[BARC-List] DXers Unlimited

[Dan Malloy]

Radio Havana Cuba 
Dxers Unlimited 
Dxers Unlimited's mid week edition for 14-15 February 2006 

By Arnie Coro 
Radio amateur CO2KK 

Hi amigos radioaficionados around the world and hovering around the Earth in
space. Here is the mid week edition of your favorite radio hobby program,
coming to you from Havana. I am Arnie Coro, radio amateur CO2KK and as
always its my pleasure to share with you all about 17 to 18 minutes of on
the air and on the live web audio time, plus the opportunity for many of you
to read the scripts of the show too at www.radiohc.cu English website. 
Here is now item one: Solar activity continues at rock bottom levels, with
more ZERO sunspot days in sight, although the far side of the Sun seems to
be witnessing the development of at least one BIG sunspot. The very low
solar flux impacting upon the Earth's ionosphere has led to extremely nice
low frequency propagation conditions, so good in fact, that I have received
here in Havana some AM medium wave broadcast band stations located more than
one thousand and even one thousand three hundred miles away in full daylight
more than an hour and half after local sunrise.When asked by a local radio
amateur who also has heard those DX AM broadcast band stations during the
past few days, I explained to him that this phenomena was caused by a very
low ionospheric absorption of low frequency radio waves taking place at the
D layer . The almost non existent D layer during the very early local
morning hours doesn't block the path of the low frequency waves coming from
areas located to the North and South West , where the Sun has not gone above
the horizon yet. 
More Long Wave and Medium Wave AM Broadcast Band DX, as well as very nice
160 and 80 meters amateur bands propagation is expected to continue until
the last weeks of the upcoming SPRING EQUINOCTIAL period, when SUMMER static
discharges caused by thunderstorms make low frequency reception very
difficult due to the worsening signal to noise ratio. 
Item three:  ASK ARNIE today will be dealing with two listeners questions.
one came in like this : Arnie should I include a coil of the coaxial cable
down lead at the base of my radio tower or not.. And the other one read:
Arnie , can I stack 2 or more MOXON rectangle antennas to build up more gain
for our radio club's two meter band repeater in a direction where there is
much more ham radio activity. 
I'll be answering both questions in a short while, when Dxers Unlimited's
mid week edition continues after a short break. 
I am Arnie Coro in Havana. 

. 
Si amigos, yes my friends, I will once again be answering your radio hobby
related questions here at ASK ARNIE, la numero uno, the most popular section
of Dxers Unlimited, according to your e-mail messages, letters, postcards ,
FAX letters and when I have the unique opportunity of talking on the radio
with many of you . Today's first question: Amigo 
Alex from Vancouver , Canada, tells me he has read that it is always a good
idea to add a coil made of the same coaxial cable down lead to be placed at
the base of the tower or mast supporting the antennas. ANSWER: sure amigo,
but there are two things that you must watch. number one you don't one a lot
of cable to be coiled at the base of the tower or mast if you are using your
equipment at frequencies above 50 megaHertz. and number two: the coil
diameter for it to be really effective for two purposes must be around  20
centimeters or 10 inches. This coaxial cable choke coil will keep radio
frequency currents flowing on the outside of the cable's shield from keep on
traveling into your radio amateur station, and at the same time will help to
reduce the impact of a lightning bolt , in case your tower or mast is hit
from a secondary branch of lightning. Of course that nothing will save your
installation from a direct hit by lightning, but it is a very good idea to
protect yourself from secondary bolts that also cause damage. At CO2KK, my
amateur radio station, the antenna towers are grounded, and the coaxial
cables coming away from them are also grounded right at the tower, and
provided with 10 turn coaxial cable choke coils. It's something that won't
cost a lot of money and give you peace of mind , so go ahead and do it amigo
Alex. 
There is nothing to loose and much to be gained, but again, if you are
operating on frequencies above 50 megaHertz reduce the size of the coils
accordingly. 

Question two: Amigo Frank ,from Georgia, USA, is asking about the
possibility of using a stack of MOXON rectangle antennas for his radio
club's repeater. Sure amigo Frank , you can homebrew the MOXON rectangle
antennas using copper pipe , 90 degree copper elbows, TEFLON insulators and
stainless steel hardware at very low cost, as compared with factory built
antennas. 
A well built pair of MOXON rectangles, made from12.7 millimeters copper pipe
, and spaced at a separation between the center of the two antennas of one
wavelength, will provide about 6 dB gain over a dipole in the most favored
direction, to which you must add that the extremely high front to back ratio
of these antennas will help to produce a deep NULL in the direction of
another 2 meters band repeater using the same pair of frequencies as yours. 
The phasing harness between the two antennas must be made using high quality
75 ohms coaxial cable sections that are cut to an exact number of odd
quarter wavelengths, taking into consideration the coaxial cable's velocity
factor. 
The two 75 ohm sections are connected together, and from that common point ,
you continue down to the shack with 
50 ohms coaxial cable. 
The MOXON RECTANGLE ANTENNAS are an excellent choice for mountain top
repeaters and high rise building installations, because they are very rugged
from a mechanical point of view, with a low wind resistance factor and also
they can be installed very easily with a very simple type of mast or tower
to antenna mount. 
Seventy centimeter band amateur repeaters can also benefit from the use of
MOXON RECTANGLE stacked antennas, and on that band, they are much smaller,
so you can install even a sophisticated SIXTEEN ANTENNAS almost omni
directional array at a relatively low cost. 
AH, and before I forget, do remember that I have here at hand, and ready to
be sent, a small WINDOWS software program that calculates the MOXON
RECTANGLE antenna dimensions for different frequencies and using different
diameter elements. The MOXON CALCULATOR can be obtained as FREEWARE, by
sending your request to the following e-mail address: ready to copy ??? OK, 

