Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited´s mid week edition for 1-2 April 2008
By Arnie Coro
Radio amateur CO2KK
Hi amigos radioaficionados !... You are certainly most welcome to the
mid week edition of Dxers Unlimited, our station´s radio hobby program
that is on the air twice weekly . I am Arnaldo, Arnie, Coro , radio
amateur CO2KK and here is item one of today´s show: Scientists
continue to try to forecast when the peak of solar cycle 24 is going
to happen, and they are also trying hard to forecast the actual value
of the period of maximum activity , that is the smoothed sunspot
number for the six months that will be considered to be the most
active of cycle 24. So far one only hears disagreements among the
world´s most prestigious heliophycisists ... and that difficult to
pronounce word, is the one used to call the solar scientists... In the
meantime , rumors are rumbling that already cycle 23, the present one
has achieved the unique characteristic of been a very long cycle by
all standards.
The tail end of cycle 23 has produced about the worst propagation
conditions on the HF bands remembered since the very low activity
cycle that took place during the first years of World War Two...
Second news item: The contest ionosphere booster effect worked once
again, and participants of the CQ Radio Amateur Magazine world
prefixes contest observed with big surprise how stations on the 10
meters band could be worked during the contest, when just a few days
before and with higher solar activity 10 meters was totally dead.
Sure, contests generate a lot of activity on the amateur bands , and
that activity in turns makes possible two way contacts on frequencies
that are little used during the solar minimum years. To me, the
presence of 10 meter band stations during the WPX contest period
didn´t produce a big surprise amigos, that was something that I was
expecting ...
Item three: A barebones ultra simple amateur radio station under test
at CO2KK , my ham radio station , has so far made possible several
nice DX contacts... The design philosophy of the barebones station was
to keep the parts count to a minimum, while not compromising its
performance. The group of Cuban radio amateurs that came together to
work on the project agreed that the simple station must be reaching at
least 10 watts , with a receiver sensitivity of one microvolt... The
station is to be used by beginners, that will be told how to install
an efficient 40 meters band antenna too... With the parts locally
available, the designers have done a good job, having to face the
difficulties derived from the lack of some specialized components,
cleverly replaced by recycled parts...
Stay right on this frequency or world wide web connection
ss Dxers Unlimited continues in just a few seconds after a short
station ID
..................................
This is Radio Havana Cuba, the name of the program is Dxers Unlimited
and now, let´s continue with the description of the ultra simple
amateur radio station. This is a modular station, with the
transmitter, receiver and power supply modules built and tested
Individually, before putting the station together. The best approach
is to start by building and testing the power supply, then moving to
the receiver, and finally assembling the transmitter.
The modular construction allows the builder to test upgrades to a
specific module, be it the transmitter, the receiver or the power supply.
You can even build separate modules, for example two or three
different transmitter configurations, that can be powered from the
same supply... by means of a simple interconnecting set of cable.
My favorite modular station setup at this moment uses the single band
approach, to keep things simple and easy ... The decision regarding
which band should be selected for best all around operation moves very
much in favor of 40 meters, with 20 meters in my opinion a good second
choice .
40 meters is normally open for DX during local evenings, when most
radio amateurs have time to operate, and at the present phase of the
solar cycle, 20 meters dies down just around sunset.
The receiver of this modular station is a rather straightforward
design, without any fancy additions, in order to use the least
possible number of parts. A single conversion superheterodyne receiver
with an intermediate frequency between 2 and 5 megaHertz seems to be
the most reliable and easy to build design.
The availability of low cost quartz crystals used for computer clocks
and other applications that have required mass production of crystals
of the same operating frequency, lends itself to the homebrewing of
some excellent bandpass ladder type crystal filters that show an
excellent performance. Adding a simple audio filter module further
enhances the performance of the receiver.
The first transmitter used in the modular station was originally
designed for CW operation only, but the second one had capability to
operate on double sideband too. A third upgrade now in operation is
capable of single sideband voice operation too.
Finally the power supply can be connected to the domestic home power
lines, and it also has the capability to act as an interphase with
full reverse polarity and overvoltage protection when connected to a
car, boat or any other 12 to 14 volts direct current system that may
be available.
No, this is not a miniature , compact ham radio
transmitter-receiver... it is in fact a very rugged, reliable, easy to
fix in case of breakdowns radio station that is capable of providing
excellent performance for both fixed and portable operation, and it is
specially suited for deployment during emergencies.
Maybe in the future, I will upgrade this design to a two band station,
keeping in mind that it is a very useful radio to have at hand during
the hurricane season here, because it is very economical on the
batteries, and has a much lower number of electronic components that
may break down , as compared to a factory built multiband transceiver.
