Dxers Unlimited
Dxers Unlimited for 23-24 December 2003
By Arnie Coro

Radio amateur CO2KK




Hi amigos radioaficionados, wishing you all a very nice end of the year 2003, and a very prosperous
2004... Just back in Havana a few hours ago after a very interesting trip to Brazil, where I
attended a scientific conference dealing with the preservation of the world's digital heritage, one
of the topics I teach about at the University of Havana's School of Social Communications, and of
course that I took my portable radio, and a wire antenna to listen from Rio de Janeiro, where I
stayed for almost a week.

It was nice to pick up some short wave stations that are seldom heard in Havana with such quality,
as the Radio Argentina al Exterior15345 kiloHertz frequency kept on the air in an act of devotion to
radio by a group of engineers at the General Pacheco transmitter site, that according to what I was
told by an ex Radio Argentina al Exterior Director General, looks more like a radio museum than an
actual transmitting station.... I also heard some nice DX from Africa and Asia with surprisingly
good signals using just an indoor wire antenna... More about my trip to Brazil later in today's
midweek edition of Dxers Unlimited, your favorite radio hobby program,reaching you via short-wave
and also via our streaming audio connected to the world wide web...

Now item two: My optical observations of the Sun done at around 15 hours UTC Tuesday, that's 10 AM
LocalTime in Havana, showed two rather active sunspot regions, that according to their size and
development could generate class M solar flares during the next several days. The actual number of
sunspots have increased during the past day or so, and there is also a well defined coronal hole in
sight... Solar flux is now around 140 units and the actual sunspot count is around 150 or so. As we
have just passed the winter solstice on Sunday, from now on each day will have a little more time of
solar illumination until we reach the spring equinox...

Winter propagation conditions are now very well defined, and that calls for a rapid drop of the
maximum useable frequency curve as soon as the Sun sets at your location. For radio amateurs this
means that the 30, 40 and 80 meter bands are going to be the place to be during nighttime operation,
and if you happen to have a nice 160 meter band antenna, then you can enjoy working DX on top band
too...

As always when I am at home here in Havana, we will feature at the end of the show Arnie Coro's
Dxers Unlimited's HF propagation update and forecast...

Other items here today include our technical topics section, the number one most popular section of
the show, YOU HAVE QUESTIONS, and a few comments about digital communications... stay tuned for more
radio hobby related information coming up in a few seconds.

I am Arnie Coro in Havana...

......

This is Radio Havana Cuba, the name of the show is Dxers Unlimited.... and here is now our technical
topics section... today I'll be telling you about a big problem that is now expanding around the
world... it has to do with bad electrolytic capacitors, not one or one thousand , but hundreds of
thousands of such capacitors that were manufactured some time ago with a wrong formula for the
electrolytic paste that is required by such components. The bad capacitors have spread trough the
electronics industry, and many of them ended up soldered to computer motherboards, that are now
failing catastrophically when the electrolytic capacitors either produce a dead short, or an open
circuit. Several radio manufacturers apparently have also used those bad electrolytics and likewise
the radios built with them are also failing at an alarming rate... So here is Arnie Coro's advise,
before buying a new computer or a new radio, check very well about the failure rate of the equipment
in order to avoid the possibility of having to deal with those bad electrolytics... And don't even
think about changing them , as the time and trouble required would not be worth the effort, as you
will end up with a piece of equipment with many areas of the main board heated to high temperatures,
something that is not convenient at all....

And here is another tip regarding electrolytic capacitors... they will last a lot longer when their
operating environment temperature is below 25 degrees Celsius... so, try to keep your radios,
computers and all electronic equipment operating at temperatures not higher than 25 degrees Celsius
amigos, they all will last longer when kept operating in such an environment... And before I forget,
the ideal relative humidity range is from 40 to 70 percent ....

Electronic equipment in general show a marked tendency to last longer when operated between 10 and
25 degrees Celsius and relative humidity range between 40 and 70 percent....

.......

Si amigos, yes my friends,oui mes amis, 2003 is coming to an end, and it was a very interesting year
from the point of view of many scientists that are following the solar cycle with the best ever
available instruments to monitor the activity of our nearest star. During the year 2003 there was a
very important event, a solar flare that according to some sources was the most powerful ever
monitored since the days of Galileo Galilei... and we were really fortunate that the solar active
region that generated such a powerful outburst of energy was located in a position that sent out the
stream of particles from the solar corona away from Earth. A Cuban scientist told me recently that
if the supermega flare had erupted from a solar region in a geoeffective position, at this time we
would still be trying to launch replacement satellites for all of those that would had certainly
failed when impacted by the super powerful radiation and stream of charged particles...

