Dxers Unlimited

Dxers Unlimited's weekend edition for 6-7 March 2004

By Arnie Coro

radio amateur CO2KK

Hi amigos short wave listeners and radioaficionados around the world... nice to have you listening
to our weekend edition of Dxers Unlimited, coming to you from Havana. I am Arnie Coro, radio amateur
CO2KK your friend here in Cuba now ready to provide you with about 17 minutes of on the air and on
the web time devoted to our wonderful and fascinating hobby : RADIO !!! Here is item one:
Equinoctial propagation conditions approaching fast, and already many radio amateur are enjoying
daytime DX on the 10 meter band.. even when solar flux is hovering at rather modest levels.. At the
same time , and due to the low solar activity , the 160 and 80 meter radio amateur bands are
providing excellent DX during local nights amigos !!! So, seems like at this particular moment we
are able to enjoy the best of both worlds, daytime DX at the extreme end of the HF range, and
nightime DX on 160 and 80 meters. My good friend AKI, CO2 Charlie India, told me Saturday morning
during a QSO we had on the local two meter band repeater that he had worked several Japanese
stations on 80 meters CW at sunrise local time here in Havana... And this contacts are possible due
to rather low ionospheric absorption and the enhancement provided by the so called gray line or
terminator line propagation, that is the line that separates DAY from NIGHT on planet Earth,actually
it is not exactly a thin line at all, it's like a band extending both sides of the actual terminator
what makes propagation possible with very low attenuation between locations that

are at sunrise and sunset at the two ends !!!

Item three: I went to Matanzas province on Friday. Matanzas is located to the East of Havana and is
the province where the world famous Varadero Beach at the Hicacos Peninsula receives hundreds of
thousands of tourists from all over the world.

The Varadero Amateur Radio Club is often visited by tourists that are also ham radio operators and
want to know their Cuban colleagues... Matanzas has several 2 meter band repeaters installed , but
two of them are particularly useful when one is traveling by car , as they can be easily reached
using a low power hand held FM transceiver. Those amateur 2 meter band FM repeaters are also
particularly helpful during the hurricane season, as they provide very effective communications
between hand held, mobiles and fixed stations .

I had the opportunity of talking to many Matanzas radio amateurs during my one day trip to their
beautiful province, and as always enjoyed one of the more than 77 ways you and I can have a good
time on the radio... mobile communications !!!

Item four today will be our antenna topics section, and later item five will answer listeners
questions...at the end of the show, as always, our exclusive and not copyrighted HF plus low band
VHF propagation update and forecast will bring the program to its end... Stay tuned, I am Arnie Coro
in Havana, more of Dxers Unlimited's weekend edition follows in a few seconds..

......

Si amigos, this is the weekend edition of Dxers Unlimited coming to you from Havana... NOw here is
our antenna topics section... today I'll tell you about how you can make yourself a compact antenna

that will allow you to operate an amateur radio station or to monitor Dx on the lower frequency ham
bands, the ones that will become more and more significant as solar cycle 23 enters its last three
to four years of activity... My KK-COMP antenna uses a very well engineered combination of inductive
and capacite loading, so its efficiency is certainly above the average compact antenna for the lower
frequencies. Another neat trick that I used when designing these antennas is to make the diameter of
the loading coils as large as practical, so that they will also contribute to radiation and not only
do their job as inductive loading to help shorten the antenna. The experimental version of the
KK-COMP antenna benefitted from a very nice experiment, because I made it for the 10 meter band...
Doing that in order to be able to test the scale model of the antenna easily. The use of actual,
physical scale sized antenna models is in my opinion a reliable method, that makes a nice complement
to the use of antenna modelling software.

A full size 10 meter band dipole antenna requires about 5 meters of wire, 2.5 meters for each leg of
the dipole... That's for those of you still thinking using feet and inches, is about 16 feet overall
length , or 8 feet each side of the center insulator. I decided to reduce the size of the 10 meter
band antenna by 50 percent, in other words to make it just 2.5 meters or about 8 feet long, while
retaining a high efficiency.

How could I tell if the compact version of the antenna was really efficient or not ?

Well, very easily , by using a field intensity meter , and a full size antenna used as a reference.
The procedure used is very simple, you set up the full size antenna up and in the clear, feed it
with 10 Watts of 28.5 megaHertz radio frequency energy and measure the field intensity

at a certain distance, typically no less than 10 wavelengths away from the antenna.. and that's
about a city block away in this case.

Then you replace the reference full size dipole and proceed to test your experimental compact
antenna, measuring the field intensity and writing down the resultant figure.

The a little mathematics will tell you if your compact antenna is doing its job... You can be sure
that the compact antenna will never be as efficient as the full size one, but the fact is that my
design provides an efficiency that is really outstanding when one considers that the compact KK DASH
COMP antenna is half the size of the 10 meter dipole...