Your comments , with ideas on how to improve Arnie Coro´s Emergency
Portable Amateur Station are most welcome amigos, send them to inforhc
at enet dot cu, again inforhc at enet dot cu or Via Air Mail to Arnie
Coro, Radio Havana Cuba, Havana, Cuba.
......
You are listening to the mid week program of Dxers Unlimited, when
solar activity is moving down again, as the three sunspot active
regions continue to move across the solar disc and no new sunspots are
in sight... Now here is our next section of the program, it´s the
Technical Topics, the number three most popular among listeners, after
ASK ARNIE, la numero uno
And the HF propagation update and forecast that is always in second
place according to your e-mail message and letters...
Today´s technical topic will be dealing with the repair of solid state
amateur radio transceivers, something that is becoming more and more
difficult, and almost next to impossible as manufacturers continue to
use more and more surface mounted devices ... As a matter of fact, the
repair of practically all of the amateur radio transceivers built
after 1990 or so, is only possible by sending the equipment to the
original manufacturer´s authorized dealerships, and even in that case,
many are returned to their owners not repaired or even more damaged
than when they were sent to be fixed. My personal opinion is that the
only way to fix the latest models of amateur radio transceivers is by
changing complete circuit boards, and essentially sending to the trash
can the boards that are removed. Transceivers built earlier in the
days of solid state devices history, are much easier to repair,
especially if you have previous knowledge of similar breakdowns... as
for example, the typical receiver failure of very poor sensitivity,
that can usually be traced to a bad front end active device, like the
dual gate MOSFET used for the RF amplifier stage of rigs like the
Kenwood TS520, 820 and 830 , just to give you an example. The MOSFET
devices , even when protected by internal diodes, fail after a nearby
lightning strike, that doesn´t necessarily has to be right next to
your property.
Loss of receiver sensitivity is quite evident, and replacing the
MOSFET is a quite straightforward repair job, except that nowadays the
exact replacement parts are becoming quite difficult to find...
Amigos, let me add that homebrewing your receivers, transmitters and
transceivers , as well as amateur station accessories is not only a
very nice aspect of our hobby, but it also provides immunization
against expensive equipment breakdowns that simply can´t be repaired !!!
..................
Now, here is nice news for the VHF and UHF radio amateur enthusiasts,
station T42UJC, a special even station will be on the air on six and
two meters plus 70 centimeters, from atop a 12 story high building
very near the northern coast of Cuba . The special event station will
also be active on the 20 meters HF band. Here is now the announcement
sent by CO2OJ, Oscar Morales Junior, who will be in charge of this
interesting ham radio activity, Oscar tell me ..Our VHF Group will
activate an special station (T42UJC) from april 3 to april 5. The
station will be here in Habana, in a 12 floor building, just in front
of the Ave. Malecon, a little more than 50 meters from the shore with
more than 120 degrees free view over the Golf. T42UJC will be active
on 6m, 2m and 70 cms ssb. 100 watts in 6 and 2m and 25w in 70 cms.
Vertical antemna in 6m, a 12 elements yagi in 2m and a 17 elements
yagi in 70 cms. Will be active also in 40m and 20m. In 20m mostly in
RTTY and PSK31. So there you are, a good chance to add a new prefix to
your collection, and for many of the newcomers to amateur radio,
working Cuba on 6 and 2 meters is also very nice too... So be on the
lookout for T42UJC, from April 3 to April 5, and send your QSL
requests to T42UJC Post Office Box One, Havana, Cuba...
And now amigos as always at the end of the program when I am here in
Havana and can make the solar optical and radio observations here is
Arnie Coro´s exclusive and not copyrighted HF plus low band VHF
propagation update and forecast... Solar flux now moving down again,
and the period of better HF propagation is just coming to an end...
Sunspot count now below 20 and the solar flux again below 80 units, so
the daytime maximum useable frequency curve will again show a very
slow rise and will be reaching a much smaller peak... I expect some
nice tropospheric ducting across the Gulf of Mexico during the next
several days, an excellent opportunity for radio amateurs in Mexico
and the South of the USA to work the special event VHF and UHF station
T42UJC starting Thursday and until Saturday.
I hope to have have enjoyed this program and will be listening to our
weekend edition Saturday and Sunday UTC days amigos ...And don´t
forget to provide me with your valuable opinions about the program ,
any radio hobby related questions you may have for our ASK ARNIE
section of the show, and your QSL requests... send mail to inforhc at
enet dot cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba ,
Havana, Cuba