RADIO HABANA CUBA
DXERS UNLIMITED
MID-WEEK EDITION
TUESDAY, APRIL 24, 2001
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hi amigos! Welcome to the mid-week edition of Dxers Unlimited, coming to you just a few days before our station will celebrate its 40th Anniversary. I am Arnie Coro, radio amateur CO2KK, your friend here in Havana, and host of this twice weekly radio hobby program, entirely, absolutely, devoted to our wonderful way of using our spare time... yours and mine... RADIO!
And here is item one: I spent Monday afternoon at our Bauta transmitting site, and had a very nice time with the engineers, antenna towers crew, workers and office staff... A group of us from RHC studios went to celebrate the station's birthday together with them... Amazing as it may sound to techno gurus, senior engineer Dictinio Diaz there, one of the founding fathers of Radio Havana Cuba in 1961, showed us the start-up procedure for the daily broadcast to Europe on 11760 kiloHertz, a ritual he has performed now during 40 years of hard work... and I said, amazing as it may sound, because he loaded up the final amplifier stage of the 40-year-old Brown Boveri 100 kiloWatt transmitter to its nominal output power and then, just for fun, showed us how he could even get 10 extra output kiloWatts, an indication of the excellent shape in which the Swiss built transmitter still is, thanks to the loving care provided by Bauta's technical staff. We also saw the tuning-up procedure of the German-built Siemens 30 kiloWatt single side band transmitter, as it started to broadcast to Europe on 13660 kiloHertz.
Yes, we had a nice time together, which came to an end with a little party with a beautiful birthday cake. Radio Havana Cuba's Director General Milagro Hernandez headed our group, while the Ministry of Informatics and Communications, the organization that is in charge of operating our transmitters by means of RADIOCUBA, was represented by engineer Jorge Martinez Abreu, its Director General. This week we will also be attending a seminar devoted to analyzing the future of international broadcasting, which several distinguished guests from several stations will be attending...
Now item two: Have your seat belts ready, as we may see another bumpy week due to expected high solar activity. According to solar scientists, active region 9393, now known during this rotation as region 9433, is very likely to produce big flares in the high end of the M class or even X type flares... This large sunspot region, with a complex magnetic configuration, will be in what researchers describe as a potentially dangerous geoeffective position for most of this week, that meaning that if a big flare erupts from region 9433, we may see a big impact on the Earth's magnetosphere as soon as the ejected particles reach here... So, be on the alert for those elusive moments when a big flare erupts and the tremendously energetic X and ultraviolet rays reach the Earth's upper atmosphere, causing a short wave blackout...
Item three: Our popular "you have questions and Arnie tries to answer them," today dealing with two completely different topics... antennas, and homebrew radios. All this and more, right here, at your favorite spot for the most up-to-date HF propagation updates and forecasts. Margarita Delgado is my sound engineer and producer, stay tuned...
Yes, you have questions, you send them to arnie@radiohc.org, or via Air Mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba, and via e-mail you get really fast replies, while Air Mail replies take longer, of course... Well here is today's number one question, coming from a listener in Wisconsin, USA: Arnie, why are you building those REGENERODYNE receivers using vacuum tubes and not solid state devices? Well amigo, that's a very logical question... and here is the logical answer: The ORIGINAL REGENERODYNE receiver was designed and built using vacuum tubes; as a matter of fact, the first one I ever saw in circuit diagram form used some rather antique vacuum tubes, which could be easily replaced with much more modern ones, something I did in my first radio that, as you see, was not a replica of an ancient circuit, but a receiver that actually worked better than the original one... Now I have two REGENERODYNE prototypes that use modern vacuum tubes, and both work very well indeed; one is designed for the HF region of the radio spectrum, covering from 5 to 30 megaHertz, and the other one is a VHF set, which so far covers from 30 to 60 megaHertz, but to which I plan to add a second front end for tuning all the way up to the two meter amateur band.
By the way, the VHF Regenerodyne is helping me monitor band openings on 6 meters, by spotting point to point and mobile communcations systems that operate just below 50 megaHertz. Well amigo, and to please you, as I always try to do with Dxers Unlimited's listeners, here is the answer to your second question: YES, we are working on a solid state REGENERODYNE, and so far the prototype is looking good... BUT -- and here is something that may or may not be a problem --it seems like the tuneable regenerative detector working from 2 to 4 megaHertz works a lot better when using modern dual gate mosfets, or metal oxide semiconductor field effect transistors... In other words, the dual gate mosfets outperform bipolar transistors in that circuit rather significantly. Designing the audio stages was an easy job, and to make things better, I decided to add a set of audio bandpass filters that help improve the radio's performance.
