Dxers Unlimited

Dxers Unlimited's weekend edition for 10-11 April 2004

By Arnie Coro

radio amateur CO2KK

Hi mis amigos radioaficionados around the world and in space !!! This is the weekend edition of your
favorite , listener oriented and technically minded radio hobby program, coming to you via shortwave
and also via streaming audio on the World Wide Web from www.radiohc.cu, I am Arnie Coro, radio
amateur CO2KK, your friend in sunny, beautiful Havana, where we are enjoying excellent tropospheric
ducting propagation on the VHF, UHF and Microwave bands... Way out there, 93 million miles away, our
nearest STAR, amigo SOL, is now taking a break, and the actual sunspot count has gone down to around
30... The active sunspot region that generated most of the interesting activity during the past few
days is now loosing steam, so I expect a very low sunspot count and a diminishing solar microwave
energy flux during the next seven to ten days... More about HF, VHF, UHF and Microwave propagation
later, at the end of the program... Item two: Listeners letters provide instant feedback about the
show's content, new ideas, and very interesting radio hobby related questions that keep yours truly
really busy the whole week, and be aware that Dxers Unlimited, Breakthrough the science show, En
Contacto's propagation report and daily science technology and the enviroment at Radio Havana Cuba
are not my only duties... I do spend a lot of time every week teaching, and that amigos, is a very
rewarding activity, as you do learn a lot while preparing your lessons !!! Listeners from all around
the world write to Radio Havana Cuba's Dxers Unlimited and recently I decided to make a poll of the
show's most listened sections... As expected ASK ARNIE was once again LA NUMERO UNO... the most
popular section of Dxers Unlimited , closely followed by our exclusive and not copyrighted HF PLUS
propagation update and forecasts that according to the e-mail messages, postcards and letters,
really helps you all to catch nice DX sometimes, to optimize your band plans for a contest, or to
simply stay away from the radio and homebrew some more equipment when propagation conditions take a
turn for the worst !!! Item three: ASK ARNIE, today will be answering two questions, then it will be
followed by TIPS and TECHNNIQUES, a new Dxers Unlimited's section that is winning listeners at a
fast pace, and as always at the end of the program the propagation information that today will be of
a more general nature, as the show had to be taped on Friday due to a conflicting work schedule on
Saturday , and for those of you that will surely ask, YES, I do have to work ALL SATURDAYS amigos,
but not on Sundays !!! Stay tuned for more radio hobby related information, coming to you , with
love, from Havana...

I'll be back in a few seconds , after a short musical intercut

....

The name of the station is Radio Havana Cuba, we are on the air since 1961, providing to our
listeners the best possible programs about Cuba and the world amigos... Here is now ASK ARNIE for
today... The first radio hobby related question came from a country where Dxers Unlimited has a
massive audience, according to the e-mail messages, postacards and letters that I receive here every
week... Yes , its Canada, where the short wave listening hobby seems to have many followers... The
question was sent by Dxers Unlimited's listener Mark, from Toronto... He ASKS ARNIE... what is a
TUNIPOLE antenna ... because he recently visited an AM broadcast station, where the chief engineer
told him that they had recently changed their antenna to a TUNIPOLE... Mark then adds that he sees
exactly the same tower that has been there for years... Well amigo Mark, sure, the tower is the
same, but the antenna system was changed by the station's engineers to a very different
configuration. The TUNIPOLE is a commercial name for what is known in radio engineering as a
GROUNDED FOLDED MONOPOLE antenna... And the main reason the station you visited changed their
antenna configuration is that they almost surely had to upgrade to a new solid state transmitter.
The TUNIPOLE or more properly speaking GROUNDED FOLDED MONOPOLE ANTENNA, provides additional
protection against lightnning that is badly needed by today's third generation solid state
transmitters... The traditional vacuum tube power amplifier transmitters were much more tolerant to
voltage spikes generated by lightnning than their solid state equivalents of today... I have seen a
very nice second generation pulse duration modulation AM broadcast transmitter go off the air with
all its power modules dying instantly after a the series fed antenna took a direct hit from
lightnning... YES, sure, solid state transmitters are the way to go, no doubt, they save a lot of
energy and replacement parts are available at very low prices, but so far no one has found how to
really protect them from lightnning when they are connected to an insulated tower... So amigo Mark,
that's part one of my answer, now part two... the AM broadcast station you visited will also benefit
from converting their series fed insulated base antenna to a GROUNDED FOLDED MONOPOLE , because from
now on they can rent tower space to other users of the radio frequency spectrum, a source of extra
income to the station that will help AM broadcasters to balance their budgets. It's no secret that
in many countries AM broadcasting stations are loosing audience to FM stations, so by renting their
grounded towers to cellphone operators, for example, they can keep themselves on the air !!! A
typical 100 meters high AM station tower makes an excellent support for cellphone and other
commercial communications systems that can then save money by renting space on an existing site,
rather than having to make a completely new installation from scratch... Amigo Mark, radio is a very
complicated business, and tower space renting is becoming more and more important at a worldwide
scale, by the way, many high tower operators graciously provide tower space for amateur radio
repeaters in what could best be described as a very good public relations act. Now question number
two.. it came from South Africa, where we are building up an audience according to the
correspondence department here... Listener Mumbele from Cape Town, tells me that he is picking up ou
6000 kiloHertz broadcast for just a few minutes every day, on what seems to be a very short band
opening... Mumbele wants to know if this has something to do with what is known as GRAY LINE or
TERMINATOR LINE propagation... Well amigo Mumbele, I will have to take a look at the time of the day
here in Havana, and the time of the day in Cape Town that this is happening... GRAY LINE or
TERMINATOR LINE propagation happens when two points of the Earth are touched roughly at the same
time by the line that separated day and night... and YES, it does enhance propagation a lot... As a
matter of fact, many radio amateurs used terminator line propagation in a routine fashion to work
DX... By the way amigo Mumbele, you may want to give a try to our streaming audio still under test
at www.radiohc.cu...

