Radio Havana - Dxers Unlimited mid week edition for 29-30 May 2007
Hi amigos radioaficionados around the world, and in orbiting in space …
I am Arnie Coro radio amateur CO2KK welcoming you to my twice weekly radio hobby program that attempts to cover the more than 81 ways you and I enjoy our hobby, from participating in an exhausting whole weekend amateur radio contest to relaxing at a beach resort listening to a far away AM broadcast band station that is heard on your little portable radio with a nice and clear signal thanks to that interesting
propagation effect known among experts as sea gain… Sure, this hobby is always challenging, and when you think that already you have gone through all the possible aspects of it, then someone comes out with a radically new antenna, a new communications mode using computers or suddenly finds out that there is still a lot of room for experimenting at the millimeter wavelengths… Si amigos, yes my friends, oui mes amis in Canada and the French speaking Caribbean that listen to this program,
radio is simply fascinating… Take for example this past weekend CQ Radio Amateur magazine WPX CW contest, when thousands of amateur radio stations around the world went on the air to try to work as many new prefixes as possible…
According to my own observations and comments overheard on 40 meters after the constest was over, the WPX contest this weekend was favoured by fine conditions during its first part,that is from Satuday at 00 UTC when it started , that was
Friday evening for us here in the Americas, but then Sunday UTC was not so good with little real DX stations heard. Among the rare goodies picked up on the ham bands, the really hard to rk prefixes I heard the rare 3V8BB from Tunisia operating on the 40 meters band, on 7033 kHz.
He had already gone past the 2100 contest points, which is outstanding. Other maybe not so rare, but nevertheless interesting stations heard during the weekend WPX ham radio CW contest included 9K2HN Kuwait on 15 meters using 21030 kHz when the band opened for a few minutes from Cuba that that part of the world, I also heard someone
working HL2AEJ Korea on14009 kHz, but no luck trying to pick up the Korean station. The not too frequently heard 4L prefix, from Georgia came via 4L8A, an excellent CW.
And new prefixes continue to be assigned to amateur stations in countries with a deep rooted tradition in promoting our hobby; that is the case of the prefix 5P7 , that I had never heard before… it took some time to find out that it was a station from Denmark using the callsign 5P7Y during the contest. Othe stations heard- included C4I Cyprus on 2 meters , using 14028 kHz, and an operator from Central Siberia, usin the callsign RK0UT that went past the normal CW self imposed boundary of around 14065, and insisted on calling CQ around 14075 kiloHertz, and to my surprise, he did made several contacts during the time that I listened to him. By the way, I didn’t operate during the contest, as I had a very busy weekend schedule, but did enjoy some amateur bands short wave listening , that gave what you have just heard as a practical result.
And before going over to the next item, once again the world heritage site of the Ecuadorean GALAPAGOS ISLANDS was on the air during an amateur radio contest, HC8N heard on 7005 kHz CW. The operators was announcing at QRZ.com that he will be QSLing QSL via W5VE . More radio hobby related information follows as Dxers Unlimited’s mid
week edition continues…
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This is Radio Havana Cuba , the name of the show is Dxers Unlimited, and here is our next item in today’s mid week edition of the program… More about compact antennas for HF and some interesting antenna modeling done in real life, in actual practice, not using computers… Scale model of HF antennas done at VHF frequencies provide a lot of practical information and are easy to reproduce and modify. For example , a working model for the two meters amateur band of the electromagnetic ground plane antenna system, proved that using a proper ground system, the efficiency of the
EMGP vertical antenna will match the radiation efficiency achieved by a full size quarter wave vertical to within a very small percentage… As a matter of fact, very carefully done field intensity comparative measurements between a full size quarter wave 2 meters band vertical placed at the center of a metal plate that has a diameter of one meter, and an EMGP antenna cut for the same 145 megaHertz center frequency proved to be almost exactly the same… A very interesting finding if you
take into consideration that the EMGP antenna’s height above the ground plane is just 1/12 of a wavelength , that for the 145 megaHertz center frequency is just 17 centimeters or just six points seven inches… Now compare this antenna height with the 19 inches or around 49 centimeters required by the full size quarter wave or 90 electrical degrees hig antenna system.
For two meters band operation , the extremely low profile antenna will be an excellent choice for an antenna to be used when extremely strong winds are expected, like when a hurricane is approaching. An EMGP or electromagnetic ground plane antenna for the 40 meters amateur band, will be only about three and a half meters high above the ground plane, but I must clarify to my listeners that it would not be a very good emergency antenna because it will not have enough high vertical angle
radiation , something that is essential for short range Near Vertical Incidence Skywave propagation, as required for short range communications within an affected area.