The most critical part of the solid state regenerodyne is, without doubt, the regenerative detector stage, as the front end is nothing but a standard, run-of-the-mill RF amplifier stage, a passive dual balanced mixer using 4 high performance diodes, and the injection oscillator -- which in the prototype is using a crystal clock module from a dead computer motherboard, running at 8 megaHertz -- so that the experimental radio tunes from 10 to 12 megaHertz, a band of frequencies that is open during practically 24 hours a day, and that allows me to test drive the set on the 30 meter amateur band, check the 10 megaHertz standard station, and tune most of the rather populated 25 meters international broadcast band.
As soon as the prototype is ready, you all can be sure that I'll make the circuit available, and for those of you who have already subscribed to the e-mail distribution list for Dxers Unlimited's scripts, our webmaster has made possible added photos and circuit diagrams to the scripts sent to you automatically which are now in HTML WEB format. You can susbcribe to our e-mail distribution list by sending an e-mail to majordomo@rhc.cu, leave the subject line blank, and in the body of the message type "subscribe dxers_l" We already have quite a few listeners subscribed and it is, according to them, working very well, giving you the chance to read the script at your convenience, even it you could not hear the show on the air....
Now item four: a question sent in by a listener in Mexico; there are several English speaking Mexicans who listen both to Dxers Unlimited in English and to En Contacto in Spanish, where I do a regular HF propagation feature... Another antenna-related question: Arnie, can I replace the aluminium disk on top of the broomstick with something easier to find here? Well amigo, the aluminium 30-centimeter diameter disk is ideal, but you can do well by using no fewer than 8 wire spokes, each 30 centimeters in length. The wire spokes should be carefully soldered to a small ring made of heavy copper wire, like no.12 or no.10, and the ring in turn must serve as the top termination for the wire that makes the BROOMSTICK coil...
BROOMSTICK antennas without the top capacitive loading will work, but they are not very good when transmitting. So, if you plan to use your BROOMSTICK only for receiving, just wind the wire and terminate it on a soldering lug that you will need to attach to the insulating material used as the coil form for winding the BROOMSTICK. By the way, I made a very small BROOMSTICK cut for the 10 meter ham band... it is barely 2 feet, or 60 centimeters, high, but does require the use of no less than 4 and better yet 8, 12 or 16 ground radials that must be no less than an eighth of a wavelength long, and better yet, a bit longer than a quarter wavelength at the operating frequency...
This is Dxers Unlimited's mid-week edition. Solar activity is expected to move to HIGH during the next 24 to 48 hours if it is not already there. Solar flux is hovering near 200 units and a geomagnetic disturbance that sent the A index up to 22 is now subsiding.
Now item five ... Cuban radio amateurs have found yet another source of free electronic components... Guess... can you imagine that a dead compact fluorescent electronic lamp is a goldmine of parts for the experimenter? And although Cuba is now recycling those energy savers when they break down, the ones that cannot be repaired are a nice source of resistors, capacitors, diodes and two medium power high voltage transistors that everyone here seems to be experimenting with... So far, they have proven to be excellent as series pass regulators for power supplies, output stages for audio amplifiers, and experiments continue to try to use them in a transistor RF power amplifier in the 10 to 20 watts class....So add this one to the list: energy saver electronic fluorescent lamps are yet another source of nice parts for experimenting...
And now amigos, as always at the end of the show, here is Arnie Coro's Dxers Unlimited, propagation update and forecast: Solar flux is moving UP, we may see solar flares erupting from active region 9433 pretty soon. Expect much better 10 meter band conditions later today and on Wednesday, if no solar flare erupts in the meantime. Solar flux is now very near 200, and as you all well know by listening to this show, solar flux values higher than 150 usually will make things happen on 10 meters.
For short wave listeners, the best nighttime bands for easy listening are the 22, 25 and 31 meter bands, while daytime reception of international broadcast stations will be at its best on the 13 and 16 meter bands, with 19 meters coming in a close second... Attention 6 meter band operators: be on the lookout for the first sporadic E openings of this summer season; they may start at anytime now...
E-mail me your comments about the show, your radio hobby related questions, and QSL requests too... send them to arnie@radiohc.org, or via Air Mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba...
See you on 10 meters if you already have your own amateur radio station, frequency 28.5, plus or minus 5 kiloHertz, and when 10 is closed, try looking for CO2KK on 20 meters, on 14.2 or very near that frequency.
Prepared 24-Apr-2001; transmitted 25-Apr-2001, 21:00 EDT
Arnie Coro CO2KK
Havana, Cuba
April 24, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
To Arnie Coro's Dxers Unlimited
Back to NY Transfer's RHC main page