Dxers Unlimited

Dxers Unlimited 24-25 April 2004

By Arnie Coro

Radio amateur CO2KK




Hi amigos radioaficionados , around the world and also now circling the world aboard two spaceships
! I am Arnie Coro, radio amateur CO2KK , your friend in sunny Havana now ready to share with you
this weekend edition of Dxers Unlimited, a radio hobby program for both beginners and experts !!!
Here is item one . Solar flux has hovered near the magic 120 level,providing us with nice
propagation conditions on the HF bands until Friday, when at least one solar flare and a high speed
stream of particles brought by the solar wind spoiled what was until then a very nice week for
Dxing. A photograph of the Sun shows a new active sunspot region just turning around, and this may
increase solar activity a bit during the next few days. Solar optical observations also show a
coronal hole that in a few days may become the source of more geomagnetic disturbances. As we enter
the last week of April be on the lookout for the first early signs of SPORADIC E openings, that can
easily be detected by monitoring , with an external antenna of course, television channels 2 and 3
in the Americas.

Item two: Our national hurricane emergency drill is just around the corner, and all Cuban radio
amateurs that participate in this national effort organized by the Cuban Federation of Radio
Amateurs are getting ready for the field practice day, that is held during one of the first two
weekends of the month of May, just before the official Hurricane Season starts on the first day of
June. One of the reasons why amateur radio exists is precisely its unique ability to provide
emergency communications links under even the most difficult circumstances.something well
appreciated by governments all around the world !

Item three: An intermittent fault is one of the most difficult, it not THE most difficult type of
fault to repair on any piece of technological equipment, from a simple radio to a huge passenger jet
aircraft. Today's Dxers Unlimited's technical topics section will be reviewing some unique but easy
to put into practice fault finding and isolation techniques that have proven to be very effective
indeed. We will also broadcast our popular ASK ARNIE section of the show, Tips and Techniques and at
the end of the program our exclusive and not copyrighted HF plus low band VHF propagation update and
forecast !

Standby amigos for just a few seconds , when Dxers Unlimited will continue after this short musical
intercut !

...

Si amigos, this is Radio Havana Cuba, and reception reports coming from North America are telling me
that our 11760 kiloHertz transmitter is providing very good reception during three different
schedules, in the morning from 11 to 15 UTC, then during the local afternoon here in Havana,
starting at 21 hours UTC and later in the evening, we broadcast in Spanish from 00 to 05 UTC and
then switch to English from 05 to 07 UTC .

Send your signal reports of our 11760 kiloHertz transmissions to arnie@rhc.cu, and for those of you
who want to know what we are using on that frequency, its one of our brand new 100 kiloWatt
transmitters using pulse step modulation technology, and a full wave dipole that is beaming to 160
and 340 degrees, as to provide a broad coverage of North , Central and South America with a single
antenna.

Now here is our SPECIAL FEATURE for today, fault finding , especially locating intermittent problems
that are the radio and electronics technicians and engineers biggest headaches. Have you ever
experienced an intermittent fault on a technological complex piece of equipment. You surely have
seen your car , the home stereo, the TV set or even the microwave oven or kitchen blender start
doing funny things due to an intermittent fault ! Sure, the fault is there for a while, then it
mysteriously it goes into a self clearing condition, that according to many of my aircraft pilot
friends is the most dangerous thing that can happen while in flight.

Radios don't fly , but they can surely suffer from intermittent faults that cause a lot of
trouble.as a matter of fact sometimes equipment is discarded after several repair persons go trough
the standard routines and fail to find the cause of the fault.

Today here at Dxers Unlimited, I will give you a few tips on how to find an intermittent fault on
electronic equipment.. Here is tip number one : FREEZE IT, yes, find a canister of CO2 gas,
especially made for this purpose and spray the solid carbon dioxide snow to different parts of the
circuit board. amazing as this may sound, it does work quite well indeed. not too long ago, using
the CO2 carbon dioxide ultra fast cooling fault finding technique I was able to fix an expensive
amateur radio transceiver that had defied so of Cuba's best and most highly qualified radio repair
technicians and engineers. By spraying parts of the different circuit boards selectively I was able
to locate the area of one of the boards where the problem was, as the fault cleared every time that
area was sprayed with the carbon dioxide snow !!!It took just a few minutes to desolder several
components, replace them with new ones and test the transceiver, to find that everything was back to
normal. By the way the problem was caused by a defective electrolytic capacitor that was opening up
intermittently !!!