Nevertheless, modeling the EMGP as a “real life” antenna on 2 meters proved to be a very interesting and rewarding experience, and something that was done in just a few hours of my weekend spare time… If you don’t have enough space where to install a short wave antenna system, don’t overlook the possibility of homebrewing an EMGP antenna, that when properly made, will provide reasonable results on the band for
which it is cut on transmit, and good receiving on the next lower and higher adjacent bands. If you want to know more about the EMGP , the Electro Magnetic Ground
Plane antenna, send me an e-mail to arnie@rhc.cu, and I will reply with the EMGP Antenna Design Package, with detailed instructions on how to homebrew these antennas for the amateur bands between 80 meters and 2 meters…
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Si amigos, yes… ASK ARNIE continues to be at the top of your preferences, according to the e-mail messages, letters and actual on the air two way amateur radio contacts… Here is ASK ARNIE today answering question sent by listeners Gail in Georgia USA, Armand in California also USA, Virgil , who listens to 6000 kiloHertz very late at night from his Southern England QTH, and Barry, who picks up our 9550 kiloHertz signals in New Zealand with amazing good quality as he tells me in his
e-mail. They all want to know more about the Spiral end loaded antennas recently mentioned here at Dxers Unlimited, and in the case of Barry, who happens to be a very enthusiastic radio amateur operator, he wants to know the difference between the Petlowany and the Tak antennas, if there is any difference at all… Well amigos, the spiral end loaded antennas are really nothing new at all… I remember reading about spiral loaded antennas for the very low frequencies a long time ago, in an article that presented an extensive review of several types of top loaded antennas for operation on very low and extremely low frequencies. Then some time after reading that article, I went to Cardenas , a city of Matanzas province that has a
very nice seaport , where a coastal radio station operating on the now no longer used 600 meters or 500 kiloHertz marine band was installed. To my surprise the vertical antenna located an an excellent salt marsh swampy area on one side of the bay, had a rather large sized top hat to provide additional loading to the about 70 meters high tower, that was physically too short to resonate efficiently on the 460 to 512 kiloHertz band where it had to operate. This was just a capacity hat made of
spokes and wires, and not a spiral top loading of the tower. Several months later I had the nice opportunity of talking to the designer of that low frequency band antenna system, and he told me that due to the complexity of the spiral loading configuration, he had opted for the much simpler capacity hat, but he added that a spiral loading system proved to be much more efficient when he was doing “the numbers”, that meaning when he was calculating the new antenna for the marine
communications site. I asked him about the size of the projected spiral loading device and he said that even when made with the same diameter as the capacity hat, the spiral was much more efficient and provide much better loading of the structure, something that is essential on those very short antennas for the long waves… Then, he told me about an experiment that ran under his supervision, when two engineering students that were writing their thesis , made a 10 megaHertz scale model of the
500 kiloHertz antenna system… in other words a one twentieth scale ratio. The students, the designer said, had much more time to play with the antenna’s top loading, and they found out that winding a one quarter wave of wire into a spiral of enough diameter , the antenna’s resonant frequency went down dramatically while retaining a rather high radiation efficiency. But again, he added, the main problem was not of an electrical nature, but one related to the mechanical complexity of
keeping the spiral wound loading device in place at the top of a tower when heavy winds were blowing.
In the case of both the Petlowany and the Tak spiral loaded antennas, because they are both dipoles used in a horizontal configuration, keeping the end loading spirals in good shape is not as complicated as with the high towers…
So, amigos, now you know a bit more about spiral loading of antennas, and why the Petlowany and the Tak antennas are almost identical !!!
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Now ready to copy, as the program is coming to an end, and Arnie Coro’s Dxers Unlimited’s HF plus low band VHF propagation update and forecast will now go on the air… Solar activity was at extremely low levels, with ZERO sunspot count and the solar flux at 70 and even below… So, the daytime maximum useable frequency continues to be only reching barely above 20 megaHertz for short periods, and staying even below 15 megaHertz on some circuits … The chances for Sporadic E propagation
events are now coming to their maximum for the year, as we enter the month of June…There is great expectation for the upcoming ARRL June VHF QSO Party Contest, because if the very low solar activity continues , we may see some really big sporadic E events happening, that the operators of Cuba’s main entry in the contest, special prefix callsign T49C , hope to make very good use to once again win that contest.
Hope to have you all listening to the weekend edition of the program that will be on the air Saturday and Sunday UTC days amigos, and don’t forge to send your signal reports, QSL card requests and radio hobby related questions directly to arnie@rhc.cu, again, arnie@rhc.cu or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba
