Cuba: Radio Havana Cuba Dxers Unlimited's mid week edition for 9 -10 March 2010

By Arnie Coro

radio amateur CO2KK 

Hi amigos radioaficionados around the world... 

I am your friend in Havana, Arnie Coro, radio amateur CO2KK, now ready to share with you about seventeen minutes of on the air and also on the world wide web streaming audio feed... 

Our first news item... the Sun at a standstill, now three consecutive days without a single sunspot active region... something that some scientists simply did not expected to happen, because they thought that magnetic activity on the Sun's surface was about to produce yet another new active sunspot region... but it simple didn't happen. 

So we are now seeing the solar flux go down to 76 units, and there are no signs of new sunspots forming .

Item two...Many listeners are writing to me about their success stories recycling vacuum tubes recovered from old equipment. The most recent e-mail tells me about how he used a power or mains transformer in place of an audio output transformer for the amplifier he is using as the tail end of his nice REGENERODYNE receiver. 

You can always find mains transformers that you can use for audio output transformers … in actual practice they may be just near to you in the form of the so called "wall-wart" power suplies- one of those usually black plastic covered transformer power supplies that are lying around everywhere. In places where the power line voltage is running at 240 volts like in many countries in Europe.. 

A Wall Wart transformer that provides between 4 and 9 volts AC will fit nicely as the output transformer for many vacuum tubes or valves as they are known in the UK. You just need to do some hacksaw exercise, open up the plastic case and release them from their little plastic coffins.

If you are lucky and find one with a centre-tap ,the last one I opened was like this with a two-diode rectifier) then you can make a nice Push-Pull output stage with a double-triode or perhaps two beam tetrodes. I tell you it is a lot of fun to recycle those Wall Warts transformers and turn them into your vacuum tube receiver's audio output transformer.. 

As you and I know well, the audio quality required for communications is within the range between 300 and 3000 Hertz or cycles per seconds, and in actual practice all those power or mains transformers that I have tested in that role work perfectly well. 

Nick, a ham radio operator from Belgium , with callsign ON4NIC was the friend that suggested this topic, after an e-mail exchange about how difficult it could be to locate an audio output transformer for a vacuum tube radio receiver... 

Item three – a follow up to item two .

It is true that looking around the growing number of discarded electronic equipment one can find many parts, components and hardware items at ZERO cost.

For example, the compact fluorescent lightbulbs that use an electronic signal source to generate the high voltage, are my source of transistors that can be rated at , for example 700 volts collector to emitter voltage and at currents as high as 4 amps !!! Two of them , connected using a very simple, classic, two stage audio amplifier stages, provide enough audio for a pair of headphones, all what is needed to amplify the signal from the output of a solid state regenerative detector..

That is the same audio amplifier circuit is used by AA1TJ , amigo Michael Rainey, to provide the audio for one of his minimalist direct conversion Polyakov detector receivers.

A lesson to be learned by the newcomers to the hobby, is to grab anything that looks like it might have inside "something electronic "... 

For example discarded cellphones happen to have a very nice electret microphone to be used as an external mike with a handie talkie FM transceiver !!! 

And let me add here that several of my friends that have received "talking greetings postcards" have found that they can make a very nice CW Morse code practice oscillator with them too...

FAX machines, early days computers, vacuum tubes TV sets... whenever found , are to be taken to our workshops - but be careful if it is your kitchen table - studied, very carefully dis-assembled and all parts recycled for future use... And don't forget to include the nuts, bolts pressure and star washers … all the hardware items , as well as some perhaps odd looking mechanical elements that one day may form part, for example, of your new radio project dial assembly...

All I can add to Nick's ON4NIC nice comments is that dis-assembling things seems to be a lot easier than assembling them... so the recycling process is a lot less demanding of our brain cortex, and so acts as a very relaxing activity, when you are mentally exhausted and need to do a non brain saturating activity …

Stay tuned for more radio hobby related information, coming to you from sunny Havana, where Tuesday morning at around 10 o'clock in the morning the temperature was 25 degrees Centigrade, with a very nice blue sky … 

I am Arnie Coro , in Havana enjoying the nice weather..

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You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and yes amigos, you can send your radio hobby related questions to inforhc at enet dot cu, again, inforhc at enet dot cu. 

Now here is our next news item of today's program... The growing interest of amateur radio operators in digital communications modes is showing up on the ham bands. 

There are lots of stations using PSK31, the most popular digital mode of them all, as demonstrated by several recent surveys of the activity on the 40 and 20 meters bands. The number of stations using PSK31 is much higher than the number of those using other digital modes, although as of late, OLIVIA and JT65 are gaining a lot of interest due to their excellent weak signal performance that far exceeds that of PSK31. 

If you have a laptop of notebook computer and can fit it with an external microphone... starting to pick up PSK31 ham signals on the 20 meters band is just a couple of hours away.. 

You will need to download one of the several freeware programs that decode and encode PSK31, install it to your computer and just locate your radio receiver right next to the computer, so that the audio coming out of the loudspeaker can be picked up by the computer's microphone... As easy as that... no need to assemble of buy a computer to radio interface... it can be done acoustically, and all I can tell you is that it works quite well, as proven by the many PSK31 , OLIVIA and MFSK16 digital modes contacts made from CO2KK, my amateur radio station.

Amateur radio digital communications continues to develop, and some really amazing results are showing up every day.... demonstrating that our hobby is very much alive and capable of providing emergency communications when professional systems fail , as demonstrated very recently once again during the first several days after the earthquake and tsunami in Chile...

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QSL on the air, QSL on the air, to the many Dxers Unlimited's listeners that sent well wishes after hearing me on the air , making a big effort due to the very sore throat caused by the flu... 

I am a bit better today, but not totally recoverd yet... QSL on the air also to several amigos that have written asking how they can start learning to receive and transmit using the Morse Code.. 

And although nowadays it is not a stumbling block to become a radio amateur in many countries, where , like here in Cuba , a no Morse Code ham radio license is available, it is also quite true that there is a growing interest in learning the art of the dots and dashes, a communications mode that is second to none as regards to the use of resources.

As a matter of fact, many professional users that several years ago decided to quit using CW, are now reconsidering their decision, and in some cases, they have now once again implemented the training of Morse Code radiotelegraphy operators … In the case of amateur radio operators, there are many CW contests every year, making the art of CW very much alive among its growing number of fans.

Item six: Imagine a one meter diameter circle made of RG8 U coaxial cable, supported by a simple PVC pipe cross... Inside it , a smaller 20 centimeters diameter circle made of RG58U coaxial cable... that connects to your radio.

This ultra simple magnetic loop antenna is very effective from 7 megaHertz all the way up to the top end of the 10 meters amateur band... For a receive only version, you can use a standard air space receiving type variable capacitor of a total capacitance value of between 300 and 400 picofarads, but you can also make it work with a smaller capacitor , that will then reduce the lower frequency tuning range.

This is a very easy to homebrew magnetic loop, and in case you want to used for transmitting then you can follow two different approaches … one is to obtain a high voltage rated variable capacitor... something that may prove expensive, especially with the vacuum capacitors required for high power operation, and the other is to use a nice old trick. that relies on the fact that good quality coaxial cables have a lot of capacitance per unit length, and are rated at high voltages. 

A ham who is a very creative person uses different lengths of RG8 coaxial cable to tune his magnetic loop to some very specific frequencies... for example, 14.070, the parking place for PSK31 digital communications mode operators. If he wants to operate on 21.070, the 15 meters band frequency... he then changes the coaxial cable tuning capacitor and PRESTO... he is on the air on 15....

Of course that this is not then a continuosly tuneable antenna system, but it works, and I can assure you that it works very well indeed amigos...

And now just before going QRT, here is our twice weekly HF propagation update and forecast. 

As said at the beginning of the program, solar flux is hovering around 75 to 76 units and there are no sunspots in sight... this is the third day without sunspots, and it looks like a few more may be happening, but this may change if a new active sunspot region shows up. 

Expect nice propagation conditions on the 40 meters amateur band and the 41 meters international broadcast band during your local evening hours... If you are on vacation, retired or work shifts... then daytime propagation will be nice on the frequency range between 12 and 22 megaHertz, with possible 25 to 30 megaHertz openings to the South late in the afternoon local time... 

I Hope to have you all listening to our weekend edition of Dxers Unlimited that will be on the air next Saturday and Sunday UTC... and don't forget to provide your feedback by sending an e-mail to inforhc at enet dot cu, again inforhc at enet.cu... or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba ..

Source: http://bit.ly/cG31Y7

Via Yimber Gaviria, Colombia