After the measurements were finished I proceeded to operate my 10 meter rig using the KK DASH COMP,
and reports coming from radio amateurs in eleven different countries, from Canada to Argentina, and
from Spain to South Africa confirmed that the very small antenna is working very well..

The KK DASH COMP uses a combination of two loading coils and two capacity hats .The loading coils
are located at the center of each wire element, and the capacity hat are placed at the ends. The use
of a combination of inductive and capacitive loading is what makes the antenna very efficient,
because the presence of the circular capacity hats at the ends of the elements makes possible to
reduce the number of turns of each loading coil, and that in turn reduces the losses introduced by
the coils. I must add that the small sized KK-DASH COMP antenna with its two end loading disks is
also very nice looking, as the 30 centimeter diameter disks give it a very distinctive look
indeed...

UPSCALING the design results to the 40 meter band gave me a 7 megaHertz antenna that is the size of
a standard 20 meter band dipole, and that according to my measurements is just -2 dB down from the
full size radiator... And that minus 2 dB difference is easily compensated by increasing the
transmitter power output. For the many radio amateurs around the world that suffer from lack of real
estate to be able to install full size lower bands antennas, the KK DASH COMP is a practical , low
cost , solution that you can homebrew during a single weekend... If you found this information
useful and want to know more about my KK DASH COMP compact inductive and capacitive loaded antenna,
just send me an e-mail to arnie@rhc.cu, or an AIR MAIL postcard to Arnie Coro, Radio Havana
Cuba,Havana, Cuba.

.....

Soon to celebrate its 43rd year on the air, and now also available on the world wide web, this is
Radio Havana Cuba, the name of the show is Dxers Unlimited, and this is our modest twice weekly
contribution to the development of the radio hobby amigos !!! Here is now ASK ARNIE, THE most
popular section of the program ,. according to what your letters and e-mail messages tell me evey
week.. Question one today: Came from several listeners located in Australia, New Zealand, Japan, the
USA and Nigeria... they all want to me to provide an answer to their question .

They want to know if it will be worthwhile to buy a radio receiver that is not operating , in other
words a broken down radio... Each of those that wrote quotes a particular model of radio, and as
expected, the price asked for the radios was quite reasonable... Well amigos, first things first...

When buying a radio receiver that is not operating to its full factory parameters you are certainly
running a risk...but if the price is low enough I can assure you that it will be a win-win
deal,because , and now listen carefully to this, in the extreme case that the receiver may not be
repaired, you will end up with lots of useful electronic components that can be effectively recycled
and used for many radio hobby related experiments.

The other side of the coin will show you that many radio receivers , especially those built before
1970, can be rathe easily repaired and restored back to like new or even better than when new
conditions..

For example, so called boat anchors, or old vacuum tube communications receivers,often come back to
life by just changing a few electrolytic capacitors, replacing paper bypass capacitors and checking
the vacuum tubes .

First generation solid state communications receivers are also a lot easier to repair than the most
modern microprocessor controlled radios. My advise is that you stay away from the more modern
receivers , because they are very difficult to repair, and in many cases they can not be put back to
work because of the way they were built !!!

Follow your friend's Arnie Coro advice and look around at hamfests and flea markets, garage sales or
even ask friends if they happen to have an old radio somewhere in the attic or garage... You will be
pleasently surprised when that old radio comes back to life giving you many hours of listening
enjoyment... AND, if you don't have too much space to keep them, then the repaired radio can be
passed along to a newcomer to the hobby at cost, or perhaps for free !!!

....

QSL,QSL on the air to the many Radio Havana Cuba listeners that have sent so many nice signal
reports of our new transmitter tests... Our Chief Engineer at the Bauta transmitting station is very
happy with the reports I have forwarded to him and his crew... And they keep on working now
installing still more transmitters and new antennas to give our station much better coverage and
transmission quality.

For those that kept on faithfully listening to Radio Havana Cuba when we were on the air with very
old, obsolete equipment, our thanks, and our hope that you all will enjoy our programming much more
now that already four of our new transmitters are on the air on a regular basis.
And now as always at the end of the show, our exclusive and not copyrighted HF propagation update
and forecast.. the daily optical sunspot count is now between 50 and 55, and the effective sunspot
number or SSN is now near 60 units. The planetary A index on Friday was 8 , and it seems like it
will be moving down , while the daily

microwave solar flux will be moving slowly up to values around 120 units, that are ideal for Dx
conditions to show up during local daylight hours on the 10, 12 and 15 meters band now that we are
approaching the spring equinox, here in the northern hemisphere. So,its time to be active on the
radio amigos, you can always return to the workshop and play with your equipment when HF propagation
conditions take a turn for the worse later in the year !!!

Don't forget to send your comments about today's program, radio hobby related questions and QSL
requests to arnie@rhc.cu of VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba... hope to
have listening to our mid week edition of Dxers Unlimited next Tuesday and Wednesday UTC days...