DXERS UNLIMITED
WEEKEND EDITION
SATURDAY, JUNE 2, 2001
By Arnie Coro CO2KK
Send your comments, questions and ideas to: arnie@radiohc.org
Hi, amigos! You are now listening or reading the weekend edition of your favorite radio hobby show... This is Dxers Unlimited, I am Arnie Coro, your host here at RHC's twice-weekly program entirely,absolutely, devoted to our wonderful hobby, the one you and I may enjoy in more than 50 different ways -- from downloading satellite weather data direct to your computer to building the simplest radio receiver that does not even require a battery to operate. And, of course, there is always the pleasure of listening to international short wave broadcast stations, SWLing, the way many of us started to learn about this wonderful hobby.
Here is item one: Solar activity way down... solar flux may bottom as low as barely above 100 units during this rotation...
Item two: Lots of Sporadic E layer openings... FM band Dxers in Europe, North and Central America and the Caribbean are having a nice time enjoying the very intense E skip openings that started after May 25th. And Canadian radio amateurs have reported the first TA, transatlantic E 's openings of the present season this week...
Item three: Thunderstorm season in full swing, so keep those radios away from antennas, ground connections and power lines when you finish using them... and if, while listening or operating your amateur station, there is the slightest evidence of an approaching thunderstorm, disconnect everything, and get away from the radios, amigo!!!
Item four: Majordomo at rhc.cu is the address that provides access to our exclusive Dxers Unlimited's mailing list that sends you the scripts of this show twice weekly in HTML format, something that also allows to include schematics, drawings, photos and even small audio files... Have paper and pencil or pen at hand, to copy the instructions on how to subscribe to Dxers Unlimited's mailing list... Stay tuned for more radio hobby-related information coming to you from Havana. Margarita Delgado is my sound engineer and producer, I am Arnie Coro back with you in a few seconds amigos!!!
This is the weekend edition of Dxers Unlimited, your favorite radio hobby show...our e-mail address is arnie@radiohc.org, and via Air Mail we can be reached at: Arnie Coro, Radio Havana Cuba, Havana, Cuba...
Now here is item five: Let's visit Arnie Coro's radio and electronics workshop... Today, I'll tell you about intermittent faults, one of the worst things that can happen to radio and other electronic equipment...Sitting here at my workbench is a very nice Chinese-made Type 403 Short Wave Receiver, it was built way back in 1963 and uses vacuum tube technology... The type 403 set tunes from 1.5 to 25 megaHertz, and is an excellent general-purpose receiver. This particular one developed a very troublesome fault: from time to time, the receiver started to make a lot of noise, which made reception impossible... The noise sounded like a very high-pitched hiss, and changing the vacuum tubes one by one did not clear the fault. I then started to check the power supply, disconnecting the filter capacitors and replacing them with new ones, but that did not solve the problem...
Using the oscilloscope, the most useful electronic workshop instrument of them all, I found out that one of the intermediate frequency transformers had developed an intermittent short circuit to ground, but the current limiting resistor to the plate of the intermediate frequency amplifier tube prevented the short circuit from blowing the power supply's fuse... Instead, the one-watt carbon resistor was badly damaged, and that was the cause of the annoying noise.... the resistor was actually burning up every time the radio was switched on. The repair called for replacing the damaged intermediate frequency transformer, and the fried resistor, and just in case, I also replaced the bypass capacitor at the junction between the IF transformer and the decoupling resistor. The type 403 Short Wave Receiver, made in the People's Republic of China in 1963 -- a collector's item -- is now back right next to my desk, where I use it to listen to international short wave broadcast stations while I write....
Remember, every time you have to deal with intermittent faults, be prepared to invest a lot of time, as finding the faulty component or components can be a lengthy process! There are several very practical tips for fault-finding, including the use of a carbon dioxide spray that lowers the temperature of the components abruptly, thus helping to find parts that behave intermittently when their temperature changes. I also keep a variable voltage auto-transformer at the workbench, so that the faulty equipment can be connected to it... By moving the supply voltage up and down, sometimes the fault can be located much more easily! Yes amigos, repairing radios, both old and new is one of the more than 50 ways of enjoying this wonderful hobby, yours and mine: RADIO.
Now item six here at Dxers Unlimited's weekend edition: Converting wall warts into really reliable and regulated power supplies is a very good weekend project... But beware, because there are many very poorly built wall plug DC supplies, or wall warts as they are also known. So, if you really want to upgrade one of them, look for the ones that are better built. A simple visual inspection is what you will need to give it the GO or NO GO decision, in order to add the components needed to turn the wall wart into a useful, well filtered and regulated power supply.
