RADIO HABANA CUBA
DXERS UNLIMITED
MID-WEEK EDITION
TUESDAY, JUNE 26, 2001
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hi amigos, once again you are most welcome to Dxers Unlimited, your favorite listener-oriented radio hobby program, coming to you via short wave, and also available for reading at our Dxers Unlimited website ... I am Arnie Coro, radio amateur CO2KK, your friend here in Havana and host of this twice-weekly program.
Here is item one: Solar flux and the number of sunspots started to move down, after a very interesting period of sustained activity... but, beware -- there is one solar sunspot active region with a complex twisted magnetic configuration from which a powerful solar flare may erupt at any moment during the next three to five days...
Item two: Ionospheric absorption of radio waves during local daytime hours and an expanding ionosphere are making daytime HF propagation rather poor, but things do change after local sunset....
Item three: More about vintage radios and how oldtimers' construction techniques may be reproduced to enjoy some really nice performing circuits...
Item four: Don't throw away that MS DOS computer, amigo! There is a very nice freeware computer program that, with a very simple interface will turn your old machine into a wonderful multi-digital modes terminal that will work with any digital radio signals... and MIX 2.21 will also allow you to transmit, if you already happen to be the happy owner of an amateur radio station. More about MIX 2.21 later in today's edition of Dxers Unlimited, coming to you from Havana.
Item five: Feedback from our worldwide audience... Every edition of the show seems to bring into our wonderful and fascinating hobby casual short wave listeners who just happened to be tuning around the bands and find the show quite by chance. And, as expected, they want to learn more about radio!!!
Stay tuned right on this same frequency as this program is designed for both beginners and experts... I'll be back with more radio hobby related items in a few seconds...
The 386 machine was sitting dormant inside a closet at a friend's home... I saw it quite by chance, when he opened the door to retrieve some electronic components in storage there.
"What's that?" I asked Pedro, and he said... "It's a 386 DOS machine, with a 33 mHz CPU, Arnie."
"Hey, amigo! You can add several digital modes to your ham station with that machine, you know..."
Then Pedro asked how it could be done, as the 386 had no sound card...
"Well, amigo Pedro, there is a ham radio software freeware program by the name of MIX version 2.21 that lets you work a number of digital modes using a very simple interface between the computer and the radio... It's the ever-popular HAM COM interface, and MIX has the advantage over the HAM COM program that it does operate PACTOR, the hybrid mode that makes possible actual links between digital stations..."
It took us about an hour to gather all the parts needed to build the interface, and Pedro then went with me to my home, as the DB25 connector needed was not among the parts he kept in his very well organized junk box...
A day later, Pedro called me to say that he was already receiving Morse Code CW signals on the 40 meter band, but that reception was not very good, probably due to the lack of appropriate selectivity in the receiver he was using... I helped him to start monitoring the RTTY, or radioteletype, sub-band between 14.080 and 14.100, and he was then able to pick up several two-way QSO's....
"It works!" he said, "Now let's try PACTOR," something that took just a few more minutes of familiarization with the software.
MIX, by the way, is a rather small program, it is available in ZIP format, and by running a search on the INTERNET you will be able to find the nearest FTP site where it can be downloaded.
The 386 MS DOS machine running at 33 mHz with an old CGA monitor is handling the MIX software like a champ, and my friend Pedro has already made many ham radio digital modes contacts using this simple set-up.
"Arnie," he said on the 2 meter repeater yesterday, "I could not imagine that I had an almost complete digital ham station right here at home... Thanks for telling me about MIX!!!"
You can download MIX for DOS right here on our Dxers Unlimited website. Again, you can start monitoring digital modes, at least some of them using an old desktop or laptop machine, it won't need a lot of memory and the monitor can be CGA or VGA monochrome, no need for fancy stuff with MIX, and later, with 486 type machines you can start thinking about running some of the freeware that uses 16 bit soundcards to decode digital modes, something that will require an even simpler computer to radio interface...
Remember amigos, older computers can be put to work very effectively using many MS-DOS very well written programs that are available for downloading free of charge from many websites!!!!
You are listening to the mid-week edition of your favorite listener-oriented radio hobby program, this is Dxers Unlimited and here is our feature dealing with vintage radio's technology.... It uses just two vacuum tubes, they are both operated at rather low plate voltage; it's my favorite bedside radio, the one that I keep on all the time when monitoring the bands. My simple regenerative receiver tunes from 3.5 to just above 10 megaHertz, it has just one set of hand wound coils and no bandswitch... And let me tell you, amigos. that this was the prototype of what has become now a very popular beginner's receiver. Parts for building it are plentiful... and the reliability of the circuits used in my design is outstanding, to say the least... As a matter of fact, this radio, built some fifteen years ago, has never seen a part replaced...It uses a dual triode that works as an RF untuned isolation amplifier and regenerative detector... and a triode pentode dual tube that works as the audio pre-amplifier and output stage. It runs from a very simple power supply that was made using two 6.3 filament transformers so as to provide 115 volts AC isolated from the power line. In other words, the power supply is as simple as you can think, just a half wave rectifier using a silicon diode, two ex-computer 250 volts DC electrolytic capacitors and a filter choke that I removed from a 1950's TV set. I added a 75 volts gaseous discharge voltage regulator tube, but this isn't really needed, although it does help to improve the receiver's stability... The parts count is as low as you can imagine, as I took a lot of time thinking how simple this radio could be...
The homebrew 12AT7-ECL-85 receiver is an excellent explorer and provides good reception on the 60, 49, 41 and 31 meters broadcast bands, plus reception of amateur signals on 80,40 and 30 meters, with good bandspread. Calibration is not that good, though.... but there is nothing like a well-trained listener, as many of you know by now, and for me, it is easy to find Radio Australia's 9580 kiloHertz during my early morning here in Havana, check WWV on 5 and 10 megaHertz, pick up Radio Rebelde's 5025 Tropical Band outlet, and check the calibration by tuning to our own Radio Havana Cuba's 6000 kiloHertz morning magazine show in Spanish.... The two tube plus one silicon rectifier regenerative receiver was built using just recycled parts... The two variable capacitors came from an old radio and a dead FM tuner... one is used as the bandset, and the other provides a nice bandspread.... The two tube regenerative receiver was built to last, and no attempt was made to make it a miniature radio. Parts were placed well spaced from each other, so that soldering them would be easy... The front panel was made from a piece of steel plate, something that I always recommend to those who want to build regenerative receivers, as the shielding provided by the steel plate panel stops the hand tuning capacity effect so typical of those radios when not equipped with a well-shielded front panel.
The two tube regenerative was built backwards, that is, first the power supply was assembled and tested, then the audio amplifier stages were built and tested, and finally the regenerative detector and untuned isolating stage were assembled. This way of assembling nostalgia radios will avoid the need for fault-finding once the receiver is finished, as only the detector stage has to be tested when it completely wired. My advice for those interested in building this simple receiver is to first gather all the components, spend time in testing each and every part, do the layout of the circuit providing enough space between parts, mount all the parts that need to be installed to the chassis like tube and coil sockets, variable capacitors, the front panel etc, and then proceed to do the actual wiring, starting as I said from the power supply. Test the supply after wiring it, and then proceed following a step-by-step process to wire the rest of the radio...
The circuit diagram for this simple two tube radio receiver is available in an easy-to-see .jpg format, and I will be very happy to send it to you via e-mail. Send your request for the two tube regenerative receiver to arnie@radiohc.org and in case you do not have e-mail available, just drop me an AIR MAIL postcard to Arnie Coro, Radio Havana Cuba, and I'll be very happy to send it to you VIA AIR MAIL, too...
Arnie Coro's Two tubes plus one diode radio receiver is a FUN PROJECT that will bring in many hours of nice listening and later on, you can add my simple crystal controlled converter to turn this two tube plus one diode radio into a very sensitive REGENERODYNE RECEIVER!!!! So you are actually building first the TAIL END of a REGENERODYNE, amigos!!!!
And now, as always, at the end of the show, ready to copy! Here is Arnie Coro's exclusive and not copyrighted HF plus 6 meter band propagation update and forecast: Summer solstice propagation conditions continue in our Northern Hemisphere... Solar flux is now expected to start going down during the next 7 to 10 days, but beware: There is an active sunspot region from where highly energetic solar flares may erupt during the next three to five days, as it crosses along the solar disk. The number of Sporadic E events may increase during the next three to five days, due to yet another meteor shower that is expected to impact upon the Earth's atmosphere.
The best bands for daytime shortwave listening after the Sun is out at your location are the 19, 16 and 13 meter bands...and after your local sunset, the 19, 22 and 25 meter bands will provide the best reception, with the 31 meter band a good second choice.
Amateur radio operators will enjoy nice two way contacts on the 20 meter band almost all the way from local sunset to sunrise...See you at the weekend edition of the show, amigos, and don't forget to send your signal reports, comments about the show and radio hobby related questions directly to my e-mail account at arnie@radiohc.org!
Arnie Coro CO2KK
Havana, Cuba
June 26, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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