Dxers Unlimited´s mid week edition for 6-7 May 2008By Arnie Coro, CO2KK
Hi mis amigos radioaficionados around the world and orbiting the Earth…welcome to the mid week edition of your favorite radio hobby program, the one and only covering at one time or another the more than 83 ways you and I share our spare time enjoying this wonderful hobby: RADIO…
Si amigos, yes my friends, oui mes amis… here at Dxers Unlimited YOU are the center of everything, and that´s why this program has helped many listeners to obtain their radio amateur licenses, so that they could then operate their own ham radio stations… New radio amateurs from the USA, Canada, the UK, France , Germany, Japan, New Zealand, Mexico and Brazil among other nations are now enjoying this wonderful aspect of the radio hobby, after listening for some time to Dxers Unlimited and
becoming then interested in amateur radio.
As many of us did years ago, the newcomers to ham radio started as short wave listeners and they continue to enjoy picking up short wave broadcast stations from around the world ! Item two: HF propagation, still in the doldrums, but there are some good signs of possible improvements in the near future… the emergence of new solar data that shows without any possible mistake that solar cycle 24 is just stretching its legs and about to start with more frequent sunspots …
Solar scientists are keeping track of what´s happening 93 million miles away from Earth by using sophisticated Sun monitoring satellites. One of them under the acronym of SOHO, Solar Orbiting Heliospheric Observatory, has now exceeded its theoretical useful life span, but it is still in such a good shape that scientist believe it will provide very important information about the now starting up solar cycle…
As I have said here many times, amateur radio need not be an expensive hobby at all… It can be enjoyed by people on a shoestring budget, and let me add that sometimes those of us with limited budgets seem to enjoy it even more than those who have the opportunity to buy the most sophisticated and expensive radios and antenna systems… Take for example how just recently a newcomer to amateur radio needed to complete a ham radio station in order to be able to obtain his license.
Here in Cuba you must provide the telecommunications authorities with the block and circuit diagrams of your homebrew transmitters or transceivers, and after they are approved to comply with the spectrum protection regulations, then the radio inspector visits your station and performs a test, before the license is extended. The amateur radio license lasts for a three year period, and it costs 3 cuban pesos and 33 cents per year. Well, back to the new radio amateur, he was in a hurry to complete his station, he already had a nice professional short wave receiver, so in order to obtain his license, he only needed to homebrew a simple transmitter, and here it was when he asked for my help… More about the ultra simple, minimum parts count CW transmitter than resulted from that request in a few seconds, when the midweek edition of Dxers Unlimited continues … I am Arnie Coro, radio amateur CO2KK in Havana…
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This is Radio Havana Cuba, and here we are on our 47^th year on the air. Radio Havana Cuba is has been on the air since 1961, and ever since that first day broadcast all our frequencies have been legally registered by the Cuban Ministry of Communications until the year 2000 and from the year 2000 to this date by the Ministry of Informatics and Communications. Cuba is a member nation of the International Telecommunications Union and registers the use of all of its broadcasting frequencies with the ITU according to the established procedures. And for those ignorant persons that are claiming that membership of the so called HFCC or High Frequency Coordinating Committee is mandatory, let me underscore that the HFCC although recognized by the ITU as a voluntary organization is NOT and I repeat this is NOT in charge of registering the frequency assignments for international broadcasting for all ITU members.
A very easy to do on line consultation, will show up immediately that not all ITU member nations form part of the HFCC, and that the nations that are not members, may register and do register their use of the international short wave or decametric broadcast band frequencies directly with the ITU in Geneva. As a matter of fact the ITU Geneva office runs a complete and detailed international short wave broadcasting compatibility program that is available to all member nations , so it is in fact available for those that form part of the voluntary HFCC group and to those that have chosen for one reason or the other to not become part of the so called HFCC group.
My advise to those who voice out unsubstantiated and wrong opinions about international short wave broadcasting is to learn more first about the coordination procedures set up by the ITU before claiming things about the non membership of nations on the HFCC.
Every broadcasting period, RHC frequencies are properly registered with all the operating parameters requested by the ITU, and that procedure is carried on with the proper advance notification by the Cuban Ministry of Informatics and Communications , that then receives from ITU Geneva the list of how our frequencies were registered and all the possible incompatibilities with other administrations frequency registrations, so that they can be worked out in such a way that better reception of international broadcast stations will result for the listeners.
