Hi amigos radio aficionados around the world and orbiting Planet Earth ...welcome to the weekend edition of Dxers Unlimited, reaching you while the Sun is in a very quiet state, zero sunspots, a blank Sun once again, after a lonely solar cycle 23 sunspot vanished behind at the edge of the solar disk... By the way, this sunspot group , number 983, forms part of cycle 23, something that can be affirmed because of its very near the solar Equator position. So once again we are entering into another period of very, very low solar activity that belongs to the tail end of cycle 23…
Item two: for those of you located at latitudes above 40 degrees North, there are chances of geomagnetic disturbances caused by a high speed solar wind, and it those disturbances do happen, AM medium wave broadcast band Dxing enthusiasts will once again be able to pick some really nice DX stations located South of your location…
Item three: Ionospheric oblique incidence sounders of the type known as chirp sounders, have confirmed that during the extended periods of very low solar activity, the nighttime maximum useable frequency has gone down to around 5 megahertz, yes, you heard it right, 5 megahertz for several hours, something that only happens during extremely low solar activity …
QSL on the air, QSL on the air to Dxers Unlimited´s listeners that have sent e mail messages to arnie at rhc dot cu asking when we are going to see better propagation conditions for the high frequency short wave bands… AND THE ANSWER IS : probably , not before the end of 2008, and if you discuss this topic with some solar experts, they will tell you that the end of cycle 23 is extending much further than any of the many forecasts made during the past two years… So, as the 2008 Northern Hemisphere spring equinox approaches, we will definitely still be experiencing very low solar activity and poor HF propagation conditions…
Stay tuned for more radio hobby related information, coming from Havana, I am Arnie Coro, radio amateur CO2KK, back with you in a few seconds amigos!!!
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You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and here is item five of today’s program… more information about homebrew radios and tips about building them. For the past five or six years, I have been involved in the development of amateur radio transceivers, that is a ham radio station that is self contained in a single package, with some circuits that are shared between the receive and transmit functions. That’s a nice way of saving some components, and these radios are different from transmitter – receiver sets, that have completely self contained receivers and transmitters in the same box.
Transceivers are of course more compact and they offer the advantage of single knob tuning. If your set is a transmitter – receiver, you will have to deal with two tuning knobs, separate tuning for the transmitter’s frequency and the receiver’s frequency… Well, the latest version of my low cost, simple transceiver, is now well under way, with many nice features that include a separate power supply. This new version of the Super Islander single band amateur transceiver is capable of running up to 50 Watts power input to the final amplifier stage, something that I have found to be necessary during this extended period of very low solar activity and poor propagation conditions.
The Super Islander MARK THREE follows the modular construction technique that has proven to be so successful in past projects, as one can test the modules as they are built, and if you want to upgrade a module, it is a very easy task to replace an old one and install the new upgraded module. The Super Islander Mark Three is a very flexible design, something that was necessary so that those who homebrew them may make the best possible use of whatever electronic components they have at hand. As a matter of fact, the Super Islander Mark
Three can best be described as the ultimate in modular construction flexibility, with the design making possible for builders to change modules very easily and test upgrades, while , in case something goes wrong, one can just go back to the previous configuration of the transceiver. Maybe in the not too distant future, a complete kit o the Super Islander Mark Three may be made available by the Cuban Electronic Industry, which is now producing high technology medical diagnostic equipment that is used not only by the Cuban Public Health System, but that is also sold to many countries around the world. The Cuban Electronic Industry has the know how and equipment to produce high quality printed circuits, of the type required for amateur radio equipment, so a transceiver kit produced here in Cuba could be made available at much lower cost than a commercially assembled one…
In the meantime, we continue to test our designs, and I can tell you that the results achieved so far with the receiver section of the Super Islander Mark Three design are very encouraging.
Now here is item six: Our number one most popular section of the program YOU have questions and Arnie answers them… I do receive lots of radio hobby related questions every week that are sent to arnie at rhc. Dot cu, or reach me via air mail postcards and letters sent to Arnie Coro, Radio Havana Cuba, Havana, Cuba…Many are answered immediately from a computer data base, while others require individual answers because of their nature, like the one that came in on Wednesday of this week asking about how one could tell if a transistor could be used as a radio frequency amplifier at some specific band of frequencies.
