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Re: [HCDX] Dxers Unlimited short form mid week edition for July 17-18 (Shorter because of the extended Pan American Games coverage by RHC)
Radio Habana Cuba
Dxers Unlimited
Dxers Unlimited's mid week for 17 - 18 July 2007
By Arnie Coro
radio amateur CO2KK
Hi amigos radioaficionados worldwide..., and those of you in space orbit
too... with our now traditional salute, a special short form edition
Dxers Unlimited's mid week edition begins , the reason for today's
shorter program is that ready to bring you lots of practical radio
hobby information... I am Arnie Coro, radio amateur CO2KK, your host
here in Havana and here is item one: Many listeners have written asking
about the possibility of using a single antenna for covering a wide
range of VHF frequencies, so today in our ASK ARNIE section of the show,
I will be telling you about two popular antennas that offer broadband
coverage ... one is omnidirectional and the other has a directional pattern.
Item two: Another antenna related topic...by using a pararell open wire
feedline connected to a dipole, you can actually operate the system as
three antennas with very different characteristics... Mode ONE: as a
standard dipole, MODE 2: as a T antenna working against a good ground
system and MODE 3: As an inverted L by using one leg of the open wire
feeder against ground... By arranging for the proper switching, the
THREE IN ONE antenna system provides you with a lot of possibilities. At
CO2KK, my ham radio station, I have a three wire on each leg fan dipole
fed with 400 ohm open wire line... The fan dipole by itself is an
excellent antenna for the frequency range between 7 and 21 megaHertz,
using a wide range PI network antenna tuner... By connecting together
the two wires of the transmission line, the antenna works very nicely on
the 80 meters amateur band in what is known as a T antenna
configuration, but it does need a counterpoise, or ground system in
order to work properly as a T antenna. I also use it with just one of
the wires of the open line , so that the antenna works as an inverted
L..., again working with a ground system. So, now you know why I have
named this system the THREE IN ONE ANTENNA...
By making the legs of the dipole at least 10 meters long , an excellent
frequency coverage is achieved...For the lower frequencies, longer legs
improve the performance of this antenna a lot.
More radio hobby related information coming up as Dxers Unlimited's mid
week edition continues in a few seconds
......
Si amigos, you are listening to the mid week edition of Dxers Unlimited,
and as announced at the start of the program , here is LA NUMERO UNO,
the most popular section of the show, ASK ARNIE. answering a request
about broadband antennas for VHF monitoring... By the way,monitoring VHF
communications as well as the VHF amateur bands is one of the more than
81 ways of enjoying the radio hobby... But , monitoring the VHF range
from about 40 megaHertz all the way up to about 170 megaHertz requires
using a broadband antenna... For general purpose monitoring 360 degrees
around the compass, there is one antenna design that works very well,
and is not too difficult to homebrew... it is known as the DISCONNE
ANTENNA, and I happen to have at hand here, ready to be sent to any
Dxers Unlimited listener wanting to build a DISCONNE, an excellent
design program... The freeware program lets you calculate a DISCONNE is
less than two minutes... And I can assure you that antennas built
following the dimensions obtained from the disconne design software work
very well indeed... My two favorite designs for discones are one that
has a low frequency cuttoff of around 40 megaHertz , with theoretical,
but not in actual practice high frequency limit of 400 megaHertz, and
another design that starts operating around 100 megaHertz and that will
again, in theory will reach as high as 900 megaHertz or even higher...
From the above information you can see that the frequency range of a
typical disconne is almost a ten to one frequency ratio...but there is a
problem with these antennas as the frequency goes up.You will still have
a nice match, typically less than 2 to 1 standing wave ratio, but the
take off angle will move upward as the frequency changes to a higher
value, this shift in the vertical take-off angle of the discone is an
outstanding characteristic of this unique antenna system, that is fed
directly using 50 ohms coaxial cable, and requires absolutely no
matching system...
QSL , yes QSL on the air amigos... QSL on the air to the many Dxers
Unlimited's listeners that have sent e-mail messages to arnie@xxxxxx,
requesting a QSL card from Radio Havana Cuba, sending very accurate
reception reports and providing me with many good ideas on how to
improve the program...now , here is our next item of today's show...
This is the technical tips section of Dxers Unlimited... today I will
tell you about how to reduce power line interference by installing a
power line filter between the wallplug where you connect your radio
equipment and the radios... A three section homebrew filter, with a
proper ground connection prevents power line noise from entering your
radios and causing harmful interference... There are several well built,
but expensive , power line filters, so your best option is to homebrew
one, just as I have done here at my listening post and ham radio
station. The filter is capable of passing an AC power line current of 6
amperes, more than enough to power up all my equipment, except the high
power linear amplifier...The power line filter is very effective in
removing noise coming from nearby switched mode power supplies , like
the ones used by computers.
I am now working on a step by step instruction manual with full
graphics, so that you can homebrew this type of filter, that does
require a lot of metal work, as it most be totally shielded in order to
be really effective. As soon as the manual is completed, I will be
announcing it here at Dxers Unlimited...
......
arnie@xxxxxx, that's my direct e-mail address, arnie@xxxxxx, always
ready to receive your comments about the program, signal reports, QSL
requests , and any radio hobby related questions that you may want to
send to our popular ASK ARNIE section of Dxers Unlimited...
And now amigos, as always at the end of the show, our exclusive and not
copyrighted HF plus low band VHF propagation update and forecast...Solar
flux is hovering now very near the baseline activity... latest reports
show that the flux was around 72 units, just five units above the 70
figure that scientists consider to be the minimum baseline activity ...
The effective sunspot number was at ___30____ at around noon local
time here in Havana, and the A index was a nice and low 02... Expect
propagation to improve somewhat by Thursday, when the effects of the
solar wind will vannish... Hope to have you listening to my show's
weekend edition next Saturday and Sunday UTC days... and don't forget to
send me your signal reports and comments to arnie@xxxxxx, or VIA AIR
MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
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