You will usually need to remove the electrolytic filter capacitor and add one or two high-quality and high-capacity electrolytics. Using a typical three-legged integrated circuit voltage regulator will provide up to a maximum of 1.5 amps, but the typical wall wart transformer is seldom capable of providing so much current. Anyway, by adding a new high-capacity electrolytic, the two anti-parasitic oscillation capacitors and the three-legged IC regulator, you will be able to turn the poorly regulated wall wart into an excellent voltage-regulated and short circuit-protected power supply, as the IC regulators provide built in short circuit protection of the so-called fold back type, which is extremely effective. So add this one to your list of weekend radio hobby projects... turning wall wart AC to DC power supplies into modern, high-quality, voltage-regulated and short circuit-protected units, that you can use to provide DC power to many circuits that you would like to build in the future!
This is the weekend edition of Dxers Unlimited... you can send your radio hobby related questions, signal reports, QSL requests and comments about our programming via e-mail directly to me at arnie@radiohc.org or if not yet in cyberspace, send your Air Mail letter or postcard to Arnie Coro, Radio Havana Cuba, Havana, Cuba...
Now here is item seven -- an eyewitness, or shall we say an ear-witness, report of a nice 6 meter band opening. Saturday early morning here in Havana was an excellent example of summer sporadic E propagation... I found several channel 2 TV stations coming in as early as 7 o'clock in the morning, and soon afterward, the 6 meter amateur band was open, with many beacons coming in loud and clear... I monitored the beacon band from 50.000 all the way up to 50.085 kiloHertz and could pick up no less than fifteen different beacons. So, the next logical step was to start calling CQ DX Six meters on 50.125 kHz -- something that, as expected, brought the attention of many 6 meter band Dxers, who obviously had kept their receivers monitoring the calling frequency... An almost 4-hour-long opening followed, during which I had the nice opportunity of saying hello to many old friends like Gene W3ZZ, Dave W5WP, Herman N3DB and other active 6 meter band operators who are all getting ready for next weekend's contest. There are very good chances of more Sporadic E DX openings during the rest of the weekend, and next week usually provides one of the best periods of Sporadic E openings every year although so far, no scientist can tell us why it happens!!!
For those of you who are VHF-UHF and Microwaves enthusiasts, here is the map of the Cuban Archipelago with the GRID LOCATOR SQUARES. This is especially important for the upcoming VHF-UHF-Microwaves Radio Amateur Contests.
Item eight: A short answer to a question sent in by a listener in Bermuda:
Arnie, is it true that the old, obsolete big as a shoebox MFM Hard Disk Drives are a treasure chest of electronic components?
ANSWER: RIGHT! ABSOLUTELY... the old MFM Computer Hard Drives use a lot of discrete components; in other words, they have a low level of integration, so they are an excellent source of high-quality electronic components, including some really nice power field effect transistors! So, if you happen to see some of those old hard drives gathering dust somewhere, just pick them up, open them up, and devote some of your spare time to desoldering the very high-quality parts that the manufacturers of those drives used for making them!
Hope this answers your question, amigo from the friendly island of Bermuda, and keep listening to our 6000 kiloHertz frequency which, according to you and others, delivers such an excellent signal there.... SI, YES, OUI...the old MFM drives may not be useful today, with their limited capacity of maybe 20, 40 or 80 megaBytes, but they are certainly a treasure chest of free parts for your radio-related electronics experiments, amigos!!!
And now, as always at the end of the show, here is Arnie Coro's Dxers Unlimited, free of charge, in the public domain, for your enjoyment, HF Plus 6 meters propagation update and forecast: Solar activity is low and was moving down... BUT, we may see at any time a sudden burst of activity from a small but magnetically highly complex SUNSPOT. Solar flux Saturday morning suddenly jumped upward... so be on the alert for possible disturbances during the next two days... Sporadic E openings are now happening every day, and some stations in Canada and the US East Coast have worked across the Atlantic on the 50 megaHertz band....
For short wave listeners, here is again a special advisory: The 13 meter band is very good during the local morning hours... try some of those European and Middle Eastern stations between 21.470 and 21.700 kiloHertz.
Amigos, don't forget to take a little time and send me a signal report and comments about the show... it is always nice to see that all the efforts involved in making this program are really worthwhile, and it's your correspondence that really tells me how much you like it or not! Send e-mail to arnie@radiohc.org or AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba...
See you at the mid-week edition of the show next Tuesday and Wednesday UTC days...
Prepared 02-Jun-2001; transmitted 04-Jun-2001, 20:14 EDT
Arnie Coro CO2KK
Havana, Cuba
June 2, 2001
Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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