Dxers Unlimited's mid week edition for July 1-2 2003

By Arnie Coro

radio amateur CO2KK




Hi amigos radioaficionados ! Welcome to the mid week edition of your favorite radio hobby program
amigos ! I am Arnie Coro, your host here in Havana, inviting you to share with me the next 17
minutes of on the air and on the web time. Here is item one: HF propagation conditions continue to
suffer from almost permanent high speed solar wind plasma disrupting the Earth's magnetosphere.
Those of you located at higher latitudes have certainly gone trough really tough times because the
higher the latitude the worst the effects of the geomagnetic disturbances... More about the HF
propagation conditions for the rest of the week at the end of the show. Item two: CO-0-US and
T4-2-FD, the two Field Day entries from Cuba this year ended up with quite a good number of
contacts, plus many bonus points , but poor propagation made the Pina Colada Contest Club joint
effort with the Cuban Federation of Radio Amateurs unable to reach the number of two way Field Day
contacts that they had expected. Nevertheless, the six American and four Cuban permanent operators,
plus the several part time participants worked very hard to make possible the first ever joint
Cuba-USA Field Day station. Monday evening at the headquarters of the Cuban Federation of Radio
Amateurs I attended a farewell dinner for the American participants, and had the opportunity to tape
very nice interviews with the group of USA radio amateurs that will be featured in our Dxers
Unlimited's weekend program... Item three: Among the antennas I saw at the CO-0-US and T4-2-FD site
was a very nice super lightweight MOXON RECTANGLE for the 15 meter band, that unfortunately did not
saw much action, as the 21 megaHertz ham band was closed for most of the 24 hours that the station
operated... More about the lightweight super-portable version of the MOXON RECTANGLE that the Pina
Colada Constest Club brought for the contest later in today's edition of your favorite radio hobby
program, Dxers Unlimited with your's truly Arnie Coro at the microphone...

Item four: Among the many topics that we talked about when visiting the contest station on Saturday,
was how these stations help radio clubs to better organize their emergency fast response teams. We
also talked about digital communications modes and how they will play a more important role in the
future. While we were at the Guanabito tourist resort site, Tropical Storm Bill was forming in the
Gulf of Mexico, reminding all of us how important amateur radio emergency readiness for our two
countries all along the Hurricane season.

Margarita Delgado is my sound engineer and producer, I am Arnie Coro in Havana back with you in just
a few seconds , after a short musical interval..

......




You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and it's on the air
twice weekly with the most up to date HF short wave and low band VHF ionospheric propagation
forecasts, and sometimes we also add tropospheric ducting forecasts too... Now let's talk once again
about the MOXON RECTANGLE single band antenna . The Pina Colada Contest Club's version of this
unique compact antenna uses a supporting structure made with fiberglass fishing rods, and the
antenna two elements are made using common plastic PVC insulated wire of the type used for wiring
homes. The antenna weights just a few pounds, and from an electrical point of view is as efficient
as a full size two element Yagi, and it also has an advantage over a conventional Yagi, because the
MOXON RECTANGLE is capable of providing an extremely high front to back ratio. The high front to
back ratio is extremely convenient for some contest stations, as they can move the antenna in order
to reduce interference from other stations located on the back of the main beam. According to the
measurements performed by several antenna experts, the MOXON RECTANGLE's actual gain over a dipole
is very near 4 decibels, but by placing the antenna at a height above ground of no less than three
quarters of a wavelength, it produces a very low take off angle ideal for Dxing.

One problem that the MOXON RECTANGLE built with insulated wire had, was that the measurements showed
higher than expected standing wave ratio at the design frequency, something that was solved once the
builders remembered that insulated wire has a different velocity factor than bare copper wire...
After readjusting the length of the two elements, the antenna's standing wave ratio went down .
Another thing the contest team found out, was that the MOXON RECTANGLE's 50 ohm coaxial feedline did
require proper decoupling . This was achieved by using a certain number of ferrite toroids, that
effectively decoupled the out of balance currents from the feedline. We continued to talk about the
compact lightweight MOXON RECTANGLE single band antenna for a while, and among my suggestions to the
team was to use a one to one balun at the feedpoint, so that there will be no need to use the
ferrite toroid rings By the way for those of you that may be interested in building a MOXON
RECTANGLE, I have a nice little WINDOWS freeware program that calculates all the MOXON's parameters
in a few seconds... Just send your request for the MOXON RECTANGLE SOFTWARE to arnie@rhc.cu, again,
my very easy to remember e-mail is arnie@rhc.cu .