Now, here is our very popular YOU HAVE QUESTIONS ,and your amigo Arnie tries to answer them, on the
air , and on the web and of course, direct to you via e-mail.... There are several questions to be
answered today... Numero uno, the number one question, from Rajiv near Bangalore, the garden city of
India... Rajiv wants to know if he can replace electrolytic capacitors used in an old vacuum tube
receiver that he is trying to revive, using higher capacity ones that he happens to have available.

Well amigo Rajiv, here is my advice... for capacitors located in areas of the circuit where they are
used as filter capacitors to smooth the current provided to the electrodes of the vacuum tubes, you
can certainly used larger capacity ones without any problems at all, but the reverse is not true...
For example if you have to replace a 100 microfarads at 300 volts DC electrolytic that is used to
filter the voltage provided to low signal level audio preamplifier stages, then you can use there a
150 microfarads or even a 200 microfarads capacitor without any problems... BUT, changing the 100
microfarad capacitor to a 40 microfarad one may work, or may not work...If you have no choice and
there is no other capacitor at hand, you can try and see if it works or not... In many cases design
engineers used larger capacitors than those really required because they happen to be available to
the manufacturer, or in order to provide a margin of safety when the capacitor's actual terminal
capacitance went down after years of use, a still unresolved problem with electrolytic capacitors...
So amigo Rajiv, start to change the capacitors, do it on a one by one routine, and check the actual
operation of the equipment each and everytime you change a capacitor....I have revived here lots of
radio and other electronic equipment by following that procedure... Any piece of electronic gear
more than 15 years old is a likely candidate for a radical maintenance operation that must include
changing ALL THE ELECTROLYTICS !!, SI, YES, OUI, you change them all , and the life expectancy of
the equipment will multiply several times!

.........

You are listening to the mid week edition of Dxers Unlimited, and here is a preliminary answer to a
question sent in by several listeners that pick up our broadcasts on 6000 kiloHertz to North
America... The noise that is now heard at some hours on that frequency is apparently coming from a
transmitter located in Sackville, Canada. The transmitter is broadcasting using the DRM, Digital
Radio Mondiale standard , and its bandwidth is according to what I have heard here in Havana well
beyond the DRM standard's maximum bandwidth. As DRM is a completely new broadcasting technology that
requires transmitters to be extremely linear in their operation, I was not surprised when my e-mail
box was full of complaints about the DRM incompatibility problem on the 6000 kiloHertz
frequency...Now we must wait and see if engineers at the Sackville , Canada, transmitter site become
aware of the problem and are able to adjust the equipment so that it will not use up such a large
bandwidth that causes problems to stations operating on frequencies near to the DRM broadcasts.

Any reports about poor reception on 6000 kiloHertz caused by a rushing sound coming from the DRM
broadcasts from Canada will be most appreciated... send them to arnie@rhc.cu, or VIA FAX to the
following number , country code 53, then dial 78785810, again our FAX number is country code 53,
then 7-8-785810...

If you have any news or information about DRM Digital Radio Mondiale tests in progress, it will also
will be most appreciated, as many broadcast engineers around the world are concerned with the real
life compatibility of DRM with current AM modulation short wave broadcasts... Remember, any rushing
type sound heard on top of our 6000 kiloHertz frequency may be coming from the DRM transmitter
operating nearby and the more we learn about the problem will help to try to solve it so that you
can continue listening to Radio Havana Cuba's 6000 kiloHertz frequency the way you have always heard
us at this time of the year...

And now amigos, as always at the end of the show , here is Arnie Coro's HF plus low band VHF
propagation update and forecast...

Solar activity will continue to be at LOW levels,but there are two active sunspot regions now in a
rather geoeffective position and capable of producing M class flares. If flare activity increases,
we may see more geomagnetic disturbances during the next several days... Expect starting on
Wednesday rather nice typical winter time propagation for Europe, North America and the Caribbean,
with daytime maximum useable frequencies reaching even up to the 10 meter bands during brief
periods... Solar cycle 23 continues to decline, but it may produce yet another surprise upsurge in
activity at anytime during the next three months !. See you all at the weekend edition of the
program, and I do hope that you enjoy very nice HF reception during the holidays amigos !