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By Arnie Coro

Radio amateur CO2KK

Hi amigos radioaficionados... I am now inviting you to join me for about seventeen minutes totally devoted to our wonderful hobby, yours and mine : RADIO, the fascinating application of electromagnetic waves from the extreme low frequencies up to the region of the spectrum where radio meets with light waves ! 

Yes, there are more than 85 ways that we are able to have a nice time playing with our radio equipment, from sending our amateur radio station's signals to the Moon and using our natural satellite as a passive reflector, to operating an ultra low power transmitter on the 30 meters ham band and using it to make a two way contact with another station located half way around the world. 

The radio hobby is amazingly complex as seen from the engineering side, and at the same time it can be simplified in order to design barebones equipment that can be assembled at home with simple tools. 

For radio enthusiasts around the world, radio is not limited to voice communications... since the very early days of television TV Dxing, picking up long distance signals became a fascinating aspect of the radio hobby, that just recently has experienced a revival in the form of Digital TV Dxing, that here today is making headlines, as I am adding it as the number 86 way of enjoying the radio hobby. 

Yes amigos, Digital TV signals Dxing is becoming popular now that digital TV broadcasts are on the air in many countries around the world. 
More about our wonderful hobby in a few seconds, when Dxers Unlimited's weekend edition will continue after a short break for station ID. I am your host, Arnie Coro, radio amateur CO2KK , in Havana.
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This is Radio Havana Cuba, the name of the show is Dxers Unlimited, and today's program is on the air when our station is about to celebrate its 49th year on the air amigos. 

On the 16th of April of 1961 Commander in Chief Fidel Castro Ruz addressed our nation on the occasion of the burial of the victims of the air attack by B-26 bombers to the Ciudad Libertad airport in Havana. 

During that speech Fidel told the world that Cuba had a new short wave radio station that was , in fact, broadcasting his speech to the world. A few days later on May first , we began to use the name " Radio Havana Cuba" to identify our station. 

And talking a bit more about those early days of our station, we were running the first two transmitters while others were still been installed, and our antennas were up using electricity company wooden poles because the steel lattice towers had not arrived from Switzerland yet. 

Yes, and this is part of our station's history. 

Our first transmitter to be put on the air was an American made Gates one Kilowatt short wave set using a 4-1000A tetrode final amplifier tube, modulated by two 833's...and it was connected to a half way dipole antenna strung between two power company wooden poles that were about 45 feet high , that is about 13 meters above the ground, a very low height for a 49 meters band dipole antenna by all standards... but as our chief antenna engineer said, those two utility wooden poles allowed us to be on the air . 

Our second transmitter was a brand new Swiss made Brown Boveri 10 kiloWatts rig, that was installed in a provisional building at the Bauta transmitting station site. The beautifully built Brown Boveri was a masterpiece of radio engineering, and we had it on the air in record time from the moment the wooden crates arrived in Bauta . 

The third transmitter was quite a challenge, as never before in Cuba's radio history our engineers and technicians had installed and operated a one hundred kilowatt transmitter. Cuba's most powerful transmitters in 1961 were CMBC Radio Progreso and CMQ , both using AM broadcast equipment made by Westinghouse and running 50 kiloWatts. 

Before the big Brown Boveri 100 kiloWatt transmitter was on the air, Cuba's most powerful ever short wave transmitter was owned and operated by COCO, and it was a 5 kiloWatt rig that went on the air way back in 1937 in a failed attempt to link several AM medium wave transmitters located at different Cuban provinces using the short wave signal sent from Havana and picked up with a radio at the remote sites.

So, putting the 100 kiloWatts Brown Boveri on the air was a historical landmark in Cuban radio history, and the transmitter was up and running just a few days before the Bay of Pigs invasion that began with the 15th of April air attack against three Cuban airports and continued with the landing of a 1500 strong mercenary force that was defeated in less than 72 hours. 

So , on the 16th of April, when Fidel announced that Cuba was broadcasting with its own high power short wave station , we had three transmitters on the air at the same time, the one Kilowatt Gates, and the 10 kiloWatts and 100 kilowatts Brown Boveri's .

A few months later, the Bauta site, located west of the Cuban capital, had on the air two more Brown Boveri's completing the installation of the four transmitters and proceeding to install more and better antennas. 

Si amigos, yes my friends, oui mes amis, I had the unique opportunity, as a very young radio technician to participate in the installation of our station's first transmitters and studio to transmitter UHF links... and today I want to pay tribute to the many Cuban radio engineers, technicians and antenna crews that made possible the installation and operation of Radio Havana Cuba's first transmitting station.

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You are listening to the weekend edition of Dxers Unlimited, and here is now our next radio hobby related item amigos. 