arnie at rhc.cu,  again, very easy to remember arnie at rhc.cu. 
The MOXON CALCULATOR program is very small, and works on WIN98, WIN2000,
WIN2000 PRO and WIN XP, and lends itself for experimenting, as you can watch
how the dimensions of the antenna change while you tell the program 
to calculate the antenna using different diameter elements. 
.. 

This is Dxers Unlimited's mid week edition, and yes we do QSL, we do verify
reception reports and send out QSL cards to radio listeners around the world
that send us signal reports and comments of our programs to arnie at rhc.cu, or
VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana , Cuba.remember to
include the date, time, short wave frequency, signal report and short
description and comments 
about what you have heard here.Now here is item five: Seems like there are
many hyperlinks to Dxers Unlimited's published WebPages , and people from
all around the world keep sending me questions about many projects presented
here . One of those recent requests made be remember that THIS, is THE TIME
of the year to homebrew equipment for people that live in cold and very cold
climates regions, because you have to stay inside, at home due to the
extremely low temperatures outside. That's why , after learning about the
very cold weather in North America and 
Western Europe during the 2005 to 2006 WINTER SEASON, I want to remind you
about a very nice piece of equipment featured many years ago here in Dxers
Unlimited, that can be easily built and that will improve the performance of
even expensive radio receivers and transceivers. 
YES, I am talking about Arnie Coro's CO2KK Dxers Unlimited's KK-9 DASH TWO,
a box that contains an antenna input over voltage protection circuit, a
sophisticated radio frequency input attenuator, a tunable band pass dual
tuned input circuit, PLUS two options for adding an additional variable gain
radio frequency amplifier stage. 
The box is installed between the antenna and the radio, and it has proven to
be an excellent external accessory for many shortwave radios, especially the
low and medium cost receivers, but let me add that tests that I have done
with expensive, sophisticated short wave receivers have demonstrated that
inserting the KK-9 DASH TWO box between the antenna and the radio improves
reception and provides a safety path to ground of static electricity
accumulating on large sized external antennas, something that has destroyed
the radio frequency amplifier input stage of many solid state radios that
were connected directly to the antenna without any protection device 
The KK-9 DASH TWO is also a very effective antenna tuner and input filter,
to which you may add two more modules, if they are required at your
particular location.a low pass and a high pass input filters. If your
receiving station is located near an AM Broadcast Band station's transmitter
site, then you will certainly benefit by including the filter that will
produce a very significant attenuation of signals below 3.4 megaHertz .Sure,
don't worry, I will explain now why the KK-9 DASH TWO additional module has
that cut off frequency, and the reason is that the end of the AM medium wave
broadcast band is now at 1700 kiloHertz, so the still powerful second
harmonic of a local station operating at the top end of the EXPANDED BAND ,
that is from 1650 to 1700 kiloHertz will be also attenuated by no less than
30 decibels by the additional filter. 
At some locations the problem is at the high side , above the HF short wave
frequencies, and there you will want a filter that will produce a sharp
attenuation above 40 megaHertz. 
In an upcoming edition of Dxers Unlimited, I will be telling you more about
the KK -9 DASH TWO box that is a nice project to homebrew during what's left
of the cold winter months of the Northern Hemisphere, where 99 percent of
Dxers Unlimited's audience lives !!! 
And now, time is up, so here is our exclusive and not copyrighted HF plus
low band VHF propagation update and forecast. Solar activity will continue
at very low levels for at least one more week, if no new sunspot regions
appear on the Sun's surface that we can see from Earth. Solar flux at
microwave frequencies around 10.7 centimeters wavelength will stay below 80
units , so expect very low daytime maximum useable frequencies, with best
propagation conditions for DX on the HF bands happening during two well
defined peak periods, one about two hours before your local noon with beam
headings to the North and North East, and a second one near local sunset
with beam headings straight South and to your West and North West. 
Hope to have you all listening to the weekend edition of Dxers Unlimited coming to you next Saturday and Sunday UTC days. and please do set aside a little time to send me your signal reports and comments about today's program to arnie at rhc.cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba