RADIO HABANA CUBA
DXERS UNLIMITED
WEEKEND EDITION
SATURDAY, JUNE 23, 2001
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hi amigos! Welcome to the weekend edition of your favorite radio hobby program coming to you from Havana.... It's nice to be able to share with you almost 18 minutes of air time with all radio hobby related information!!!
Here is item one: Solar eclipse happening at almost an optimum moment for scientists... Observations of the Solar Corona from the SOHO satellite and scientific expedition along the solar eclipse path are certainly going to provide science with a lot more knowledge about the Sun's outer atmosphere....
Item two: Finding replacement parts for old and new radios is sometimes quite a challenge, so today I'll give you a few tips on how to keep things working using non-standard replacement components.
Item three: Homebrew radio receivers can be as simple as a crystal set, with just a tuned circuit and a pair of high impedance headphones, and as sophisticated as dual or triple conversion radios, but now there is still one new possibility opening up to homebrewers.... assembling receivers that will use the computer's sound card to do all the signal processing. More about homebrew receivers later in today's edition of Dxers Unlimited, coming to you from Havana... stay tuned for more radio hobby related information coming up in a few seconds... ....
You are listening to the weekend edition of Dxers Unlimited, and here is item two: Finding replacement parts for fixing both old and new radios...
Friday I had a friend visiting my workshop, he was in bad need of an output transformer for a very nice S40B Hallicrafters radio receiver of nineteen fifties vintage... His audio output transformer had failed possibly due to its half century of continuos service in our tropical climate, something I could tell from the green taint that could be seen on the enamelled wire that was connected to the loudspeaker terminals... The primary of the audio output transformer tested open, and that, of course, meant that it must be disassembled and then rewound... But my friend wanted to keep listening to short wave stations when he goes to sleep, as the S40B is his bedside radio... 'Arnie," he asked, "do you happen to have a spare audio output transformer for a 6V6-GT tube?"
"No Radames, I don't happen to have one, but here is a 6.3 volts filament transformer; just test it to be sure the 120 volts primary is OK..."
"Hey, Wait a minute Arnie," Radames said... "that's no audio output, its a filament transformer you are giving me!"
Then, I started laughing and asked him to do some mathematics. "See, Radames... the relation between the primary and the secondary of the 6.3 filament transformer is about a 20 to 1 ratio... Got it?? So the 4 ohm output will be very well matched by the 6.3 volt secondary, and the high impedance vacuum tube plate will see something like 3000 ohms impedance -- not the ideal 5000 ohms to voice coil transformer that you are looking for -- but I can assure you it will work quite well, until you have our good friend Martin rewind the damaged audio transfomer."
By the way, Martin lives right next to our station and is a wonderful transformer winding expert. Well, early Saturday morning I got a phone call from Radames, and he said that his radio was working perfectly with the filament transformer used as an emergency audio output transformer.
Now, this is not the only replacement part that can be improvised... every week I have to help people adapt replacement parts for radios, TV sets, VCR's, computers and even medical and industrial equipment, and let me tell you that many times the replacement parts are better than the original ones. One good example: I always keep a pair of silicon rectifier modular replacements for the popular 5Y3 and 5U4 vacuum tube rectifier tubes... The modules include anti-surge protection, but they must be installed very carefully, because using silicon rectifiers instead of the high vacuum diodes will increase the power supply's output voltage quite a bit, something that can certainly shorten the life of or damage the equipment. That's why substituting components for repair work must always be done very carefully, amigos!
This is the weekend edition of Dxers Unlimited, you can get in touch via e-mail with your radio hobby related questions, just send mail to arnie@radiohc.org. And via Air Mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
Now here is item three, amigos!! The very popular "you have questions, and Arnie tries really hard to always answer them..." Here is today's question that came from a listener in Nigeria:
Arnie, at my town the electricity supply is not very stable, the power line voltage changes abruptly up and down, and I understand that some electronic equipment may be actually damaged by those abrupt voltage changes... The question for you is: What's the best thing to do to deal with this problem, Arnie?
