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Re: [HCDX] Dxers Unlimited's week end edition for 3-4 November 2007
Radio Habana Cuba
Dxers Unlimited
Dxers Unlimited's weekend edition for 3-4 November 2007
By Arnie Coro
Radio amateur CO2KK
Hi amigos radioaficionados worldwide... with our traditional salute,
Dxers Unlimited’s weekend edition begins, 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 a popular antenna that
offers broadband coverage. It is omni directional, that meaning it
receives signals from all around the compass and also it is not too
difficult to homebrew.
Item two: Another antenna related topic...by using a parallel open wire
feed line connected to a dipole or how it is known among experts a FAN
DIPOLE,, you can actually operate the system as three antennas with very
different characteristics... Mode ONE: as a standard half wave 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 of
course that it does need a ground return made, at my location by
several ground radials
or what was known in the early days of radio as a “counterpoise”.
I use one of the wires of the open line, in another configuration, so
that the antenna works as an inverted L... 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, excellent
frequency coverage is achieved...
More radio hobby related information coming up as Dxers Unlimited's
weekend edition continues in a few seconds
.....
Si amigos, you are listening to the weekend 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 DISCONE
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 DISCONE is
less than two minutes... And I can assure you that antennas built
following the dimensions obtained from the discone design software work
very well indeed... My two favorite designs for disconnes are one that
has a low frequency cutoff of around 40 megaHertz , with a high
frequency limit of 400 megaHertz, and another design that starts
operating around 100 megaHertz and that will reach as high as 900
megaHertz or even higher... From the above information you can see that
the frequency range of a typical discone is almost a ten to one
frequency ratio... an outstanding characteristic of this unique antenna
system, which is fed directly using 50 ohms coaxial cable, and requires
absolutely no matching system...
Again, you can homebrew disconnes for any frequency range, with the
design parameters that you feed to the computer software program... A
friend of mine , who spends most of his spare time monitoring the
aviation band in the range from 118 to 136 megaHertz , has built a
discone with a low frequency cutoff of 110 megaHertz, that he has tested
all the way up to the 800 megaHertz frequency range very successfully.
His antenna was built during a weekend, using copper wire and a small
piece of Plexiglas insulation to separate the cone from the disk... He
used an aluminum disk for the top of the antenna, and copper wire spokes
to form the cone...
More about broadband antennas for VHF monitoring after a short break...
.....
You are listening to the weekend edition of Dxers Unlimited, coming to
you from Radio Havana Cuba, and for those listeners that have requested
the data file about the QUATRRO CRYSTAL RADIO RECEIVER, let me tell you
I made a new drawing of the schematic diagram, as the original file was
yet another computer crash casualty... So, be patient amigos, I will
e-mail the four diode crystal radio diagram by the end of the week...
Now, the program continues with information about the second type of
broadband antenna for VHF monitoring. In this case, it is a directional
system, known among experts as a log periodic array of dipoles...This
antenna is rather complex from a mechanical point of view, but it can be
built using the proper tools and following a good design. My favorite
log periodic for VHF monitoring covers from 45 megaHertz to 150
megaHertz, and it does require the use of an antenna rotor. A second
smaller log periodic for the frequency range 100 to 500 megaHertz has
provided excellent service for monitoring, as well as for operating the
two meters, one and quarter meters and 70 centimeters amateur bands...
Again, home brewing a log periodic antenna is not a very easy job, but
believe me amigos, that time spent building your own log periodic for
VHF-UHF monitoring is well worth every single minute you devote to its
construction...and you will certainly save a lot of money, as
commercially built log periodic antennas are very expensive.
The typical log periodic antenna is also designed for 50 ohms coaxial
cable feed, and again, it is a highly directional system that requires
the use of a rotor to pinpoint the antenna in the direction you want to
pick up signals or to transmit.
There are several very well written software programs for designing VHF
and UHF log periodic antennas, and I have here two of them, ready to be
e-mailed to any of you Dxers Unlimited's listeners around the world that
may want to explore the possibilities of home brewing your own broadband
log periodic antenna...
.......
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 wall plug 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 TV sets VCR and DVD machines.
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...
You are listening to the weekend edition of Dxers Unlimited, that goes
on the air Tuesdays and Wednesdays UTC days.... and here is our next
item of today's program... Satellite direct broadcast radio is very
slowly growing in listenership, but this is happening only in developed
countries... the number of satellite radio receivers capable of picking
up direct broadcasts from Earth orbit in third world nations is
extremely small, something that can be easily explained for two obvious
reasons... one, the receivers are much more expensive than common radios
AM broadcast band short wave and FM radios... and two, most of satellite
radio services require paying for a monthly fee that in many cases may
be easily the equivalent of what a person in some places of Africa ,
Latin America or Asia, receives as income for many months of hard
work... So, short wave radio is here to stay amigos ... and yes, we may
see more satellite radio receivers sold in Third World nations, but only
to people of above average income...who can pay for the radios, and also
for the monthly fees asked by the operators of the existing satellite
radio systems...
...
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 continues in its now almost endless hovering very near the baseline
activity... latest reports show that the flux was around 67 units, just
three units above the 64 figure that scientists consider to be the
minimum baseline activity ever registered ... The effective sunspot
number was very low at around noon local time here in Havana, an SSN of
6 . Expect HFpropagation to continue to be very poor .The optical
sunspot count was ZERO, again ZERO, and expected stay at zero or very
slightly above for the rest of the week. Hope to have you listening to
my show's midweek edition next Tuesday and Wednesday 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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THE INFORMATION IN THIS ARTICLE IS FREE. It may be copied, distributed
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