Dxers Unlimited

Dxers Unlimited weekend edition 15-16 February 2003

By Arnie Coro

radio amateur CO2KK

Hi mis amigos radioaficionados around the world ! Welcome to the weekend edition of your favorite radio hobby program, devoted entirely to the more than 68 ways you and I enjoy this wonderful way of optimizing the use of our spare time: RADIO... and here is item one: Latest solar numbers show that this rotation the peak was much lower than the previous one, yet another indication that we are moving fast into the lower part of the cycle... The effective sunspot number is now hovering around 85 , still high enough to provide some nice openings on the higher HF bands, but not at all on 6 meters !!! Item two: IBOC and DRM, the IN BAND ON CHANNEL and the Digital Radio Mondiale digital transmission systems are now competing for the Long Wave, Medium Wave and FM digital broadcasts, but it seems like DRM is going to be the winner for the HF short wave broadcasting applications, although the DRM Consortium has still to learn a bit more about marketing and promotion, as they continue to ask for a fee for the receiving software, even to experimenters that could provide them with valuable data worth many times more than what DRM is asking for the software !!! Item three: Cuban Radio amateurs are participating in the yearly bicycle competition ""La Vuelta a Cuba "" The TOUR OF CUBA, that starts at the eastern tip of the island and continues all the way to the western tip, returning to Havana for the final lap. Ham radio provides excellent two way communications for the Tour of Cuba bicycle competition, and several hundred amateur radio operators participate in what is not only fun , but also an excellent way of training for the handling of emergency traffic... Item five: Minimum parts count circuits continue to fascinate electronic enthusiasts around the world... Take for example the ham radio transceiver built by Enrique, CM2IX , Charlie Mike two India X-ray that uses the same MOSFET output power amplifier as the receiver's product detector... According to him, the rig has provided many nice CW contacts and he is now working on how to improve the audio output when receiving... Another interesting minimum parts count receiver the HF9 published by the British QRP Club's magazine SPRAT is an excellent example of what can be achieved with just a single field effect transistor and a three stage audio amplifier ! Item six: Yes, we will talk today a bit more about antennas, giving details of a simple sloping wire with end loading that works very well when you have a single mast, tower or tree from which to support your radiating wire... And we will also take a tour of Arnie's workshop, to see how things are going there... at the end of the show , our ever popular and pretty useful HF plus 6 meters propagation update and forecast ... Now standby for a few seconds, peak up the tuning as Dxers Unlimited continues ... Margarita Delgado is my sound engineer and producer... I am Arnie Coro in Havana.

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Amigos you are listening to Radio Havana Cuba , coming to you via short wave and via our streaming audio from www.radiohc.cu, now here is item six in detail.... The idea of a single sloping wire , with end loading , is not new. As a matter of fact, my mentor in antenna work, Dr. Jose A Valladares Ph.D. Cuba's top expert in the design and construction of HF antennas, showed me one he had installed about forty years ago at a professional receiving site, and that is still working today... The properties of the sloping wires are unique, and if you load them at the end with an easy to build coil, then even a wire that is relatively short can radiate efficiently... For example, a wire just barely 14 meters long, connected to an easy to build coil I am going to describe right now, will provide a very convenient solution to operate on all bands from 80 meters all the way up to the 10 meter band, requiring only a single mast, tower or tree to support one of the ends, while the other end may end up just one or two meters above the ground. The coil is simply 21 meters of no 16 PVC insulated wire of the type used for wiring up homes , wound on a coil form made from a length of PVC pipe that has an outside diameter of 37 millimeters... But let me add that the coil's diameter is not that critical, as I have used 50 millimeters diameter PVC plumbers pipe for the coil form on two of these antennas that are working very well. For use between 7 megahertz and 29 megahertz, the antenna is fed directly with a length of coaxial cable that is connected to a PI network antenna tuner... The shield of the coaxial cable is connected to a wire that acts as a counterpoise and runs down the supporting structure, and that according to all the tests done should not be shorter than about 7 meters ... For the 80 meter band the antenna is connected differently, as you will need to include a 250 picofarads variable capacitor in series, and you will have to tune it to maximum antenna current with a radio frequency ammeter, or while using a field intensity meter. The sloping loaded wire, or SLW antenna is no match to a full size half wave dipole on 40 meters, but it does compare rather well with the standard reference half wave dipole antenna on the 30, 20, 17, 15 , 12 and 10 meter amateur bands. It is also a nice antenna for receiving international short wave broadcast stations on the 49, 41, 31, 25, 22, 19, 16, 13 and 11 meter bands, so as you see, its really an antenna worth of considering for portable work, or even to be installed at home when you are short of space and can only install a single wire antenna. Again, you will need about 15 meters of antenna wire, typically no 14 or no 12 wire, a length of PVC pipe, 21 meters of number 16 PVC insulated wire to wind the coil, a length of coaxial cable , and another length of wire for the ground radial or counterpoise. If you need more information about the SLW , the Sloping Wire Antenna, just send me an e-mail to arnie@rhc.cu, and VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba.

