Cuba: Dxers Unlimited's mid week edition 19 - 20 October 2010

By Arnie Coro

radio amateur CO2KK

Hi amigos radioaficionados around the world and orbiting planet Earth, because, yes, there are radio amateurs in space at this moment, and they do communicate with hams all around the world, including Cuban stations,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 space travelers orbiting the Earth... a unique experience amigos, and one of the more than 87 ways of enjoying our wonderful radio hobby: space amateur radio communications....

Item two:

more and more sunspots in sight, one after the other is the result obtained by Solar
Observatories around the world that monitor the number and characteristics of sunspots...

More sunspots in sight and a solar microwave flux just passing the 90 units mark mean that high frequency bands from 20 megaHertz up are at last coming back to life. Monday late afternoon I found the 10 meters ham band open to Argentina and Brazil, as well as to Iowa and California... something that came as a most wellcome surprise, and that can be traced to the sustained increase in solar activity of the past few days..

An occasional 15 meters amateur band opening did happened during the past several weeks, and one could pick up international broadcast
stations operating on the adjacent 13 meters band, but those band openings were very short lived....

Now with the daily NOAA sunspot number reaching 69 units on Monday October 18^th, and more sunspots appearing at the edge of the solar disc, I am expecting much better propagation conditions on the 20, 17, 15, 12 and 10 meters amateur bands, and also on the 19, 16 , 13 and 11 meters international shortwave broadcast bands.

Stay tuned for more radio hobby related information, coming to you from
Havana , I am your host Arnie Coro, radio amateur CO2KK back with you in a few seconds , after a short break for a station ID...
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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 inforhc at enet dot cu, 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 possible parts count that is still consistent with good overall performance. I have been working on two such receivers during the past several years and now they are part of the radio amateurs academy training program that is 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.

Among the basic design criteria was to have a lot of nice open space where to work with the soldering iron, that parts should be 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 as solid state switches 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 by the builder in the not too distant 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.

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 .

Now Dxers Unlimited's mid week edition will continue with another popular section of the program; Antenna Topics, coming up in a few
seconds ...
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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. But be aware that antenna modeling software clearly show that most of the radiation is actually coming from the coaxial cable feeder connecting the TAK TENNA to the transceiver !!!
….......

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 Amanda from Oregon, USA. Amanda 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.

Hair dryers, kitchen mixers and blenders are particularly noisy because they have 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 !!!

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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..
( updated at the very last minute when the show is going to be recorded)

Hope to have you all listening next Sunday and Monday UTC days to the weekend edition of Dxers Unlimited !!!

Source:Dxers Unlimited's mid week edition 19 - 20 October 2010 http://bit.ly/bKC5JN

(Yimber Gaviria, Colombia)