Radio Habana Cuba: Dxers Unlimited Midweek Edition, 17 August, 1999
By Arnie Coro, radio amateur CO2KK
Hi amigos! Welcome to the mid-week edition of Dxers Unlimited, your favorite radio hobby show on shortwave... I am Arnie Coro, radio amateur CO2KK, and it is my pleasure to share with you the next sixteen minutes of ALL RADIO HOBBY related information...
Here is item one: Geomagnetic storm started August 16th at 1000 UTC; it had a positive phase with generally enhanced short wave propagation, which in a few hours time disappeared and gave way to very disturbed propagation conditions. The A index -- that's the geomagnetic disturbance indicator -- for August 16 went up to 29 units, and at higher latitudes it was much higher, of course. SO... no, your radio was not out of order when you tried to tune to some of your regular stations on short wave... The geomagnetic storm was to be blamed for the poor conditions. But as always, what may be bad for regular professional users of the short wave bands, proves to be a unique opportunity for radio hobbyists to tune to some rare and unusual DX stations. According to the characteristics of the impact of particles into the Earth's magnetosphere, this geomagnetic storm may last for one or two more days. Then, if no more streams of charged particles from the solar corona hit the Earth's magnetosphere, we will enjoy a period of excellent short wave propagation.
Item two: One of the world's leading manufacturers of short wave radios, YAESU of Japan, is apparently moving away from the market. News from Japan says that YAESU's new owners are not interested in development and production of HF receivers. As many of you will remember the FRG7, or FROG7 as it was known, started a new generation of short wave receivers that gave hobbyists their first opportunity to enjoy a receiver designed and built with a "little extra" in mind, as compared with the regular solid state short wave radios available at that time.
Item three: Talking about short wave radios, still another home brew design using a two diode product detector, one transistor, one integrated circuit audio amplifier, and a crystal controlled local oscillator using an integrated circuit will soon be available for downloading at our website www.radiohc.org. The new design, now under final tests at my workbench, is using an exactly 6000 kiloHertz crystal that was given to me by a friend. It brings in the 6000 kHz Radio Havana Cuba transmissions loud and clear. Yes amigos, another little experimental circuit for you to enjoy, coming up soon... Now please stay tuned for more radio hobby related items that will follow in a few seconds. My sound engineer and producer is Margarita Delgado... I am Arnie Coro, radio amateur CO2KK.
Send your comments about the show and the webpage to arnie@radiohc.org -- very easy to remember! Aand via AIR MAIL, drop me a postcard to Arnie Coro, Radio Havana Cuba, Havana Cuba.
Now, straight to item four: A very easy-to-build antenna tuner, that helps a lot when you are using a random length of wire for an antenna... This one does need a ferrite rod, and two variable capacitors of anywhere between 300 and 400 picofarads maximum capacitance. The tuner is so simple to build that you will be surprised with the excellent results!
You are listening to Dxers Unlimited, a radio hobby program that's on the air twice weekly for your enjoyment, the only radio hobby show on short wave that offers a really up-to-date HF propagation updated and forecast. You can receive our beautiful QSL card just by sending a simple signal report and some comments about the show to Arnie Coro, Radio Havana Cuba, Havana Cuba, or via e-mail to: arnie@radiohc.orgArnie's Easy-to-Build Antenna Tuner Parts List: Again here is the list of materials: one ferrite rod, of the ones that are cylindrical in shape, and of a length of about 4 inches or more. You will also need two identical variable capacitors. I prefer using air spaced variables taken from defunct old vaccuum tube radios, the ones you can still find at junkyards and garage sales. If you see vaccuum tubes inside, buy them, as each radio has a very nice air spaced variable capacitor. You will also need about 1 meter (3 feet) of standard, plastic-insulated wire.
Assembly: The tuner is made in the following way: First, you cover the ferrite rod with one layer of vinyl plastic electrician's tape. Then, you wind 10 turns of the plastic insulated speaker wire, spaced one turn diameter from each other. Connect the stator plates of the variable capacitors -- those are the fixed ones -- to each end of the wire, and connect the two capacitors' rotor plates -- the movables ones -- to each other and to your radio's ground connection. Now connect the antenna to one side of the ferrite rod coil where it is joins one of the capacitors' fixed plates. The other identical side goes to the radio's antenna input. And... you have a very nice, easy-to-build PI network antenna tuner! Tune your receiver to the 49 meter or 6 megaHertz band, look for a weak station, and then slowly turn first one capacitor, and then the other for maximum signal. That's it!
Variations: You may want to experiment -- remember that the radio hobby is an experimental one -- and wind more turns, say about 20 tightly wound, and see if you get improved reception at lower frequencies. With a standard 4-inch rod and 15 turns, using two 365 picofarad surplus variable capacitors, my low-cost PI antenna tuner will provide a good match between about 5.5 and 29 megahertz. Remember that the lower the frequency, the more capacitance you will need; in other words, the tuner will reach resonance with the capacitors' plates fully meshed into the fixed plates. Higher frequencies will tune with the capacitor plates out, with the maximum frequency reached when the two capacitors' plates are fully out.
I added a little five-position, single-pole switch and made taps to the coil in a later model. So, if you can get hold of a similar 4, 5 or 6 or even 10-position switch, you can add this feature to make a still-more-flexible antenna tuner. This simple tuner helps reduce image frequencies that are a problem with less expensive radios, and it also stops some intermodulation problems that make reception difficult in those receivers, too... I have used my prototype with a little amateur radio QRP 10-watt single-sideband phone rig with excellent results, as well. And, as always, if reception was not very good, just cybersurf to www.radiohc.org, click to Dxers Unlimited's page, and download today's script, where you can read the complete description of the circuit. You can also learn more about PI network antenna tuners by visiting your library and looking at the antennas chapters of any radio handbook.
Here now is item five: You have questions and Arnie Coro has the answers! Today's question has been sent in by many Dxers Unlimited fans. "Arnie, why does my little portable radio overload very badly when connected to an external antenna?" ANSWER: Because your small short wave portable was NOT DESIGNED to work with an external antenna system. The engineers who design those radios assume that you are going to use them ONLY with the built-in telescopic whip antennas. Those little radios are simply NOT CAPABLE of handling the high signal levels that will go into their input stages when connected to an external antenna system. There is a practical solution to the problem. And that's none other than introducing a very simple resistive attenuator between the external antenna and the little radio's telescopic whip... because, as you may soon realize, most of those very small short wave portables DO NOT, and I repeat DO NOT, have provision for an external antenna connection, something that gives you a very good hint that the engineers who designed the radio did not think of the possibility of using an external antenna. Hope this answers the question! And so, if you are in the market for a somewhat better short wave radio, stay away from those receivers that do not have a plug for an external antenna connection!!!
And now amigos, just before going QRT, here is Arnie Coro's propagation update and forecast: As soon as the geomagnetic storm is over, something you can learn by monitoring WWV at the 18th minute and writing down the K index figure, conditions will actually improve. When the K index drops below 3, conditions will be a lot better. The solar flux will continue to move UP, reaching an estimated 200-plus units by the end of the month. As the number of hours of daylight continue to slowly move down, conditions will become better and better, peaking by the second half of September. But right now, reception is very good on the 21 megaHertz or 13 meter international broadcast band during the daytime, and also very good on the 17.5 to 18 megaHertz band -- that's 16 meters. Due to the contraction of the ionosphere after sunset, you will find 19 meters -- that is 15 to 15.7 megaHertz -- EXCELLENT for armchair reception until midnight and even later; I am receiving quite a few European stations here in Havana just at daybreak in Europe, which is roughly midnight here. For amateur radio operators, here is my advice: call CQ a lot on both 15 and 10 meters, even on what may sound like a "DEAD" band; you will be pleasently surprised what a nice CQ DX call can bring up, now that the solar cycle is moving UP!!! As always, your comments about th show are most welcome via INTERNET, to arnie@radiohc.org, and I'll see you on 20 meters CW or via RS13 satellite during the next few days!!!
Arnie Coro CO2KK
Havana, Cuba
17 August, 1999Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba
PO Box 6240, Havana, CUBA 10600
phone: 53-7-814243
phone res: 53-7-301794
e-mail: arnie@radiohc.org
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