Dxers Unlimited
Dxers Unlimited's week end edition for May 3-4 2003

By Arnie Coro

Radio amateur CO2KK




Hi amigos radioaficionados !!! With a BIG sunspot facing the Earth right at this moment you are
listening to the show, solar activity is now once again declining after a peak that sent the daily
sunspot count up to 224 on the last day of April. AND as expected as we move away from the spring
equinox and into the summer season, the daily maximum useable frequencies that those of us that live
in the Northern Hemisphere will see are going to be lower for a given solar flux figure ! I am Arnie
Coro radio amateur CO2KK hour host here in Havana amigos... its nice to share with you about
seventeen minutes of ON THE AIR and ON THE WEB time... Here is item two: Another source of low cost
power supplies for amateur bands transceivers... Yes, you will find them inside dead computers, and
it's not too difficult to make them work again to provide power for equipment requiring 12 volts DC
at currents in the range around 5 amps... More about how to adapt computer power supplies for ham
radio equipment use later in today's weekend edition of your favorite listener oriented radio hobby
program ... Item three: an amazing antenna experiment requiring just a coaxial T connector, a 50 ohm
dummy load, a ground connection and a length of wire no less than 0 point ONE wavelength serves to
demonstrate that under extreme conditions an effective HF link may be established with this unique
emergency antenna system... More about the DUMMY LOAD PLUS WIRE antenna later in today's edition of
Dxers Unlimited, coming to you from Havana... Item four, BIG THANK YOU to all of Radio Havana Cuba's
friends around the world that have sent nice congratulations messages on our 42nd Anniversary On the
Air, that was celebrated May Day 2003 !!! MUCHAS GRACIAS AMIGOS... , and as always at the end of the
show, our exclusive and not copyrighted HF plus 6 meters propagation update and forecast...
Margarita Delgado is my sound engineer and producer , I am Arnie Coro in Havana , back with you
after a brief musical interval...
.....




This is the weekend edition of Dxers Unlimited, coming to you via short wave and also via the
Streaming Audio from www.radiohc.cu.. Here now is item two ... computer power supplies, yes, old
computer power supplies can now be found at hamfests and fleamarkets , as well as in closets ,
attics and garages... The typical computer power supply produces several DC voltages that are pretty
useful for amateur radio equipment use. And two or even three computer supplies may be connected in
series to provide higher voltages and more current.. YES, you heard it right... by carefully moving
the voltage setting of the plus 5 volts section of the units, you can usually reach about 6.5
volts,and that means that two power units modified in that way may be connected in series to obtain
13 volts at currents of 10 amperes and more... Even without changing the voltage setting on two
supply units, you can connect three of them in series and obtain plus thirteen point eight volts ,
as required by many ham radio transceivers... BUT there is certainly one drawback, computer power
supplies used the switched mode operating system instead of the linear mode, and for that reason
they are very powerful noise generators... That can be filtered by the use of ferrite rings inserted
into the power cables, and according to my experience this approach works quite well to power up VHF
FM transceivers for the two meters and 70 centimeters bands. For the HF ham bands some computer
power supplies will generate so much radio frequency noise as to make them unusable for that
application. ANYWAY, if you happen to own a 25, 40 or even 50 watt 2 meter band FM transceiver and
don't want to spend a lot of money for an expensive and bulky linear mode classical power unit, then
connecting two identical computer power supplies in series and tweaking the voltage setting for the
plus 5 volts may be a low cost approach to activate your 2 meter station. ANOTHER use for the old
retired computer's power units is to use them directly to provide 12 volts DC to 2 meter band 5 watt
or less handie talkies... BUT , don't forget to include a good number of ferrite rings in the cable
going from the supply to the FM transceiver. I have used this approach during a hurricane, when
recharging the batteries for the handheld radio while the emergency generator was running. The
computer power supply provided power to the handie talkie to keep the communications going, and that
left the nickel cadmium batteries fully charged for the time when we had to stop the generator for
refueling... SI amigos, safety first, always, and refueling an emergency generator during an
emergency is an operation that you will always want to do with extreme care and not in a hurry at
all...

So, the computer supply came in to fill the gap, and allowed us to keep the communications going
while our crew refueled the generator !

...........