.....

This is the weekend edition of Dxers Unlimited, coming to you from Radio Havana Cuba, and let me
reiterate that the show was taped on Friday, so our propagation information will not be able to
provide for any last minute event adjustments, although, I think that according to the present state
of solar activity the probability of a large solar flare happening is very low... Now here is our
TIPS AND TECHNNIQUES section of the show, one that is becoming really popular with all of you
according to the most recently received correspondence amigos... Several listeners wrote telling me
about their success with the homebrew microphones, and that they were really pleased with the audio
quality obtained from them... Gary from Indiana , USA, says in his e-mail that he is now collecting
broken cellphones in order to be able to make several more of the homebrew microphones for three of
his other transceivers... He tested a microphone element from a NOKIA cellphone that was damaged
when it was actually crushed by the tires of a car, that by miracle left the microphone undamaged...
Gary tells me that his two meters mobile FM transceiver sounds much better now, and that what he
actually did was to remove the microphone capsule from his rig's mike and replace it with the NOKIA
cellphone microphone element, leaving everything else untouched ... Si amigos, yes my friends, out
mes amis, as you all know, radio is hobby that can be enjoyed on a shoestring budget and that also
helps to keep the environment clean by recycling !!! Second part of TIPS and TECHNNIQUES... when a
radio receiver has not operated for a long time... don't just plug it in to the AC power line...
Bring it back to life slowly , by using one of the two following techniques... Connect the radio
that was in long storage to a variable voltage transformer, also known as a VARIAC, and set the
transformer for 25 volts AC output... keep the radio operating at that voltage for about 24 hours,
then go to 50 volts, and keep it there for 12 hours, step three is taking the operating voltage to
75 volts AC and keeping it there for 6 hours... Then you run the radio from 100 volts and turn it on
to see what happens... It is likely that it will make a nice comeback into useful life if there are
no damaged components... You can benefit by monitoring the AC power line current that the radio is
taking by means of a digital multimeter set for AC current measurement... This step by step method
has proven to be very effective for me, and has helped to detect bad electrolytic capacitors before
they really go up in smoke... By the way, if you are doing this procedure to an old vacuum tube
radio, it is a very good idea to do a total , comprehensive visual inspection of the receiver ,
clean the dust and accumulated debris, and then replace ALL THE ELECTROLYTIC and PAPER BYPASS
CAPACITORS, before plugging in the radio to the AC power line !!!

More recently built solid state receivers of the so called first generation, dating back to some 35
to 40 years ago will usually come back to useful life too, but replacing the electrolytic capacitors
will not be as easy as with the older vacuum tube receivers because of the use of very compact
layout of the printed circuit boards...

TIP NUMBER THREE for today... If you want to use a loudspeaker instead of headphones for listening
to CW Morse Code signals, use a small speaker, one between two and three inches will be ideal, and
then follow Arnie Coro's advice and paint the paper loudspeaker cone with nailpolish to raise its
low frequency resonance.. The modified small louspeaker will operate as a mechanical audio filter or
sorts that has proven to be very effective and of course will cost you practically nothing.. There
is yet another nice way of optimizing a small louspeaker for CW Morse Code reception , that I will
leave it for an upcoming program... in the meantime try this one and tell me how it worked for
you... send mail to arnie@rhc.cu, or send me an AIR MAIL postcard to Arnie Coro, Radio Havana Cuba,
Havana, Cuba...

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Si amigos, Dxers Unlimited comes to you twice weekly, on Tuesdays and Wednesdays UTC day we have the
mid week edition and on Saturdays and Sundays UTC days we provide you with our weekend edition...
They are two completely different shows, especially written usually on the same day they go on the
air for the first time... But today, there is an exception, as I must participate at a Journalist's
Day celebration on Saturday hosted by the Cuban Ministry of Informatics and Communications.. so I
had to tape the program on Friday... Now here is our HF plus VHF, UHF and Microwaves propagation
update and forecast... Solar activity is from LOW to VERY LOW, and has taken a downward trend that
will very probably prevail for the next seven to 10 days... Sunspot numbers below 20 are expected
during this period, and the microwave solar flux should bottom at figures around 80 to 90 units for
this solar rotation. Dxers Unlimited's fans living along the Gulf of Mexico coastline should be
enjoying excellent tropospheric ducting VHF, UHF and MICROWAVES propagation until at least Monday
evening due to a high pressure stationary weather system. Hope to have joining me for the midweek
edition of Dxers Unlimited next Tuesday and Wednesday UTC days, and please don't forget that your
e-mail messages, postcards and letters do help to make this radio hobby program better for YOU
AMIGOS !!!