Other antennas used at the contest site for CO-0-US and T4-2-FD included a nice 40 meter sloping
dipole, a horizontal 80 meter dipole installed between the two higher telescopic masts, and several
other Yagi two and three element beams, plus a multi band vertical. For local VHF contacts on the
two meter band, another vertical gain antenna was installed too. Field Day and real life emergency
stations have many things in common, among them the fact that the antennas deployed should be well
installed in order to stand possible high wind conditions . At the Guanabito site of our Field Day
station a really powerful thunderstorm knocked down one of the antennas just at the end of the
contest, reminding everyone of the importance of proper use of guy wires and anchors !. More about
the joint CUBA-USA Field Day Station next Saturday and Sunday UTC days during our Dxers Unlimited's
weekend edition amigos !!!

.........

Short wave listening is many times the gateway into amateur radio, but many short wave listeners
continue to enjoy that aspect of the hobby after they become licensed amateur radio operators.
Listening to short wave broadcasts is a nice way of learning more about the world in which we live
amigos !!!

Now item five of today's program: A visit to Arnie's workshop... Well the workbench is pretty
crowded as usual, but the most interesting thing happening at my workshop, is the development of yet
another ultra simple ham radio transmitter. This one was designed so that Cuban amateurs may go on
the air immediately after taking their ham radio license test. The Cuban radio rules and regulations
require that you install a complete station capable of two way communications , in order to issue
the station license, which is in our case separate from the operators license... So for many
newcomers that have already taken the test, the problem is how to build a simple station that will
put them on the air as soon as possible. And that's exactly what I am doing right now at my
workbench, giving the finishing touches to a very simple, yet effective low power transmitter and
receiver. The set uses hybrid technology, that meaning that I have used both solid state and vacuum
tube components, because we still have here lots of brand new in the box vacuum tubes that can be
obtained either very cheaply or at no cost at all. The little rig puts out about 10 Watts on CW, and
the receiver has a sensitivity of about 5 microvolts, parameters that are more than adequate for a
40 meter band amateur station. The receiver is a REGENERODYNE, and that makes it very stable and
easy to use.... the front end of the receiver uses a 4 megaHertz computer crystal for the local
oscillator, and the regenerative receiver's second detector tunes from 3 to 3.1 megaHertz. giving a
very nice bandspread. This is an almost minimum parts count radio, that I expect to become very
popular among the many young people here that are taking their amateur radio license test this
coming Saturday all over the Cuban archipelago !!! It's a nice combination of solid state and vacuum
tube technologies optimized for maximum reliability and ease of construction by the newcomer,
although I would prefer that these transceivers be built under the supervision of more experienced
amateurs !!!!

......

This is Dxers Unlimited's mid week edition and here is item SIX : While at the workshop , I realized
how important it is to have proper illumination of your workbench in general, and a special spot
higher intensity light for the area where you are actually working. Another important part of the
well equipped electronics workbench is a magnifying glass, needed to be able to see those miniature
circuits better. I have obtained excellent results with non prescription positive diopters
eyeglasses... On one of the workbench drawers I keep three of them, a pair of PLUS TWO DIOPTERS for
general work, a pair of THREE DIOPTERS for more amplification and the PLUS FIVE DIOPTERS non
prescription eyeglasses that have helped to find so many problems , especially when attempting to
fix printed circuits that have the traces very near to each other.. Just a few days ago, a ham radio
friend's computer went dead, he brought the motherboard to my shop and we found out, thanks to the
PLUS FIVE DIOPTERS eyeglasses that the battery had leaked some nasty fluids, that in turn had caused
severe corrosion of several circuit traces... one of the tracks was totally damaged, and we
recovered the motherboard after a very extensive clean-up job and replacing the corroded traces very
carefully with very thing wires... My friend is now back on the air using the PSK31 digital ,
keyboard to keyboard mode thanks to that hour and half repair job !!!

And now amigos, just before going QRT , here is Arnie Coro's Dxers Unlimited's HF propagation update
and forecast.... Sunspot number reaching 160, at the same time that the 10.7 centimeter yardstick
solar flux is hovering around 130 units.

According to Cuban solar expert Angel Gonzalez Coroas, there is one active sunspot group of interest
, but solar activity is expected in general to start going down as the 27 day subcycle continues.
Expect good local nightime propagation in the frequency range between 10 and 16 megaHertz. Stations
operating between 5 and 10 megaHertz will experience higher atmospheric noise levels, making
reception more difficult... So radio amateur should enjoy nice evening contacts

on 30 and 20 meters, while the 40 meter band will provide DX later in the evening. No really big
solar flares are expected for the moment. Low band VHF should benefit from more sporadic E layer
openings . See you all at the weekend edition of Dxers Unlimited Saturday and Sunday UTC days . AND
don't forget to send your comments about the show and QSL requests as well as your radio hobby
questions to arnie@rhc.cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba.