Dxers Unlimited

Dxers Unlimited's weekend edition for 5-6 August 2006

By Arnie Coro

radio amateur CO2KK

Hi amigos radioaficionados ! Welcome to the weekend edition of your
favorite listener oriented radio hobby program coming to you from
Havana... I am Arnie Coro, radio amateur CO2KK and here is item one...
Spent about an hour and a half Friday evening enjoying some nice 20
meters CW sub band contacts... As usual during the summer months the
band was in much better shape during the local evening than during the
day time, something that happens because the ionosphere heats up due to
the intense summer solar radiation that it receives, expanding in such a
way that the free electron concentration during the daylight hours if
very low... In other words, propagation is poor until the sun sets and
the ionosphere begins to contract, increasing the number of free
electrons per cubic centimeter, and sending the maximum useable
frequency curve UP, even after sunset, once again , a typical summer
season phenomena.

My CW sending around 14.060 kiloHertz , the spot where QRP or low power
amateur radio operators around the world

gather to work other QRP enthusiasts, attracted the attention at first
of a Canadian station located in Ontario, and later I was able to work
several US stations while remaining on the same frequency. The band
finally died around midnight local time, as I was carefully watching
what was happening with Tropical Storm Chris, that fortunately
dissipated during the early hours of Saturday, becoming just another
broad area of low pressure that will bring some rain to eastern and
central Cuba.

Item two: Checking the electrical installation at my home on Friday, I
found two of the wall sockets that needed tightening of the screws that
hold the wires carrying the power.I discovered the problem when removing
a power plug and finding that it was hot to touch, an indication of a
poor contact... When was the last time that you had an electrician check
your home's electrical installation ? I am asking this question ,
because you should check your house wiring and connections at least once
every two years or so, and at any signs of overheating or tripping of
circuit breakers, don't try to deal with the situation yourself, ask

a professional electrician to do the job... And YES, this topic is
certainly connected to the radio hobby, because defective home
electrical systems generate a lot of unwanted radio frequency noise that
severely disrupts radio reception !!!

Stay tuned for more radio hobby related information amigos, and don't
forget to send me your comments about the program, signal reports and
radio hobby related questions to arnie@rhc.cu or Via Air Mail to Arnie
Coro, Radio Havana Cuba, Havana , Cuba...

.....

Si amigos, yes my friends, your radio is tuned to one of Radio Havana
Cuba's short wave frequencies, and our English language program is also
presented as streaming audio from our website during the 05 to 07 UTC
segment. Now here is item three of today's program...Another short stop
at Arnie's workshop, where the old Kenwood PS-30 power supply that was
totally rebuilt passed the whole set of tests with flying colors... Each
of the more than seven hours invested in doing the job was really worth
the time spent, because the power supply capable of providing 15 amperes
continuous duty or 20 amperes for brief periods at a nominal 13.8 volts
, is now actually working better than when it came out of the factory

in Japan... This is something perfectly possible when you upgrade the
electronic design of a particular piece of equipment , introducing state
of the art technology. The original very well built with first quality
components Kenwood PS30 power supply used a discrete components voltage
regulator circuit to keep the output voltage within

certain limits despite the variations in load. The two very much
overrated series pass transistors used by the Japanese engineers in the
original design are rated at 25 amperes each, although , as you have
just heard the supply is capable of providing brief periods of 20
amperes peak current...

The series pass transistors are fed from a circuit board that originally
contained about 25 discrete components... including a voltage reference
or Zener diode and two transistors. What I did was to replace the whole
circuit board with one of identical dimensions, but that replaces the
individual electronic components with a high performance integrated
circuit voltage regulator, an up to date technology medium power
transistors and a few bypass capacitors.

I used several high wattage resistors to load the power supply to
current outputs of 1, 2, 4, 8, 12, 16 and 20 amperes, setting the
voltage output to the nominal 13.8 volts with a high quality
potentiometer, a critical component in any voltage regulator circuit...

Then , using a digital high precision multimeter, and a well calibrated
analog current meter, I took measurements of the voltage output at the
1, 2, 4, 8, 12, 16 and 20 amperes , something that made me a very happy
electronics experimenter, as the voltage output stayed with just a few
millivolts, or thousands of a volt, while the current output changed in
a 20 to 1 ratio, a tough test for any voltage regulator circuit by all
standards.

Now the refurbished Kenwood PS30 power supply with its brand new voltage
regulator board, is sitting right next to the old Ten Tech 540 HF
amateur bands transceiver that I use as a standby rig on the 40 meters
band every time a tropical storm or hurricane is approaching the area...

