RADIO HABANA CUBA HI AMIGOS WORLDWIDE! Welcome to the weekend edition of your favorite radio hobby show on shortwave... of course!
DXERS UNLIMITED
WEEKEND EDITION
SATURDAY, 28 FEBRUARY, 1998
By Arnie Coro
SEND YOUR COMMENTS, QUESTIONS AND IDEAS DIRECTLY TO ME AT: arnie@radiohc.org
I am Arnie Coro, radio amateur CO2KK, your friend here in Havana, and it's my pleasure to be able to share with you about 16 minutes of all radio hobby related information... As always, first things first... so here is an update on HF propagation......
Solar flux a little down from last tuesday-wednesday edition of Dxers Unlimited, but the effective sunspot number is holding pretty well above the 40, four zero mark, and that amigos keeps things going, as there is a definite accumulative effect, or charging of the ionosphere that keeps the free electron concentration above a certain level, NOW if this sounds a little too complicated... don't worry, all you need to know is that solar cycle 23, although not all that great yet, is doing well.
From my latitude 23 degrees north position, I am enjoying daily openings on the 10 meter amateur band to the south, now for many hours every day...lots of argentinian and brazilian amateurs heard here in Havana with very simple antennas...
More about shortwave propagation at the end of the show... Now here is item two for today...
The Eclipse... Click here to see it!
In Cuba, the best location to watch it was way to my southeast... Guantanamo province in eastern Cuba could catch a 72 percent partial eclipse, here in Havana it was less than that... but anyway, scientists at the Instituto de Geofisica y Astronomia, the Geophysics and Astronomy research institute had a field day with the eclipse, recording every single second of it using all available instruments, including several special solar radiotelescopes, working at different wavelengths...My own personal observations consisted in watching the 21 megahertz, or 15 meter amateur band, and the adjacen 13 meter international broadcast band... to try to look for a well known effect, known as the F2 layer notch, which happens during a solar eclipse... with my primitive setup, I could see a no less than 6 dB attenuation on a signal coming from the south of me, which unfortunately was using the SSB mode, so it was a real difficult task to measure and average the peaks... Anyway, it was enjoyable, and it proved to be both an optical and radio event followed by millions around the world thanks to TV and Internet coverage...
More radio hobby related information follows in a few seconds.
My sound engineer and producer... Margarita Delgado... the name of the show is Dxers Unlimited, you are tuned to Radio Havana Cuba, and as promised here is some additional information on the QUAD antenna... As I already told you during the midweek edition of the show, the QUAD's driven element is just a one wavelength loop to which you attach the feedline... This loop may have many different shapes, but there are too which provide the highest efficiency according to my tests... A CIRCULAR ONE WAVELENGTH LOOP is the optimum shape, followed by a perfect four sided square... You can use the DELTA or triangular loop configuration, it works OK, and sometimes it's about the only choice when installing a ONE WAVELENGTH LOOP, but again, the CIRCULAR AND SQUARE loops are best.
Remember I was going to give you an approximate formula for calculating the QUAD driven element... it is good enough at HF, from around 5 to 50 megahertz... But follow Arnie Coro's advice, and DO CHECK YOUR LOOP's RESONANT FREQUENCY with a grid dip meter, an instrument which is about the most valuable pieces of test gear a radio enthusiast can own... SO HERE IS THE FORMULA.... if you want to calculate the overall length of the QUAD or of the CIRCULAR LOOP, using standard wire for building it, the formula is the number 1005 divided by the frequency in megahertz, and the answer will come out in feet.
Now, may I repeat the formula just in case. This is the formula for calculating the length of wire needed to make a one wavelength element... which you can configure into different shapes... from the ideal circular loop to the less than ideal delta or triangular loop. OK, here it goes again, the number is 1005 -- one, zero, zero, five -- divided by the frequency in megahertz... and the answer will come out in feet, which you can convert very easily to metric by dividing the result by 3.28.
OK, what about a test run.... let's calculate a one wavelength loop for the fifteen-meter amateur band, an antenna that will also provide nice performance on the 13-meter international shortwave broadcast band... SO... 1005, divided by 21.225, which is the center of the 21 megahertz ham band, gives us an overall length of... let's see 47. 34, almost 47.35 feet... now if we want the answer in meters, easy too... divide by 3.28 and here comes the answer, 14.43 meters...
Now, if we want the antenna to have a square shape, one that is an easy approach from a mechanical point of view, we only need to divide our results by 4, to find out the length of each side of the square... Here we go... if we use the metric result, 14.43 meters, each side of the loop would be 3.60 meters or.... 11 dot eight three feet... In other words, your antenna will be a four sided square with each side running 3.60 meters of 11 dot eight three feet...
HOW DO YOU SUPPORT THAT WIRE? That's a good question, there are many different ways of MECHANICALLY designing a LOOP, You can use fiberglass spreaders to keep the wire in the proper shape, or you can hold the sides of the loop with insulating rope into position, using masts or tree as supports. You can make your loop rotatable, which is ideal, or just install it in a fixed position. REMEMBER THAT A SINGLE LOOP ELEMENT will provide about 2 dB gain in TWO DIRECTIONS; if you want to make this antenna unidirectional, you must add at least one more element.... which may take the form of a REFLECTOR or a DIRECTOR, depending on the position in behind for the reflector, or in front for the director... You can also make very nice high gain loop antennas by combining several circular, quad or triangular elements into a parasitic array, something very similar to a Yagi... technically speaking it is known as a slow wave structure... But never mind about the fancy name...
