Radio Habana Cuba: Dxers Unlimited Mid-Week edition for 12 September, 2000
By Arnie Coro, radio amateur CO2KK
Hi amigos! Hello my friends! This is the mid-week edition of Dxers Unlimited, coming to you during a very special day... The SUN has reached its minimum number of sunspots since the beginning of this year. The daily sunspot number reached a bottom low figure of 27 during the eleventh of September, and only one small, very small solar active region could be observed even with the best optical telescopes! Big contrast with the tremendous activity registered on July the fourteenth, when the daily sunspot count reached the 400 mark!!! More about what's happening 93 million miles from Earth later in today's edition of your favorite radio hobby program.
Now, item two: Recycle, recycle, recycle... yet another source of high quality electronic components for your radio hobby related experiments, and usually in very good shape: dead VCRs, especially the older ones, the real old VCRs have lots of valuable parts that can be recycled very succesfully. The later models, the ones with a high degree of integration, using Large Scale Integration or Very Large Scale Integration, that is LSI and VLSI circuits, will not yield as many parts, but they are still worth taking them apart and recycling everything possible. So if you happen to have an old VCR machine gathering dust in the attic or the basement, or maybe in the garage, this might well be your next relaxing weekend project!!! Take it apart, carefully check and classify all the parts, place them in small bins, and they will be ready there, waiting for your next project. Among the nice goodies that I got from an old BETA standard VCR, are all the components for a nice 12 volts DC power supply that will soon be powering a 2 meter handie talkie!
Item three: Feeding the magnetic loop the easy way, thats the topic coming up after a short musical interval and our station id. Margarita Delgado is the sound engineer and producer, I am Arnie Coro in Havana, back with you in few seconds!
You are listening to the mid-week edition of Dxers Unlimited, coming to you via short wave from Radio Havana Cuba... and here is item three in detail: Magnetic loop antennas can be made rather small, so compact in fact, that they can be placed indoors or in your balcony. Magnetic loops are usually fed using a small loop, about five times smaller than the larger tuned loop, and this system works quite well... but there is another easier way of feeding a magnetic loop, and that is none other than a version of the classical gamma match. You feed the loop with low impedance coaxial cable, say 50 or 75 ohms, then connect the braid or shield of the cable directly to the loop's center, opposite to the location of the loop's tuning capacitor. The coaxial cable's center conductor is then connected at a certain distance from the location of the shield connection. It does take a little experimenting, but once you find the right spot, the center conductor of the coaxial cable can be soldered to the loop itself. By the way -- and answering a question sent in by several Dxers Unlimited's listeners -- your best option for building a self-supporting magnetic loop antenna of about 1 meter or approximately 3.3 feet in diameter is to use copper tubing of between 12 and 25 millimeters, that is from about a half inch to one inch diameter. The copper provides excellent conductivity and if you plan to use your magnetic loop for transmitting, the larger diameter tubing has lower losses.
For a receive-only magnetic loop, you can use a very inexpensive approach: just connect, shorted together, the braid and center conductor of RG213 or similar half inch coaxial cable. Then install the loop using a cross made of wood; it's easy -- you will only need to support the cable at four points, then the loop will have a square shape or a diamond shape depending on how you do it! And again, for receiving purposes, this will make an excellent magnetic loop antenna. Do keep in mind that magnetic loops have to be retuned continuously when you change frequencies, even by only a few kiloHertz. but in my opinion, that is a small price to pay for all the advantages of the magnetic loops as indoor or limited space antennas.
BY THE WAY.. I have a good INFO PACKAGE about how to build magnetic loops, and a few nice photos of very well built magnetic loops, plus links to websites that have a lot of information about this very interesting, and, as you will see, easy to build antenna. INTERESTED? Well, just drop me an e-mail to arnie@radiohc.org.
I am sure that after seeing how nice they look and how easy to build they are, you will jump onto the bandwagon and make yourself a magnetic loop antenna as soon as possible!
From antennas now we jump to item four: homebrewing radios, and nswering questions sent in by listeners like you, who are just starting to learn more about this fascinating hobby.
Question, from Vermont, USA: Arnie, I saw an old 1937 Radio Handbook in the library, it shows breadboard construction techniques. Can we still use them?