A few days ago I came across a very original magnetic loop antenna made from a short length of a type of coaxial cable used by FM and TV stations , as well as Cable TV distribution sytems and that is known among experts as " hardline". 

This type of low loss coaxial cable was used by several amateur radio operators to make a low cost circular shape loop antenna that can be built at very low cost and it relatively short time. 

A very special feature of this type of magnetic loop is that doesn't require the use of special low loss variable capacitors . The loop is about one meter or a bit more than three feet diameter, and it is supported by means of a thick wall PVC pipe section that keeps the loop in a vertical position. 

Tests using the magnetic loop in a horizontal position were dissapointing to say the least, so it was once again confirmed that this type of antenna must be installed in a vertical position. 

This type of magnetic loop uses a rather unsual matching system to connect it to the 50 ohms coaxial cable , and that is what really makes the difference between this design and the classic ones that require a complex and difficult to adjust matching system.

I made a quick test of the concept using a standard 50 ohms RG213 coaxial cable loop, and it does work, but the losses are much higher than those experienced with the loop made of the thick one inch diameter hardline low loss transmission line.

Experimenting with antennas is a lot of fun, and magnetic loops are so compact, as compared with other antenna types, that makes them very attractive for short wave listeners and radio amateurs that are living at locations where the installation of large size antennas is impossible .

If you want to know more about the hardline large diameter coaxial cable magnetic loop antenna , just send me an e-mail to inforhc at enet dot cu, again inforhc at enet dot cu , and I will send you a small file with information on how to build this low cost and highly effective antenna .


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Ask Arnie... si … YES, ASK ARNIE is the most popular section of this program , according to the e-mail messages, postcards, letters , phone calls and even when I am able to contact with a Dxers Unlimited listener that is also a radio amateur operator. 

ASK Arnie has helped to solve many problems experienced by radio hobby enthusiasts around the world..

Today, I will be answering a question sent by listener Bruno from Croatia... Bruno picks up our English language programs via Internet, but he is now also listening on short wave too. He sent a nice e-mail message asking me about the latest version of the Super Islander amateur radio transceiver, because he wants to build one. 

Well amigo Bruno, the Super Islander Mark IV is now on the air, and results are very encouraging considering that it is a 40 meters band transceiver built using recycled electronic components. 

The Mark IV uses a totally different approach to the receiver design, and it adds two solid state audio filters. 

Amazing as this may sound, some of the electronic components used to make the Super Islander Mark IV transceiver came from the circuit boards of broken or damaged Compact Fluorescent Light Bulbs... and that means that there is virtually an endless supply of those parts. 

Here is now amigo Bruno, and amigos listening to the program at this moment, a brief description of the Super Islander's Mark IV receiver module. 

It starts with a simple resistive signal attenuator that feeds a dual tuned bandpass input filter. 

The filter has a limited bandwidth , chosen so as to limit response to out of band signals... The filter is followed by a cascode transistor radio frequency amplifier stage, that feeds a broadband four diodes product detector. 

Low level audio from the product detector goes to the audio filtering and amplifying module, made with discrete transistors, of which several of them are also recycled from the Compact Fluorescent Light Bulbs circuit boards... 

This version of the Super Islander, the Mark IV , is radically different from any previous ones, as we have now switched over to a totally low cost solid state design , that can be easily reproduced because it uses very common electronic components and straightforward , easy to adjust circuits. 

In our upcoming mid week edition I will describe the VFO, or variable frequency oscillator and the transmitter module of this unique low cost amateur radio transceiver, the Super Islander Mark IV... about the lowest possible cost transceiver that will make possible regular two way ham radio contacts on the 40 meters band using either voice or radiotelegraphy modes.


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And now, as always , when I am here in Havana and can make the solar optical observations plus the monitoring of the HF propagation conditions, here is our exclusive , and not copyrighted , in the public domain short wave bands from 5 to 30 megaHertz propagation update and forecast, that will include also the radio spectrum segment between 30 and 54 megaHertz !!! 

Solar activity during the past week has been at very low levels, with even days with zero sunspot count.... and the solar flux not passing 75 units... 

So, we are once again going through a period when the bands above between 18 and 20 megaHertz remain closed due to the very low ionization levels registered that in turn are caused by the extremely low solar activity. And another bit of bad news... scientists are expecting a high speed stream of solar particles that will impact the upper atmosphere starting on Sunday UTC day, something that will very probably cause a geomagnetic storm. 

Solar cycle 24 continues to be a very dissapointing one for short wave radio listeners and amateur radio operators alike !!! 

Don't forget to send your signal reports and comments about the program amigos ! Send mail to inforhc at enet dot cu or via Air Mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba
(Yimber Gaviria, Colombia)

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