Well amigo Oliver from Liverpool, England, as a very good friend of mine says, when trying to find if a particular solid state device would work, or won’t work as an amplifier at a specific band of frequencies you have to deal with two options: one try to obtain the original manufacturers information data, and if possible even their original test circuits, and if that is not possible, then just go the long way around and assemble a test jig, that will allow you to actually test the operation of the device under conditions that are as identical as possible as how it will operate when used by your design. Having access, for example, to a sophisticated instrument known as a transistor curve tracer will simplify your work, but there are some nice little tricks of the trade that can be put to very good use… For example,
I have a test jig that uses a quarts crystal overtone oscillator circuit that can operate with crystals of the third and fifth overtone types… A transistor that will oscillate with the one hundred and ten megahertz fifth overtone crystal will certainly be a good amplifier device on frequencies up to around 20 megahertz or so… And my test jig has a very simple power output meter that serves as a very good indicator to show the actual gain of each transistor under test at the specific frequency… It is then very easy to choose the best devices for the most critical applications amigos !!!
There are many homebrew test instruments that will help you a lot Oliver, like a grid dip meter, a simple signal generator, and of course, a high quality digital millimeter that is nowadays an essential test instrument that should be in every radio hobby enthusiast tool box!!!
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Amigos you are listening to the weekend edition of Dxers Unlimited, our twice weekly radio hobby program, here is now item seven… An antenna topic, that is today combined with Ask Arnie, as this second question to be answered here today has to do with antennas. Listener Jennifer from Arkansas , USA, tells me that she lives at a downtown location, where the radio noise level is high. Arnie, she says in her e-mail, I can easily tell the presence of several computers, which are turned off late at night, as the noise level drops everyday like clockwork around midnight… And Jennifer asks what type of antenna can be used to minimize the noise coming from the computers.
Well amiga Jennifer my advice is for you to buy or homebrew a magnetic loop antenna, which according to all the tests that I have done here provides the best option as regards to canceling noise sources that come from a specific location. BUT, let me warn you that if the computers generating the harmful radio interference are located all around you, it is going to be very difficult to cancel the noise. In any case, if you keep using your radio’s telescopic whip, you will notice that the computer generated noise is high, if you switch to an outdoor balanced dipole fed via a balun and coaxial double shielded downlead, the noise will go down, especially if you place the dipole so as to minimize the signal from the noise source, but as I said earlier, a tunable magnetic loop that can be turned around will provide the best possible cancellation of radio frequency noise sources that originate in your immediate vicinity…
Professionally built, remotely tuned magnetic loops capable of operating between 10 and 30 megahertz are available from several manufacturers, similar magnetic loops for the frequency range 3 to 10 megahertz are also available, but they are much more expensive and harder to find… Home brewing a simple receive only magnetic loop is something that the average radio hobby enthusiast can accomplish following the many construction projects available from several Internet websites…After some practice and experiments, I am sure amiga Jennifer that with a few hand tools and thee help of a more experienced short wave listener or radio amateur you can homebrew your magnetic loop and install it so that your reception will improve. I have already sent you several photos and drawings of magnetic loops, just to give you an idea about how they look and how easily the receive only versions can be assembled using readily available materials...
And now amigos, as always at the end of the program here is your friend’s Arnie Coro CO2KK HF propagation update and forecast… Its freely available for distribution , of course… Solar activity again at rock bottom levels, some surprising and not expected Sporadic E events have happened during the past week at a time that according to past records they are much less frequent, so keep a good watch on frequencies above megahertz for signs of short skip that indicate the presence of Sporadic E clouds. Solar flux hovering around 70 units, no sunspots in sight and the high speed solar wind hitting the Earth´s magnetosphere is now slowing up, so the geomagnetic disturbance indicator is now moving back to normal values. See you all at the midweek edition of Dxers Unlimited, on the air Tuesday and Wednesday UTC days, and don’t forget to send an e-mail with your reception report and any radio hobby questions that you may want to ask to me… send mail to arnie@rhc.cu , or VI AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba
