Radio Habana Cuba: Dxers Unlimited mid-week edition for February 20, 2001
By Arnie Coro, radio amateur CO2KK
Hi amigos, welcome to the mid-week edition of Dxers Unlimited, your favorite radio hobby program on the air and on the web! Yes, you can read our show's scripts on the World Wide Web by visiting Dxers Unlimited's website! Now the headlines...
As the spring equinoctial Dx season is approaching, radio amateur KP4EIT in Puerto Rico is reporting daily 2 meter SSB contacts with stations in Brazil, Argentina and Uruguay... Frequency used: 144.300, and this is obviously a very much enhanced Trans Equatorial Scatter propagation... Another amateur radio contribution to ionospheric research, as no scientist could imagine that signals on frequencies as high as 144.300 megaHertz could be propagated via the Earth's ionosphere.
Item two: YES, absolutely, there are more than 50 different ways you and I can enjoy this wonderful hobby... and among the lowest-cost modes is, as expected, AM medium wave Dxing. Get ready for the nearly in-progress equinoctial AM broadcast band DX season... Due to lower solar activity, this spring equinox will probably generate a lot of interesting DX in the range from 530 to 1700 kiloHertz, and also on the three Tropical Broadcast Bands too!
Item three: Homebrewing radio equipment is a lot of fun; kit building is very close to homebrewing, and it may prove to be a nice approach that makes possible building radios that offer both high performance and are good looking too. But don't try to start kit building with a very complex kit... follow Arnie Coro's advice and go a step at a time... By the way, one of the nicest projects to start with is a simple short wave radio!!!
Stay tuned for more radio hobby related information amigos. Margarita Delgado is the sound engineer and producer, I am Arnie Coro, radio amateur CO2KK, here in Havana back with you in just a few seconds....
This is Radio Havana Cuba, the name of the show is Dxers Unlimited, our twice-weekly radio hobby program with the most up to date HF propagation information... Here is item four of today's edition... Dxers Unlimited's very popular Technical Topics section. Today it will be devoted to a fun transmitter project that started when a neighbor decided to get rid of his old vacuum tube TV set, which I happily accepted as a present and took to my garage.
There, inside last century's nineteen sixties TV set, I found several vacuum tubes that still had their markings very clearly printed on the glass envelope: 12AT7/ECC81 ... a dual 9 pin triode with which I had played a lot in the past. Well, one of the 12AT7s from the old TV ended up in a very simple 15 meter amateur band CW transmitter with which I am having a lot of fun. One half of the 12AT7 is used as an overtone oscillator with a 7 megaHertz crystal, and the other half is the final class C amplifier. Fed with around 150 volts on the plates, the rig delivers a little less than one watt to the antenna at CO2KK on a frequency right at the low end of 15 meters... very near the 21.060 kiloHertz frequency used worldwide by QRP or low power amateur CW operators. The little rig keys very well, and so far my best DX is with a station in Bulgaria, using one of the Assymetric Sloping Dipole antennas here. The rig has a very low parts count -- actually I obtained all the components from the old TV set, except for the quartz crystal, and it's fun to see that the power supply, also a homebrew job, is actually larger and heavier than the 12AT7 transmitter.
A more powerful version of the same circuit can be made using a triode-pentode that the TV set used as its audio driver and audio output stages, and also as the vertical oscillator and vertical output stage. This particular type of vacuum tube should be capable of no less than 3 to 5 watts output, but will require a much higher plate voltage. Nevertheless, this is a nice project, too, especially attractive to newcomers to the amateur radio hobby, as it will cost very little and can go on the air with one of the popular short wave radios that have a BFO or beat frequency oscillator, which is essential for receiving both CW Morse Code and Single Side Band voice signals... If you want to learn more about simple, low cost, easy to build and very reliable QRP or low power amateur radio transmitters using vacuum tubes, just drop me an e-mail to arnie@radiohc.org, or a postcard, VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
You have questions.... do you have any radio hobby related question? Well, just ask, and your answer will come out here at our popular YOU HAVE QUESTIONS, and Arnie tries to answer them! Here is today's question: Arnie Coro, what's the difference between a BOX WIRE LOOP and a FERRITE LOOP antenna? Which one will be the best for chasing DX on the AM broadcast band? Signed: Long-time listener from Toronto.
Well, amigo Bruce, today's technology will allow both antennas to show almost equal performance when they both use high gain low noise pre-amplifiers. A box loop, when very carefully designed and constructed, using Faraday shielding and very good balance, is capable of generating wonderful nulls, in fact, they are so good that I can null a 50 kiloWatt transmitter 15 miles away from my home by almost 70 decibels, a fantastic achievement by all standards. And, by the way, both the BOX WIRE LOOP and the FERRITE LOOP should be built in such a way that they can both be rotated around the compass and also tilted at least through 45 degrees. It is really amazing to witness the tremendous nulls that can be achieved by a proper combination of azimuth and tilting. And for those of you not familiar with AM medium wave band DXing, nulls are vital for the AM band Dxers, as this is about the only way that many new stations can be logged, even when a very strong signal is present on the channel that we are monitoring. So, amigo from Toronto... if you want to experiment with both types of antennas, go ahead and do it! You will learn a lot, but at the end of your experiments, you will realize that a well-built sufficiently long ferrite rod antenna with its associated low noise amplifier will match the typical BOX LOOP under almost any circumstances!!!
This is the mid-week edition of Dxers Unlimited, and yes, we do QSL 100 percent here, as a matter of fact we are just mailing our new 40th Anniversary Radio Havana Cuba QSL card. Send for yours -- just e-mail or Air Mail a signal report, or send it e-mail to arnie@radiohc.org, with some comments about our programming in general and Dxers Unlimited in particular, and don't forget to include your postal mailing address if you send your request via e-mail!
Now item five: An antenna-related question that came in just before I started to type today's script: Arnie, can I use the coaxial cable that is used for computer networking with my radios? Well, as a matter of fact, YES, and my analysis is that you came a across some computer type coaxial cable that is now redundant. Well, the only problem that you may find is that some of those cables were made just for inside use, and they do not have the anti-ultraviolet light exposure protection that coaxial cables made for radio use always have. In other words, your computer type coaxial cable may show signs of cracking after a few weeks of exposure to the Sun's ultraviolet rays... So, your best approach should be to run a test... an experiment to see how the computer cable weathers out... Some of those cables are properly protected against UV radiation, while others are NOT, that's why a simple experiment will tell you if the cable is good enough for external use!
And, don't forget that the BNC type connectors used for the older computer networks are excellent for radio use, too... So, if someone is dismantling a computer network made using coaxial cables in favor of the more modern technologies like twisted pair of fiber optics... by all means get a hold of connectors, T fittings, etc. and to that I may add that older network cards which may be either retired or broken down are an excellent source for female BNC connectors, light emitting diodes and other very useful components for the radio experimenter too!
And now amigos, as always at the end of the show, here is Arnie Coro's Dxers Unlimited's HF plus 6 meters propagation update and forecast... Well solar activity is LOW and it seems like it will remain LOW for the next two to three days. Actual Solar FLux is hovering between 135 and 145 units, still quite nice for the higher high frequency bands to open up for many hours every day... A slight downward shift in the daily MUF is seen now, making the 15 meters amateur band and the 13 meters very attractive for Dxing. The actual number of sunspots was 147 on Tuesday, mostly coming from five sunspot groups, none of which has a particularly complex magnetic configuration. The 3000 kilometer realtime MUF or maximum useable frequency, obtained via actual oblique ionospheric chirp sounders was near 40 megaHertz at around fifteen hundred UTC Tuesday.
For short wave listeners, nighttime reception should continue to be very good from 6 to 12 megaHertz, but due to lower solar activity, the 22 meter or 13.6 megaHertz and the 19 meters or 15.1 megaHertz bands will close much earlier in the evening your local time, even for North to South paths.
I'd like to have you listening next Saturday and Sunday UTC days to the weekend edition of Dxers Unlimited, and if you are already an amateur radio operator, let's have a nice QSO, a two way ham radio contact on 10 meters while it is open... Look for CO2KK at or very near 28.500 megaHertz... and before I forget, this one is a special for 6 meter band operators...be on the lookout for possible Trans Equatorial Propagation coupling to Sporadic E... rare -- yes, possible -- true, and when it does happen, the linked modes provide DX signals that otherwise may never reach you!!! Keep those radios on, explore the higher bands... we are still at solar maximum!
prepared Feb-20-2001; transmitted Feb-22-2001-02:16
Arnie Coro CO2KK
Havana, Cuba
February 20, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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