Well, amigo from Nigeria, first of all thanks a lot for the nice report of our 13750 kiloHertz broadcasts in English, French and Portuguese!!! And second, here is the answer to your question... I am sending to you via e-mail the circuit diagram of three easily built AC power protection circuits... One is very, very simple, requiring just a relay and a switch, the second one is a bit more sophisticated, and finally the third circuit is really a very well-designed AC power line monitoring and protection system... The first and simpler circuit will disconnect your equipment as soon as there is an instant power failure... and then it will require manual resetting once power is back to normal. Simple as it is, it has saved a lot of sophisticated equipment that uses microprocessors which simply cannot absorb power line surges, big voltage spikes that last only a few microseconds... long enough to destroy sophisticated integrated circuits forever. The second protection device has a few more features, like three light emitting diodes that show you if the line voltage is normal, low or high... The protection device will disconnect your equipment from the power line at certain voltage levels, again requiring manual (and by the way very safe) resetting, as you reset the protection only after the line voltage is back to normal. The third and much more sophisticated protection device includes an electronic timer, and it tries to reset the power to the equipment after a delay period that you may select, from as short as three minutes to as long as fifteen minutes with the values included in the circuit diagram.
One final bit of advice: Whenever thunderstorms are hovering around, simply disconnect all the equipment and wait patiently until the weather gets back to normal, as there is no really effective protection device that can save you from a power surge caused by lightning striking a power line, even one that is several hundred meters away from your location. So amigo from Nigeria, if you have any doubts after reviewing the three simple AC power line protection devices, just e-mail me again...
And for those of you interested in these simple, easy-to-build AC power line protection circuits, just e-mail me to arnie@radiohc.org, or send a postcard to Arnie Coro, Radio Havana Cuba, Havana, Cuba and I'll be sending you the drawings and text file that explains how to assemble your own protection circuits that can save your valuable radio and electronic equipment from the possible damage caused by operating with low or high AC power line voltages, and also prevent the AC power company resetting of distribution line contactors from sending those terrible voltage spikes into your equipment!!!!
The name of the station is Radio Havana Cuba, and yes amigos, many of us started in this fascinating hobby by listening to international short wave broadcast stations, something we all seem to continue enjoying even after many years... And although the short wave bands today are very different from how they were ten, twenty or thirty years ago, and some stations are just going off the air in favor of FM local distribution or INTERNET audio streaming, the fact is that more than five billion people living in parts of the world with very few phone lines and other infrastructure will certainly continue to listen to short wave broadcasts for many years to come. As a matter of fact, there are two important technological advances coming just around the corner that will improve short wave reception. One is Digital Short Wave radio, which is already under test, and the other is Digital Signal Processing, now in use in several high-end short wave receivers, but which soon may be available to manufacturers at much lower cost in the form of a digital signal processing chipset that, when mass produced, will allow the design of a new breed of short wave receiver for the mass market!
In the meantime, some short wave stations like us, here at Radio Havana Cuba, are broadcasting using the much more energy and spectrum efficient SINGLE SIDE BAND REDUCED CARRIER mode, which provides excellent reception without fading, while using transmitters of much lower power output. Try listening to Radio Havana Cuba's SSB frequencies, check 13660 kiloHertz, 11705 kiloHertz, and 9830 kiloHertz, if your radio receiver is capable of tuning to SSB signals. Monitor those frequencies and send me a signal report and comments about the quality of reception that you are able to achieve using SSB as compared to our standard AM short wave broadcasts, amigos!!!
And now as always at the end of the show, here is Arnie Coro's Dxers Unlimited's exclusive and not copyrighted propagation update and forecast: Solar activity is expected to move slowly down, but Saturday morning's optical observation of the solar disk revealed a bright new area of sunspots just at the edge of the Sun's limb that will be rotating into view by tomorrow... The number of sunspots has stayed above 200 for many days, something scientists did not expect at this stage of the solar cycle. The maximum useable frequency via the F2 layer Saturday morning local time here in Havana was reaching as high as 40 megaHertz for the 3000 kilometer first hop to the South, so later in the day it could probably be even higher, making 6 meter amateur band contacts possible at really long distances like as happened Friday between Portugal and Venezuela. Expect possible high intensity solar flares during the next 24 hours due to the highly complex magnetic structure of one of the sunspot regions...
See you next Tuesday and Wednesday UTC at the mid week edition of Dxers Unlimited, and look for CO2KK on the 20 and 15 meter bands after 0100 UTC amigos. It's always nice to have a two way QSO with Dxers Unlimited's fans who are also amateur radio operators!!!
Arnie Coro CO2KK
Havana, Cuba
June 23, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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