As airtime is tight, I will provide additional information about the one wavelength loop antenna at our website, with dimensions for some of my favorites there. Surf the net, and make a bookmark at: www.radiohc.org
Again, go to our website, www.radiohc.org and click Dxers Unlimited for more radio hobby related information, including the scripts for the show. Yes, the full text of this show is available at our WEBSITE. You can downloaded and read the text whenever you have time. Another very special service of Radio Havana, Cuba to its worldwide audience!
Lots of e-mail for QSL on the air... but I'll leave it for the mid-week edition, so that more technical information will be packed here today.
Surprised with results with the simple Tuned Radio Frequency receiver that he built, a local amateur decided to run some tests receiving shortwave stations.. with a three transistor TRF, one for the RF amplifier and two for audio, he is able to listen to more than 50, yes, five zero international broadcast stations on the 6, 9, 11 and 13 megahertz band...
The secret? Something I have told Dxers Unlimited's listeners many, many times... my friend spent more time designing and building the TRF receiver's input circuit than what he spent building the radio itself.. A triple-tuned input circuit with a signal attenuator makes the whole difference... he brought it to my home QTH for testing, and I was really amazed by the results... Then, as he always builds MODULAR.
I tried the triple-tuned input circuit and attenuator on my little SONY ICF7600D, which is now about to die due to keypad contact problems... WHAT A DIFFERENCE... tuning on the very crowded 31 meter band was much nicer with the triple tuned circuit, which my friend made using an old three section 9 to 365 pF variable capacitor, three hand-wound air coils which he shielded very well from each other, and the beautifully built signal attenuator providing steps of 3 dB from 0 to 60 dB... A work of art... a beautifully built, completely shielded box... which, by the way, could be a very good addition to any small portable receiver... The circuit is just the three-section variable capacitor, three hand-wound coils using PVC plumbers pipe for a coil form, and two small trimmer capacitors that top connect the three tuned circuits together. The output is via a tapped link, providing optimum match for different frequencies... I think this really deserves a posting at our WEBSITE... let's see if I can find enough time to write it up next week!
First time listening to shortwave, or maybe you have already spent a few days, maybe a week or two, enjoying shortwave listening... Yes, it's different from the local FM BOOMBOX... SURE!!! And quite a change from the AM talkshow host ... right!!!
Also shortwave listening provides you with a different perspective, and the possibility of learning all by yourself more about this world of ours. Also this is a hobby, you can ask the stations to confirm or verify reception... and start a collection of station verifications or QSL's... here is how to do it... send a signal report and comments about this show directly to me... via the INTERNET... very easy, mail to: arnie@radiohc.org
Slowly again... mail to: arnie@radiohc.org... and if you are not yet into cyberspace, don't worry, you can send your QSL request via air mail to:
Arnie Coro
Dxers Unlimited
Radio Havana Cuba
Havana, CubaAs easy as that... again, Arnie Coro ... that's me! Radio Havana Cuba, Havana, Cuba
Now more radio hobby topics...
A question-and-answer session... question sent in by a listener in Australia, who happens to enjoy nice reception of our 9820 kHz Pacific Coast of North America Beam! Signal just keeps travelling across the Pacific and make it to Australia quite well when the sunspots are good enough... His question follows...
Dear Arnie... need to buy a new radio... my 20 year old box is just falling apart... Any ideas on what should I buy?
That's a tough question.. first I must know your budget... but anyway, here is my advice... try to buy yourself a receiver that is digitally tuned, very important, be medium sized... as very small radios are not typically good performers, although there are exceptions... and above all TEST THE RECEIVER AT YOUR LOCATION if possible before buying...
Look for a radio that has a BFO, that means that it can receive single side band and CW signals.... There are several receivers that meet this set of specifications including some that have been around for quite sometime, but for one good reason are still manufactured! If you want a more expensive table top model, there are now several from which to choose, but do prepare your pocketbook, as they can be really expensive sets!!! Finnally a word of caution... USED RECEIVERS, should be approached very, very carefully... unless you are already an electronics wizard and prepared to repair the unexpected! Hope this answers the question... if you need more advice on a specific set, just e-mail or write via air mail to me, and I'll gladly try to help!
Now, just before going QRT, here is Arnie Coro's HF propagation update and forecast valid for the next five days:
Expect solar flux to continue between 85 and 95.. we may see a sudden outburst of solar activity if a new active region developes, if not, the sun's output is going to be going down for the next three to five days. The Earth's geomagnetic field, so important for the F2 long range propagation is expected to remain from quiet to unsettled. As we continue approaching the spring equinox, the bands will keep open until later in the evening... You will notice a definite improvement in reception of the 19 meter broadcast and the 20 meter amateur band after your local sunset! Daytime Dx will continue to be at its best in the segment from 18 to 30 megahertz, but especially from 18 to 25 megahertz... AM band Dxing will not be very good, and the same holds for tropical band Dxing, but this two will improve during the peak of the equinoctial season...
See you at the weekend edition of the show, and remember our website is: www.radiohc.org with fast, easy downloading!!!
Arnie Coro CO2KK
Havana, Cuba
28 February, 1998Postal 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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