in other words, a high power radio transmitter was connected to a pair of electrodes, instead than to an antenna... The physician then placed the electrodes in the area that he wanted to be heated by the radio frequency energy, and connected the high power oscillator that was usually tuned around 26 or 27 megaHertz... The diathermy machine that was given to me by the widow of a famous doctor had a pair of 812 type triodes in a self excited oscillator... The tubes ran with raw alternating current on the plates, and grid dipping the plate tank circuit, it was clear that the operating frequency was intended to be around the 11 meters band assigned for industrial and medical equipment... When the diathermy machine was switched on for the first time, with the electrodes placed above and below a wooden log to act as a load, my home TV set went on the blink, and a horrendous sound came out of its big loudspeaker...Now that I was sure that the diathermy machine was working OK, it was the right time to take it apart and recycle the big power transformer, the 812 tubes and their sockets, as well as a beautifully build Cardwell split stator variable capacitor... A few months later the two 812 RCA tubes were providing power on the 40 meters band as the tail end of my second double side band rig … It was necessary to add two big oil filled filter capacitors, and a filter choke, a relay, a filament transformer for the pair of 866A mercury vapor rectifiers and it took a whole weekend to wire the 500 Watts grounded grid linear amplifier that was build using many of the parts recycled from the diathermy dielectric heating machine !!! Stay tuned for for radio hobby information, and some fine radio
history anecdotes too... I am Arnie Coro, in Havana... ….................... Si amigos, sure, this is Radio Havana Cuba, and yes, we had a transmitter breakdown Sunday evening, that kept the 6050 kiloHertz frequency off the air , but the fault was located, properly repaired, the transmitter was tested and it is now once again on the air at full power, beaming to the central area of North America... Actually we call that antenna the “Chicago beam ” , because its azimuth is almost exactly beaming to the Great Lakes region... It is running 100 kiloWatts using a pulse step modulated energy efficient transmitter, and the antenna in used is a classic curtain array, described by the ITU as a 4 , 4 , 0,8 antenna system... This designator explains that it has 4 dipoles on each row, and 4 vertically stacked rows of dipoles, so it could also be called a sixteen dipoles antenna system. The estimated gain over a single half wave dipole theoretically located at the center of the array varies from 5.6 to 12. 6 megaHertz, that is the frequency range where the antenna can be operated. By the way, the sixteen broadband dipoles are placed in front of a huge wires reflector system that gives this type of antenna an extremely high front to back ratio... in other words, the relation between the power delivered in the direction of the antenna beam and the power that is transmitted in the opposite direction is extremely high. This parameter is known among antenna experts as the “ front to back ratio” , and in the case of the 4, 4, 0, 8 curtain array it can easily reach up to a thousand times, or 30 decibels of front to back ratio... Just to give you an idea , when fed with 100 kiloWatts , this type of curtain array operating around 6 megaHertz that has a measured forward gain of no less than 16 decibels over a half wave dipole , will radiate an effective radiated power of around four megaWatts or four million Watts... the backward lobe will then be radiating no less than 27 decibels less... or around 8 kiloWatts. The use of highly directional high gain curtain arrays with such effective front to back ratios is what makes possible to operate more stations on the crowded short wave broadcast bands... ….................................... Amigos, if you have any radio hobby related question, don't hesitate and send an e-mail to me … I read the e-mail messages at least twice daily and answer the questions submitted to Dxers Unlimited as soon as possible... sending them directly to you … and also many times putting both the question and the answer on the air for the benefit of other Dxers Unlimited's listeners... Here is today's question sent to inforhc at enet dot cu.... Amiga Lucy from Vancouver , Canada sent this question to the ASK ARNIE section of this program... "Arnie, sometimes when it is snowing my short wave radio becomes very noisy, and the noise vanishes when the snowfall is over... Any idea of why this happens ? " Well amiga Lucy , this is what is known as precipitation static, and also happens when it is raining hard. The snowflakes pick up electrical charge as they move from the clouds to ground and the discharges of that static electricity is what causes the popping noises !!! Sorry, but there is no known remedy for rain or snow precipitation static noise, and I must add that all radio noise limiters that I have tried out for suppresing rain precipitation static have proven to totally fail, or only bring slightly better reception. There are also other forms of static electricity discharging and interfering with short wave radio reception, for example when a nearby thunderstorm cloud is fully charged and starts leaking those charges to ground or into another cloud of opposite polarity... And now amigos , as always at the end of the show, here is Arnie Coro's Dxers Unlimited's HF plus low band VHF propagation update. Solar activity at very low levels, solar flux at around 73 to 75 units, and an all quiet alert was in progress when I was writing the script of this program Tuesday morning my local time , at half past ten in the morning, that is fifteen hours and thirty minutes UTC or Universal Time Coordinated... The upcoming winter solstice Sporadic E season is still about 10 days away, and my advice is to keep a close watch as this may prove to be an excellent sporadic E skip DX season... 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
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