> > > Radio Havana Cuba > > Dxers Unlimited's mid week edition 16-17 October 2007 > > By Arnie Coro > > radio amateur CO2KK > > Hi amigos radioaficionados around the world and orbiting the Earth, > because, yes, there are radio amateurs in space at this moment, and > they do communicate with hams using 2 meters band equipment aboard the > International Space Station... I am Arnie Coro , radio amateur CO2KK > , host of this twice weekly program and someone that has had the > unique opportunity of talking to cosmonauts orbiting the Earth... a > unique experience amigos, and one of the more than 81 ways of enjoying > our wonderful radio hobby: space amateur radio communications.... Item > two: zero, zero, zero, one after the other is the result obtained by > Solar Observatories around the world that monitor the number and > characteristics of sunspots... Zero sunspots and a solar microwave > flux of below 70 mean that high frequency bands from 20 megaHertz up > are behaving like VHF bands as regards to ionospheric propagation. > Simply there are not enough free electrons available at the ionosphere > to send short wave signals back to Earth on frequencies above 20 > megaHertz or so for 95 percent of the days... An occasional 15 meters > amateur band opening does happen, and one can pick up an international > broadcast station operating on the adjacent 13 meters band, but those > band openings are very short lived.... We must be patient and wait > until the next solar cycle starts and the daily sunspot number and > solar flux go above no less than 20 for the sunspots and 80 to 90 for > the solar flux , that are the required figures to bring back our much > wanted higher frequency bands amigos... > > Stay tuned for more radio hobby related information, coming to you > from Havana , I'll be back with you in a few seconds , after a short > break... > > ..... > > This is Radio Havana Cuba, the name of the show is Dxers Unlimited, > and yes amigos, we do QSL , we do verify reception reports with > beautiful QSL cards... send your reception reports to [EMAIL PROTECTED], or > VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba... and > here is now item three of the mid week edition of the program. > > Our technical topics section, that is rapidly competing with ASK ARNIE > and the HF plus low band VHF Propagation update and forecast in > listener's popularity... The technical topics today is about the > design criteria for an optimized homebrew receiver, using the lowest > parts count that is still consistent with good overall performance. I > have been working on two such receivers during the past several weeks, > as they will be part of the radio amateurs academy training program > now in progress at my Plaza Radio Club here in Havana, where we have > joined efforts with the nearby Cerro Radio Club to provide training > for the newcomers to the radio amateur hobby that will soon be taking > the ham radio license test, required to own and operate an amateur > radio station. > > Receiver prototype one, is an all solid state design, using locally > available parts and components, and like in the case of receiver > prototype two, that is a hybrid vacuum tubes and transistors radio, no > attempt has been made to miniaturize the sets. A lot of nice open > space where to work with the soldering iron, parts well separated from > each other, and the printed circuit designs using wide strips of > copper for interconnecting the components. This design philosophy > leads to very easy to build by the newcomers radios... receivers that > can be also easily modified to add new features, and the most > important thing of all, these two prototypes provide very good > reception within the frequency range from 500 kiloHertz all the way up > to the 50 megaHertz or 6 meters amateur band. But again, no attempt > was made to provide bandswitching using conventional multiposition > switches to select the tuned circuits, instead a much more up to date > switching arrangement using saturated transistors is used... > > Prototype one, the all solid state receiver, follows a modular design > criteria, that starts with the power supply, the first item that the > newcomer assembles and tests under the supervision of the instructor. > This power supply is based on a locally plentiful power transformer, > and the voltage regulator used can provide up to 2.5 amperes at 13.8 > volts, so that it can also be used, in the future, to power a QRP or > low power amateur radio transmitter. Taking into consideration the > locally available components, this power supply can be considered as a > basic > > building block that the newcomer to the hobby can use both for > operating his receivers and transceivers, as well as for doing a lot > of experiments with different circuits. The power supply can be later > modified to provide variable output voltage, as well as several lower > voltages that may be required for other equipment like a CW keyer > > or an external audio filter. > > The building blocks concept has proven to be a very nice approach, > because during the radio and electronic lessons, we assemble one unit > and test it in front of the class. For example, the input signal > attenuator, bandpass tuneable filter and radio frequency amplifier > module has become the de facto standard to add as an outboard accesory > to portable solid state receivers, that lack adequate input > selectivity. A simple demonstration of the improvement to a Sony > ICF7600 D receiver to which the prototype RF input module was > connected by means of a short length of 50 ohms coaxial cable showed a > great improvement in reception , especially within the frequency range > of 5 to 12 megaHertz, where at this particular > > phase of the solar cycle are the most used . The presence of super > power international broadcast stations is one of the problems that > makes reception difficult with those radio receivers that have a very > poor front