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Re: [HCDX] Dxers Unlimited's script mid week edition May 29-30 2007
Radio Havana Cuba
Dxers Unlimited
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
work 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 20
meters , using 14028 kHz, and an operator from Central Siberia, using
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…
………
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 high
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@xxxxxx, 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…
……
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 a
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 !!!
…..
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@xxxxxx, again, arnie@xxxxxx or VIA
AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba
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