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Re: [HCDX] Dxers Unlimited's mid week edition for 3 -4 July 2007
Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited midweek edition for 3-4 July 2007
By Arnie Coro
Radio amateur CO2KK
Hi amigos radioaficionados!
Welcome to the midweek edition of your favorite radio hobby program,
coming to you from sunny Havana, where summer weather is providing us
with beautiful days for going to the beach!!! I am Arnie Coro, radio
amateur CO2KK, your friend here in Cuba, now ready to read today’s menu:
ITEM ONE TV DX and FM band season well in progress at this moment, with
sporadic E skip events happening all around North America, the Caribbean
Europe and Northern Africa. Several recent sporadic E opening sent the
maximum useable frequency up to the FM band, making reception of FM
broadcast stations from more than one thousand miles away possible, even
with handheld radios and their telescopic whip antennas, as it happened
here this week, when I was able to pick up a Chicago FM station on my
portable radio while sitting in my balcony !… More information about the
sporadic E season later at the end of the program when Arnie Coro’s HF
plus low band VHF propagation update and forecast will be on the air...
ITEM TWO: Oscar 40 the ill fated amateur satellite that failed shortly
after it was placed in orbit is certainly missed by the world’s amateur
radio operators. Remember that this was a unique satellite designed to
orbit the Earth using a very special elliptical orbit that would make it
available for many hours at a time, just short of a geosynchronous
orbit, the so called MOLNYA orbit, that is an excellent choice for any
upcoming ham radio satellite that will hopefully replace the doomed
OSCAR 40, that had big problems from its very few hours in Earth Orbit.
ITEM THREE: Listeners questions continue to come in via e-mail,
postcards, letters and fax messages, and I have quite a backlog of them
here waiting to be answered… a recent one from Chile, really surprised
me, as normally the show is not heard so far South of Havana… But the
use of 11760 kilohertz with our omni directional
6 dB gain array of dipoles antenna explains why English speaking
listeners from Chile are picking up Dxers Unlimited...very late in the
evening their local time, as we use that frequency from 05 to 07 UTC to
broadcast our English language program .
ITEM FOUR: More about low cost , easy to build ham radio antennas, and
at the end of the show, our exclusive and not copyrighted HF plus low
band VHF from 30 to 120 megaHertz propagation update and forecast. Stay
tuned for more radio hobby related information, coming to you from
Havana. I am Arnie Coro ready to be back with you in just a few seconds…
….
Si amigos, yes my friends, you are listening to Radio Havana Cuba, the
name of the show is Dxers Unlimited, and YES, we do QSL here one hundred
percent, we do verify reception reports and we do it absolutely free of
charge, as all short wave radio stations should do… Send your signal
reports and comments about the program to arnie@xxxxxx, or VIA AIR MAIL
to Arnie Coro, Radio Havana Cuba,
Havana, Cuba, And NOW , here is ASK ARNIE, THE most popular section of
Dxers Unlimited, according to your e-mails, postcards and letters amigos …
QUESTION number one for today: From listener Scotty in Maryland, Scotty
wants to know why old radio magazines – he said that he got a bunch of
them recently from a friend and found them very interesting to read, he
added that those magazines often mentioned the use of so called
“converters” ahead of short wave receivers to pick up the higher
frequency bands. Well amigo Scotty, a converter is nothing but a
complete front end of a radio receiver, it usually includes a radio
frequency amplifier stage, a mixer and a local oscillator. The RF stage
for the VHF bands used the best available vacuum tubes that provided
good gain and low noise, and the really good converters used a crystal
controlled local injection oscillator. Even today, adding a homebrew
converter ahead of a low cost receiver can provide outstanding results,
especially with radios that lack front end selectivity. A few days ago
amigo Scotty, I removed a lot of dust from a three vacuum tube six meter
band converter that was in storage in my garage for many years… it
required 6.3 volts filament voltage and 150 volts DC to operate.
Powering it up from one of my workbench power supplies, I connected the
more than 40 years old converter to a modern digital portable receiver,
and was happily surprised when I could pick up several of the local VHF
communications systems operating here around 49 megaHertz, using just a
test lead from the multimeter as an antenna. Converters are no longer
required for all practical purposes, as modern HF receivers are
including extended tuning range up to the two meters amateur band.
Anyway, for those of you like amigo Scotty that are interested in VHF
converters, I may add that they are not too difficult to homebrew,
especially if you use solid state devices. A typical more modern
converter will use a high gain low noise MOSFET RF amplifier stage, a
double balanced passive mixer and a bipolar transistor oscillator. It
will be powered from 12 volts DC and when connected to even a low cost
modern digital receiver, will turn the resultant combination into a
rather nice VHF receiver, useful for monitoring 6 meters during the
summer sporadic E season, like the one we are happily enjoying right at
this moment.