end design. And, just to provide a bit more of information, > the use of the basic RF signal attenuator, bandpass tuneable filter > and RF amplifier module with a more sophisticated receiver, also > proved to be worthwhile, because the tendency by designers is to use > fixed tuned input filters that are switched when the bands are > changed, in contrast with my receiver prototype that offers the user > the possibility of having a sharply selective tuneable input filter . > > In an upcoming edition I will be describing the third module of the > solid state receiver prototype, the double balanced broadband mixer > and first local oscillator. > > Now Dxers Unlimited's mid week edition will continue with another > popular section of the program; Antenna Topics, coming up in a few > seconds ... > > .......... > > You are listening to Radio Havana Cuba's twice weekly radio hobby > program, and here is now our Antenna Topics section that today will be > devoted to feedback from listeners that are experimenting with the > double spiral loaded dipoles , following the design ideas of Petlowany > and Tektorian... Spiral end loading of antennas is nothing new at all, > and it has been used by low frequency stations that for obvious > reasons could not make use of the extremely high masts or towers > required to achieve resonance at the quarter wave of a wavelength. > > By adding simple top capacitive loading , the so called UMBRELLA > antennas have made possible rather efficient radiators at frequencies > > as low as the long wave AM broadcast band still used in Europe, Africa > and Asia, but that was never brought into use in the Americas. > > The spiral top loading is a stept further, that adds both capacitive > and inductive loading to the antenna, but that does require a rather > complex mechanical arrangement... But until very recently that type of > loading was not experimented with dipole antennas. The latest version > of these spirals end loaded dipoles is the so called TAK ANTENNA, that > according to its designer is able to achieve a very > > high radiation efficiency with a very short horizontal length .A 40 > meters band TAK Antenna is claimed to have more than 80 percent of the > efficiency of a full size antenna, while requiring only about three > meters of horizontal space for its installation. > > Reviews by top antenna experts are very favorable to both the > Petlowany and TAK spiral end loaded antennas, but there is just one > objetion about their use, and that is that they are narrow band > systems, in other words they provide a reasonable good match at a > center operating frequency, and then if you need to move up or down in > frequency, the standing wave ratio goes up very fast. > > Nevertheless these spiral loaded antennas are an excellent option for > radio amateurs that are very short of space to install their antenna > systems, and are of particular interest at this phase of the solar cycle > > when the higher frequency bands, where smaller antennas can be used, > are absolutely useless due to the extremely low solar activity. > > The basic spiral loaded dipole uses two large diameter wire spirals > that have a bit more than a quarter wavelength of wire wound in about > 7 to 10 turns with proper spacing between turns. The matching is done > on site, on an experimental basis, by moving a feed wire along the > spirals to find the lowest possible standing wave ratio... > > Again these are narrowband antennas, but you can understand how useful > they are, when you realize that a 40 meters band TAK TENNA is less > than three meters long, as compared to the 20 meters length required > by a full size wire dipole !!! > > ....... > > Now here is ASK ARNIE, la numero uno, the most popular section of > Dxers Unlimited according to your e-mail messages, letters , postcards > and phone calls amigos... Today I will be answering a question sent by > listener Claire from Indiana, USA. Claire wants to know why she can't > listen to an otherwise strong and in the clear > > short wave signal when she is using her hair dryer.... and she even > adds that she has borrowed one from a neighbor and exactly the same > > type of buzzing noise erase the short wave station she was listening > to. The answer amiga Claire, is that hair dryers, and blenders, as > well as fish tank pumps, and many other home appliances generate wide > > band radio frequency noise that interferes with short wave reception. > > The hair dryers, kitchen mixers and blenders are particularly noisy > because they use a type of electric motor that use carbon brushes to > > feed electricity to the motor's rotor, and very small sparks jump > across causing the generation of radio frequency energy, exactly as it > was done by the first primitive radio telegraph transmitters, the so > called > > SPARK TRANSMITTERS, that had to be banned because they generated wide > band noise all over the radio frequency spectrum !!! > > ..... > > And now amigos as always at the end of the program when I am here in > Havana, get ready to copy Arnie Coro's HF plus low band VHF > propagation update and forecast.. Solar activity continues at > extremely low levels, with the effective sunspot numer ESN at just > four units Tuesday at 15 hours UTC. The geomagnetic field is also > extremely quiet too, and the maximum useable frequency curve is a very > slow starter after local sunrise, reaching only about 18 to 20 > megaHertz at the best times of the day... According to solar > scientists we will have to wait at least one more year to see a > significant improvement on short wave propagation conditions amigos !!! > > Hope to have you all listening next Saturday and Sunday UTC days > > to the weekend edition of Dxers Unlimited !!! Same time, same short > wave frequencies, same world wide web connection, same satellite feed > you are picking us u > ---[Start Commercial]---------------------
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