YES OF COURSE, and breadboard-built replicas of vintage radio gear are one of the most enjoyable ways of having a nice time playing with radios. One good example of this construction technique is running two boards with a slit in the middle that fits exactly the diameter of the old 8-pin octal or similar vacuum tube sockets. All it takes is to assemble four pieces of wood with nails, and your chassis is ready to receive the sockets. I have built several regenerative receivers and low power transmitters and a power supply using this low-cost approach. One-inch or three-quarter-inch plywood seems to be ideal for the job. So, amigo from Vermont, start gathering parts and try building first a power supply for vacuum tube equipment, always keeping in mind that you have to be extremely careful handling it, as the high voltages involved -- typically between 150 and 250 volts DC for receivers and low power transmitters -- have to be dealt with very carefully indeed! But go ahead anyway, and build your power supply and then test your abilities building a simple two-stage audio amplifier, which you can then use as yet another electronic workshop test instrument. Next step is to try a simple regenerative receiver, for which I have several easy to build circuits available here too... just send your request for the simple vacuum tube vintage radios circuits to arnie@radiohc.org or via Air Mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
Your radio is tuned to Radio Havana Cuba, the name of the show is Dxers Unlimited, and yes amigos, despite the very low solar activity, due to equinoctial propagation conditions, the three higher amateur HF bands -- 15, 12 and 10 meters -- are providing hams around the world with very nice two-way contacts. Here in Havana, 10 meters has opened every late afternoon to Japan, and just one short CQ call from CO2KK seems to raise quite a pileup in a few seconds when the Japanese stations realize that the band is open to the Caribbean. By the way, Japan happens to be, according to the International Amateur Radio Union, the nation with the highest number of licensed radio amateurs!!!
Now item five: Answering yet another question that came also from the USA; a listener in Minnesota asks: Arnie can I use the coaxial cable marked RG58U that the computer network people here are discarding because they have changed to UTP type twisted pair?
Sure amigo, grab as much of that computer network coaxial cable as you can; it is usually a very high-quality version of the lower cost RG58U, and has a very tightly woven shield and sometimes even an extra foil for better shielding. You will only need to buy a crimping tool and the best possible quality crimp on BNC and PL259 connectors. If there is lots of cable available, take it home, organize it, and make it available to other radio enthusiasts, perhaps at your radio club, or to the new kid starting to learn about radio. SI SI SI, YES YES YES, computer networking 50 ohm cable is very good for radio hobby use, and due to the fact that it was used indoors, it is usually in a like-new condition, even if it has been in service for several years. Remember to buy a good-quality coaxial-cable crimping tool and connectors! And, yes, you will need some practice to install those crimp-on connectors the right way, so try to learn from the technicians that use them regularly, and practice until you do it properly!
And now amigos, at the end of the show, as always, free of charge, freeware, in the public domain, here is Arnie Coro's HF plus 6 meters propagation update and forecast: Solar activity may hit the very low mark during the next two to three days, solar flux going down to 120 units or even lower. The daily sunspot number was a record low of just 27 this past Monday, and the next few days may show a spotless disk too. BUT beware -- this does not mean that the solar maximum is over, according to solar scientists; most of them agree that this is part of the ups and downs of the solar cycle.
Now some practical propagation remarks: Best Dx conditions during the equinoctial period will occur during the late local afternoon hours and about one hour or two after sunset; then we will see another peak in propagation between about 10 pm and 1 am in the morning local time, and a third peak will show up starting around 5 am in the morning until about an hour after sunrise. Due to the very low solar flux, the daily maximum useable frequency figures will be rather lower than we could have expected with solar flux figures of 150 or higher; nevertheless, if we do not have to deal with coronal hole activity further on in the week, ionospheric absorption should be low, and propagation will be normal for the season.
Don't forget to tell me your opinion about this show, give me new ideas on what might be interesting and also send me a signal report for your QSL!!! Send via e-mail to arnie@radiohc.org and via Air Mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
prepared 12-Sep-2000; transmitted 13-Sep-2000 16:09
Arnie Coro CO2KK
Havana, Cuba
12-September, 2000Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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