Remember to tune set the receiver to scan from 50.0 to 50.3 megaHertz
where most of the activity on 6 meters is concentrated around the world.
QUESTION TWO, Came from Montego Bay in Jamaica, listener Randy, who
listens to our 9550 kilohertz Caribbean edition, tells me in his e-mail
that he wants to know more about the “non magnetic loop” antennas and
why are they so useful when used at noisy locations. Well amigo Randy,
standard one wavelength perimeter loops are not compact antennas, but
they are easy to turn around a single mast in any compass direction to
cancel noise sources, and above all, can be built very easily and at low
cost by anyone . The ultra simple one wavelength perimeter loop is a
perfect example of what I am talking about. It is built using a standard
household PVC covered number 14 wire, three home brew insulators and 75
ohms of TV type coaxial cable, and because it is going to be used as a
receive only antenna, I didn’t bother to try to match the 110 ohms
impedance of the loop to the 75 ohms coaxial cable. It takes less than a
couple of hours to complete. The full wave loop is not a MAGNETIC LOOP,
and it is capable of providing excellent reception from 10 to 30
megaHertz, but it also works quite well with powerful stations from 5 to
10 megaHertz. Amigo Randy, I am sending direct to you via e-mail the
complete , step by step building instructions for the one wavelength
perimeter loop, so that you can start building yours and then tell me
also via e-mail how it performs at your location.
The one wavelength perimeter loop is possibly one of the lowest cost
high performance antennas that exist.
QUESTION THREE, yes, one extra today to reduce the backlog a bit, well
question three, sent by listener Carlos here in Havana, he wanted me to
describe the design parameters for the low cost two element antenna for
the 2 meters amateur band. Well amigo Carlos, using standard TV antenna
elements aluminum rods, the small YAGI uses a split driven element of
980 millimeters, fed at the center with 50 ohm coaxial cable. The boom
is made from PVC pipe of the type used for water distribution, and the
reflector element is 1002 millimeters long and located at exactly 51
centimeters from the driven element. This antenna has around 4 dB gain,
a broad radiation pattern, is rugged and easy to build and will help you
to access distant repeaters that can’t be reached using the typical
handie-talkie helically loaded antenna, popularly known as rubber ducky
because they look like the tail of a duck wagging!!!
Again, here are the dimensions for the 2 element low cost, easy to build
YAGI for the two meters amateur band, the driven element is 980
millimeters long and split at the center, you may want to make it a
little shorter if you plan to use the antenna for the segment of two
meters between 146 and 148 megahertz. The boom of the antenna is made
from PVC pipe of the type used for high pressure water distribution, and
is one meter long, so that you can hold the antenna to any support from
the rear of the reflector element.
The separation between the driven and the reflector element is 51
centimeters, and the length of the reflector element is 102 centimeters,
that you can make a little shorter for the upper two megahertz of the
two meter band.
I feed this antenna with 50 ohm coaxial cable, and right after the feed
point, I wind 8 turns of the coaxial cable to the boom of the antenna to
make an RF choke... the cable is then fed trough a hole in the boom to
the rear of the antenna where it exits . I have made many of these
antennas, and found out that they provide excellent performance, and
when built using the above mentioned dimensions they are usually below
1.5 to 1 standing wave ratio even before any adjustments are made. They
can be adjusted for almost perfect standing wave ratio by sliding the
reflector element back and forth across the boom, and then leaving it
permanently at the spot that provides the lowest SWR. Remember to use TV
antenna rods or tubing, as the dimensions for my low cost two meter YAGI
just described are based upon the diameter of the typical TV antenna
elements.
Try to tune the antenna for minimum SWR using a VHF standing wave ratio
meter, but again, you can use the antenna directly without any
adjustments without fear of high SWR, by just carefully measuring the
elements .
And now amigos as always, at the end of the program, here is Arnie
Coro’s Dxers Unlimited’s HF propagation update and forecast…
HF propagation conditions are very poor during your local daytime hours,
but will certainly improve gradually after sunset in the northern
hemisphere.
Solar flux is hovering just above 70 units and the A index was at a nice
and low 3 units. The sunspot number Tuesday was 11, indicating a very
low solar activity.
The good news is that Sporadic E openings are going to continue to be
plentiful, surprising, interesting and challenging during the next few
days, so monitor the low band TV channels for them. If you have a 10
meters or 6 meters band amateur radio rig, keep it on during the time
that you are at home, keep them scanning from 28 to 28.5 megaHertz and
from 50 to 50.3 megaHertz for signs of openings, that in many cases will
be detected when automatic beacons start to come in as the opening
starts … See you all at the weekend edition of the program and don’t
forget to send me your radio hobby related questions, signal reports and
comments.. send mail to: arnie@xxxxxx, or Via Air Mail to Arnie Coro,
Radio Havana Cuba, and Havana, Cuba
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