By the way, as my good friend Jose Amador, a professor at Cuba's most
well known technical university likes to say, never throw away an old
piece of equipment that looks cosmetically in a good shape, because many
times it can

be totally rebuilt, its circuits upgraded to present state of the art,
so that you can both save a lot of money and at the same time enjoy
reviving the equipment, just as I did with my ailing and aging Kenwood
PS 30 Power Supply, that now is waiting for a trip to a friend's home,
where it would get a new paint job to complete the total upgrade !!

....

QSL, QSL on the air, yes QSL on the air to the many listeners that have
reported our new 11760 kiloHertz antenna system... Thanks amigos, and
yes we are very happy with the results of this rather simple and rugged
antenna system that provides almost perfect omnidirectional coverage of
the first and second skip zones on the 25 meters band...

We are now running a similar antenna on 5965 kiloHertz with our nightly
Spanish language program from starting

at 00 UTC and until 05 UTC...

Now here is item five: Antenna topics section of Dxers Unlimited back on
the air now... More tests of the Moxon rectangle antenna for the 2
meters band left me amazed with the performance of such an easy to build
antenna system that when built with reasonable care doesn't even require
any adjustments . The two meters band Moxon built using number 12 solid
copper wire is a little tooo flexible, so

the next one I am going to build for a friend during this weekend will
be made using number 8 solid copper wire.

It will weight more, but it is certainly going to be much more rigid...
The Moxon's I am building for the 2 meters ham band use a one inch or 25
millimeters white PVC water pipe as a support and they behave very well
even under severe weather conditions, IF,and here is the IF, IF the
wire used for building the antenna is at least a number 10, or better
yet the larger diameter number 8 rigid solid copper wire.

Yes, the Moxons can be installed in stacked pairs , and each pair will
provide about 6 dB gain over a dipole in a horizontal sector of about
120 degrees, making this antenna system ideal for FM repeaters that
share their frequency pair with others that are close by...

As a matter of fact, I am now gathering all the necessary parts to build
4 Moxon rectangle antennas, that will be

connected as two stacked pairs, so that my 2 meters band amateur radio
station will have an improved coverage towards the most popular
repeaters that are located unfortunately at right angles to each other,
something that requires using one of the following combinations... one:
high power and an omnidirectional antenna, two: a high gain Yagi ,
vertically polarized of course, and installed with a remote controlled
rotor, so that you can aim the antenna to each of the distant repeaters,
and the third low cost and more logical solution, that will both be
simpler and energy saving, is to build and install two sets of Moxon
rectangle pairs, and place them on your mast or tower aiming in the
general direction of the repeaters, something that with the broad
horizontal pattern of the Moxon is easily achieved.

I have kept in one of my hard drives a very small software program that
calculates the Moxon antennas for a wide range of frequencies and with
different antenna element diameters... You can send for it via e-mail.
Send an e-mail message to arnie@rhc.cu, and include in the subject line
or the body of the message Moxon Antenna Software...

Of course that if you want to know more about this extremely interesting
antenna, you can just type the two

words Moxon plus Antenna to any of the popular Internet search engines,
and then start by visiting http://www.cebik.com, the website of W4RNL,
Dr. L.B. Cebik PhD.D. an antenna

expert that is capable of making antenna theory and practice understood
by almost everyone in the world ...

And now amigos,as always at the end of the program... here is our
exclusive and not copyrighted HF plus low band VHF propagation update
and forecast, direct and from the source... Sunspot number is ZERO,
yes,you heard it right

ZERO, a totally blank solar disk ... Solar flux is at baseline level of
70 units and the A index the geomagnetic disturbance indicator was also
at very low levels, a confirmation that we are going trough the extended
solar minimum of cycle 23, expected to last until at least the end of
the year 2007. The probabilities of short skip sporadic E layer openings
are moving down, something typical of the month of August, and once
again, as I said earlier in the program, the best time for hunting for
DX stations is starting just after local sunset... Hope to have you
listening to the mid week edition of Dxers Unlimited next Tuesday and
Wednesday UTC days, and don't forget to set aside a little time and send
me your valuable opinions about my program, your signal reports and any
radio hobby related question that you want me to try to answer amigos.
Send e-mail messages to arnie@rhc.cu, and VIA AIR MAIL,send your
postcards and letters to Arnie Coro, Radio Havana Cuba, Havana, Cuba