This is Havana, yes, you are tuned to Radio Havana Cuba, now on its 43rd year on the air... May Day
2003 we celebrated our 42nd Birthday amigos, and I do want to thank all of you Dxers Unlimited's
fans around the world that sent such nice congratulation messages to our station... Now item three,
but before it, a short note about short wave listening... another two well known short wave stations
are announcing that they will either go off the air in one case, and that's Radio Denmark, or
reducing their English language broadcasts significantly, and that's HCJB, that is also dropping the
very long time running radio hobby program DX Party Line...You must know that in this two cases,
there is no mentioning of INTERNET audio streaming to replace the short wave programs, both stations
simply are acting from the analysis that there is little audience in one case, and that in the case
of HCJB programming to North America, there is more than enough local program content of the same
nature of what they broadcast to the USA and Canada in English every evening... And after this short
intermediate item , here is page three, item three: It all started as a fun experiment, just to show
some visiting friends that a solid state amateur bands transceiver could be operated into a perfect
one to one standing wave ratio provided by a 50 ohm 100 Watts dummy load, and still be heard all
along the Cuban archipelago on the 40 meter band...

No Arnie, that's not possible... the three of them told me, as I was arranging the DUMMY LOAD, a
coaxial TEE connector , a short length of coaxial cable with two male plugs, and two lengths of PVC
insulated wire, one about 20 feet or 6 meters long and the other about about 4 meters long... By the
way , the length of both wires was totally a random parameter, as they happened to be off cuts from
the recent installation of a new water pump for my home...

I simply connected the 100 Watt transceiver to the DUMMY LOAD, using the TEE connector, then on the
third side of the coaxial TEE I inserted one end of the 6 meter long wire, and just three it out of
the window... The other wire was then connected to the ground butterfly nut of the transceiver, and
was just dropped behind the workbench... Everything was ready for the test... and my friends kept
looking very skeptical... I fired up the rig , and tested the SWR at the 50 Watts power output
level.... sure enough, it was an almost perfect one to one, according to the transceiver's built in
SWR bridge... Then I tuned the VFO to 7110 kiloHertz, our national daytime calling frequency, and
just whistled into the microphone at first, and then said, CO2KK probando, that is CO2KK testing...
As the 7110 kiloHertz frequency is almost constantly monitored by many retired and disabled amateurs
during the local daytime, I was not surprised to hear someone calling me !!! BUT , I must say that
my three friend's faces were pretty funny to say the least... Their amazement continued when the
other station sent its callsign... it was a CO8 in Baracoa, Guantanamo province, that is at the very
extreme Eastern tip of Cuba... and he was giving me a five by seven report... Just to see what
happened , I changed the antenna to my regular cloud warmer two element wire Yagi pointing straight
up into the sky, and the report went up to an S 9 plus 10 dB... quite logical indeed... but going
back to the other antenna, again the ham in Guantanamo province gave us a 5 and 7, totally in the
clear and excellent copy signal... We also tested the DUMMY LOAD PLUS TWO antenna on the 20 meter
band's CW segment, and made several nice QSO's with US and Canadian station, and finally we QSYed to
15 meters and made a real DX contact with an LU station located more than 500 miles South of Buenos
Aires !!! Quite a nice contact for a DUMMY LOAD and two random lengths of wire...

But actually.... was this really a DUMMY LOAD ? And the answer is both YES and NO... the connection
at the TEE coaxial fitting between the transceiver, the dummy load and the wire can certainly
explain how this worked... Part of the power provided by the transceiver was dissipated into the
dummy load, but also a fraction of the power was radiated by the wire... How efficient this antenna
really is ? That's hard to answer, but all I can say is that my station was heard at the extreme
Eastern end of Cuba during local daytime hours with a nice report... and this DUMMY LOAD PLUS WIRE
antenna system may be very well put to work during an emergency situation, when you don't have an
antenna tuner at hand and you must be sure that the rig's output transistors will see a very low
standing wave ratio.... !!!

......

And now , as always at the end of the program , here is our exclusive and not copyrighted, HF plus 6
meters propagation update and forecast... Solar activity will stay at moderate levels, and the solar
flux level took a slight upward shift , indicating the presence of more sunspots. The daytime
maximum useable frequency curve is not at a nice level for the season, but it won't reach the above
40 megaHertz mark as it would had happened during the spring equinoctial period that has just ended.
The Earth's magnetosphere has seen an almost constant impact of the high speed solar wind, and this
situation continued during this week, sending the daily A index to figures above 30 units, enough to
make some astronomy hobby enthusiasts very happy as they saw Aurora Borealis displays at rather low
latitudes... For general short wave listening during the local evening hours the best four bands are
25, 31, 41 and 49 meters, and during your local daylight hours reception will be nice on the 19 ,16
and 13 meter bands... Send your QSL requests, radio hobby related questions and your comments about
this program to arnie@rhc.cu, and VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba. See
you all at the mid week edition of the program next Tuesday and Wednesday UTC days amigos !!!