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You are listening to the weekend edition of Dxers Unlimited, coming to you from Radio Havana Cuba, a 100 percent QSL station since we went on the air with our first one kilowatt Gates transmitter way back during the daily tests we ran in February of 1961 !!! And now let's visit my workshop , where yet another simple receiver project is now coming to an end.

The radio is very simple, uses a single field effect transistor as a regenerative detector, that is provided with a dual tuned bandpass input filter that makes a lot of difference as compared to the classic single tuned regenerative circuit. The audio amplifier section of the receiver is very simple and straightforward , using very common parts . So amigos, let's take a look at it !!! The receiver has a simple, yet effective radio frequency attenuator, that feeds the bandpass dual tuned input filter, then you have the field effect transistor regenerative detector stage, that uses a variable resistor, a potentiometer to control the regeneration. The recovered audio is fed from the source electrode of the FET to the input stage of the audio amplifier that has a lot of gain. The audio section was built using standard components, and we made another version that includes an audio filter to optimize reception of CW Morse Code Signals with one bandwidth and Single Side Band voice signals with another bandwidth. The little radio runs with between 7 and 13 volts DC, and a single 9 volt battery will last a very long time because the current drain is rather small, especially with the simpler audio module... You can see the simple FET plus 3 bipolars regenerative receiver by sending for the .jpg file... Send an e-mail to arnie@rhc.cu and I will send you the computer file with the graphic, that is about 250 kilobytes in size. ...

And now, another circuit under test at my workbench... This is a very simple, yet effective crystal oscillator, that uses two transistors and no tuned circuits. With the values that I determined experimentally the oscillator works with crystals from frequencies as low as 1.8 megahertz all the way up to 20 megahertz . These must be fundamental frequency crystals, and the overtone crystals will oscillate, but not at overtone frequencies, but at a frequency that is approximately a third of the indicated frequency. This circuit has proven to be an excellent choice for building HF converters, as the one I have just finished recently to add the 17 meter band to a radio that only tunes to the classic HF amateur bands.

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Now here is item eight of today's edition of Dxers Unlimited amigos, our popular you have questions and Arnie tries to answer them. Today's question came from no less than fifteen listeners all around the world, and they all want to know which are the most popular amateur bands.... Well amigos, my reply to your question is that according to worldwide statistics, the most used amateur band of them all is TWO METERS, using the FM voice mode, and on the HF bands, 20 meters has the largest number of users, although I may add that not all of them can be described as happy users, as the 20 meter band is really crowded and full of QRM !!!

And now as always at the end of the show, here is Arnie Coro's exclusive and not copyrighted HF plus 6 meters propagation update and forecast... Slight disturbance in progress, especially at higher latitudes, the A index, went up to 20 and should now be going down, solar flux is hovering around 125 units and it is evident that the peak of this rotation has just passed, so expect much lower solar activity during the next two weeks. The effective sunspot number is now around 90 , still high enough to provide nice DX possibilities between 15 and 22 megahertz during your local daylight hours... Very few if any 6 meter band openings will occur , due to the low ionization levels of the F2 layer of the ionosphere... See you all at the mid week edition of the show next Tuesday and Wednesday UTC days, and to all of you that have requested computer files of Dxers Unlimited's radio projects, let me say that I have a small backlog, that I hope to be able to bring to an end this weekend !!! Si amigos, too many requests of happy Dxers Unlimited listeners that are enjoying the hobby now, and want to build those nice little gadgets !!!