TECHNIQUE NUMBER TWO: Use a VARIAC or variable auto-transformer in two different modes. MODE ONE,
connect your equipment with the intermittent fault to the VARIAC and set the output voltage to about
85 volts, and see what happens. Very often lowering the AC power line voltage will clear the fault,
so you can then look carefully at the components that are closer to the DC voltage bus bar. Then
MODE TWO, goes all the way around, that is you raise the AC line voltage to 130 volts or so, but do
that very carefully, as I have seen a faulty intermittent component go UP IN SMOKE immediately after
applying 135 volts AC to the piece of equipment under test !!! Using higher than normal AC power
line voltage for test purposes must be done very slowly and carefully, raise the autotransformer's
output little by little and keep a close watch of the current used by the equipment by means of a
digital multimeter set for measuring the AC current taken by the set under repair. Sometimes you
will see a sudden jump in the AMMETER indication, that will signal when the defective component goes
into total failure, something that is a lot more easier to find and repair than the headache causing
intermittent fault !!!

FINALLY , another tip for fault finding and repairing intermittent problems. and this one requires a
lot of patience but seems to work in many instances. According to recent electronic industry
reports, about 80 percent of today's modern equipment fail due to bad soldered connections. so you
won't loose a lot by just going trough the printed circuit boards with a nice soldering iron and
high quality solder, reviewing each and every connection, but I warn you, this has to be done with
extreme care , because you can also create a new problem if you accidentally bridge solder between
two connecting points !!! The review the soldering technique has proven to be particularly effective
on some amateur radio transceivers built by Kenwood in the late nineteen eighties and early nineteen
nineties.of which you may still find some lying around just waiting for someone with enough patience
to attempt this type of fault fixing procedure !!!

Si amigos , yes my friends , oui mes amis , self clearing faults are a big headache, but they can
also be turned to your advantage , if you happen to catch a good deal on a pice of equipment with
such a problem that you may be able to repair and bring back to life !!!

...




Si amigos ! Ask Arnie is THE most popular section of this program, and I receive lots of radio hobby
related questions every day via e-mail and twice weekly when we go to the Post Office Box to pick up
the mail. Here is today's question,sent by listener Roger in Jamaica. Dear Arnie, I live in downtown
Kingston, Jamaica and my short wave reception is difficult to say the least. The noise level is very
high. Do you have any ideas how to improve my reception ?Well amigo Roger, you are a very likely
candidate for a magnetic loop antenna. A simple receive only magnetic loop, made from a length of
RG213 or RG8Ucoaxial cable, and using a standard AM broadcast band receiver variable capacitor for
tuning, will improve your reception dramatically, because it will pick up much less noise. The
signal to noise ratio of your receiving setup will be better, so you will be able to enjoy much
nicer short wave reception.

I am sending to you via e-mail the easy to understand graphics and text describing a simple receive
only magnetic loop that can be built using locally available materials and at very low cost. Please
e-mail me when you complete the antenna and start using it. I am sure that other Dxers Unlimited's
fans around the world would like to hear about your results with the magnetic loop !

And now amigos as always at the end of the program here is our exclusive and not copyrighted HF
propagation update and forecast.. Solar flux still hovering around 120 units but seems to be moving
down a bit, only to recover after Monday or Tuesday, when another active sunspot region should
rotate into view. High speed solar wind from a coronal hole may be reaching the Earth by Tuesday UTC
day, with possible disruption of HF circuits at high latitudes. The sporadic E skip season is also
about to start, and my forecast calls for E skip openings to start as early as Wednesday ! Be on the
lookout for TV and FM band DX, and for radio amateurs, 6 meter band openings will begin to become
more and more frequent from now on !

See you all at the mid week edition of the program amigos, and don't forget to take a little time
and send your signal reports and comments about the program to arnie@rhc.cu, or VIA AIR MAIL to
Arnie Coro,Radio Havana Cuba, Havana, Cuba