Re: [HCDX] Dxers Unlimited's mid week edition for 16-17 October 2007

["Prof. Arnaldo Coro Antich" <inforhc@xxxxxxx>]

>
>
> 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 arnie@xxxxxx, 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
>
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