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You are listening to the mid week edition of Dxers Unlimited and here is now our technical topics section for today… The design, construction and actual on the air testing of an incredibly simple amateur radio CW transmitter that solved a very practical problem for a newcomer to the hobby… because after he finished assembling here at my workshop his ultra simple transmitter and power supply, he was able to obtain his amateur radio license… As I already explained here at the start of the program, Cuban radio amateur regulations prescribe that the person requesting to obtain the license to operate and amateur radio station must show an actual operating station on the air… The station is then inspected and approved for operation, and finally the callsign is issued to the new radio amateur..
So , this new ham, Frank, came in and told me that he had a nice short wave receiver, but no transmitter, and that he wanted to go on the air as soon as possible… I told him that I had a 40 meters band quartz crystal, and several recycled components from broken down energy saver lightbulbs, plus a stock of other electronic components recovered from old TV sets. He was very enthusiastic and ready to wire up his power supply and transmitter immediately.
The first step was to draw the block diagram of the power supply and transmitter… It was clear that we will be using one of the many plentiful locally TV set vacuum tubes that are very rugged and reliable.....
The vacuum tube transmitter required a power supply capable of providing voltage to light up the filaments o the tube or valve and high voltage for the plate and screen grid of the tetrode tube that once served as the horizontal output stage of a black and white TV set.
A power transformer also salvaged from the same black and white TV set provided all the voltages required, and in less than three hours we had a nice power supply providing 6.3 volts AC at up to 5 amperes, and approximately plus 300 volts DC at an incredible half an ampere of current…
We added a glow discharge regulator tube to provide plus 150 volts regulated voltage, and then completed the power supply with a connecting cable that had a wire for the B plus 300 volts, another one for the 150 volts regulated voltage and a wire for the 6.3 volts AC for the filaments, the fourth wire was the common ground. The four wires ended in a plug that was made from a broken down octal vacuum tube.
The power supply was tested using dummy load resistors, and it worked perfectly well from the first moment, so fortunately no wiring errors were mad. We used the nice 1N4007 high voltage silicon rectifiers that were recycled from the energy savers light bulbs electronics, and the electrolytic capacitors came from a retired computer power supply… they have a rated capacity of 330 microfarads at 200 volts DC, that is direct current working voltage, so we simply put two of them in series to obtain an effective capacitance of 165 microfarads at 400 volts DC operating voltage. To complete the power supply we used a filter choke also removed from the TV set, as well as a nice on off switch and a fuse holder.
To add some beauty to our power supply we used a bright red LED to show the presence of high voltage and a green LED to show that the filament was on…For those of you thinking that 300 volts would not be enough for the transmitter, let me say that 300 volts at a plate current of 100 milliamperes will yield a 30 Watts input power, that in our ultra simple transmitter circuit will translate into no less than 10 to 12 Watts output into the antenna system, a power output that is more than enough to be able to work many stations on the 40 meters band…
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After we completed and tested the improvised power supply built from recycled parts, we started to work on the simply one tube transmitter, but always leaving enough space to transform it later into an MOPA transmitter later. That is a Master Oscillator Power Amplifier, as they were known to the old timers… The single tube transmitter we built so that my friend could obtain his ham radio station license uses a TV sweep tube and the crystal oscillator in a simple oscillator circuit, known among the electronic GURUS as an ECO or electron coupled oscillator…
The screen grid acts as the plate of a triode oscillator to which the quartz crystal is connected, and this improves the stability and makes the keying of the oscillator much nicer. We decided to use a classic breadboard layout, and after about three hours, the rig was on the air, bringing in its first QSO … During the weekend edition of the program I will tell you more about this ultra simple transmitter and some of the nice DX we worked despite the poor propagation conditions …
And speaking about propagation, here is a short form HF propagation update and forecast, solar activity at very low baseline levels, with solar flux around 68 to 70 units and a quiet geomagnetic field. So don´t expect much DX on20 meters and above during the next several days amigos.....Send you comments about this program to inforhc at enet dot cu or via Air Mail to Arnie Coro, Radio Havana Cuba,
