Re: [HCDX] Dxers Unlimited´s mid week edition for 19-20 February 2008

["Prof. Arnaldo Coro Antich" <inforhc@xxxxxxx>]

RADIO HAVANA CUBA

DXERS UNLIMITED

DXERS UNLIMITED´S MIDWEEK EDITION FOR 19-20 Feb 2008

BY ARNIE CORO

RADIO AMATEUR CO2KK

Hi amigos radioaficionados… you are, as always, welcome to the mid week 
edition of this, your favorite radio hobby program, Dxers Unlimited, the 
one and only covering practically all aspects of our wonderful hobby, 
from what can best be described as classic short wave listening, to 
backyard radio astronomy, from homebrewing your own radios to 
participating in one of the really big amateur radio contests with your 
own station… Si amigos, I am Arnie Coro, radio amateur CO2KK and here is 
our first item of today´s program. ARRL CW contest that took place 
during the weekend provided many radio amateurs around the world with a 
very nice opportunity of working some really rare DX spots, like Ducie 
Island, VP6DX, one of the best run DX expeditions that I have heard in a 
long time…. I wanted to participate, but had a backlog of ¨honey do 
this, and honey do that¨¨ so it wasn´t possible to spend some time 
sitting at the operating position of CO2KK my ham radio station… As a 
very good friend of mine, Jose Angel Amador CO2JA likes to say, if you 
really want to take part in an amateur radio contest, the best option is 
to do it away from home… By the way, Jose Angel was the pioneer of 
amateur satellite communications here in Cuba… and he is now a senior 
professor ot telecommunications engineering at our main technical 
university here in Havana, where he has helped several students to 
obtain their ham radio licenses…

Item two: Digital communications continue to make possible nice two way 
ham radio contacts using low power and simple antennas even at the very 
low ebb of the solar cycle…

Amateur digital communications have also opened up the hobby to hard of 
hearing or deaf persons, thatare now able to enjoy ham radio by going on 
the air using modes like PSK31 and MFSK16 that provide full on screen 
text and graphics plus complete control of the station without the 
operator having to listen to any sound… Item three: Had a bad computer 
crash at my home QTH…so for the past several days I have had to work 
with a borrowed machine, and so far the e-mail address book is still 
inside the broken computer, that just refuses to produce a video output 
despite all my efforts, including installing a plug in video card 
without any success…

SO my apologies to Dxers Unlimited´s listeners that had written e-mail 
messages that I could not answer before the computer broke down… I am 
planning to disassemble the broken computer and extract the hard drive 
to so that the e-mail address book can be recovered…

More radio hobby related information coming up in a few seconds , when 
the mid week edition of Dxers Unlimited will continue here in a few 
seconds… I am Arnie Coro, radio amateur CO2KK in Havana… stay tuned…

…………………

Si amigos , you are listening to RADIO HAVANA CUBA, the name of the show 
is Dxers Unlimited, and now here is item four of our program.. It is our 
popular Technical Topics section that today will be dealing with yet 
another version of a short dipole antenna for the 40 meters band… This 
was one was created by a British radio amateur, GM4JMU and can be easily 
homebrewed using readily available materials.

The overall length of this shortened 40 meter dipole is practically the 
same as a 20 meters band half wave dipole,and it has proven to be pretty 
effective in actual operation. A Cuban radio amateur friend built this 
GM4JMU antenna and simply connected it in parallel with his existing 
half wave 20 meter band dipole, so he very easily was able to achieve 
dual band operation in a very limited space.

The GM4JMU dipole for 40 meters uses two very easy to build loading 
coils, that consist of 40 turns of PVC insulated number 16 wire, of the 
type used for household installations, that are wound on a plastic form 
of 40 millimeters diameter.

The actual length of the wire for makin each coil is ten meters and 25 
centimeters… and the coils are located at 2.6 meters from the center 
insulator. The length of wire after the coils is used to actually tune 
the antenna to the part of 40 meters where you want to operate more 
often. You start with about three meters of wire after each coil, 
install the antenna at its operating height, and run a test for standing 
wave ratio between 7000 and 7200 kiloHertz. In my case, the antenna that 
I built was resonated to obtain a minimum standing wave ratio on 7050 
kiloHertz, something that provided an excellent compromise to work both 
CW DX and the Digital Modes , with the antenna showing a rather nice and 
low standing wave ratio between 7000 and 7100 kiloHertz. As recommended 
by GM4JMU, I used a one to one balun to feed the antenna with 50 ohms 
coaxial cable. 40 meters is an excellent amateur band for year round 
operation even during the worst periods of the solar cycle, and for 
those of you without enough space to install a full size 40 meters band 
dipole, the GM4JMU design is an excellent compromise.

When on a field trip some time ago, I was able to take with me both a 
short GM4JMU dipole and a fullsize antenna for the 40 meters band. I ran 
comparative tests and not surprisingly, the difference between the two 
antennas was barely noticeable. According to antenna modeling software 
the GM4JMU and similar half size shortened half wave dipoles should be 
between minus 3 and minus 6 dB below a full size antenna, depending on 
how high the short antenna is installed above average terrain. So, even 
in the worst possible scenario this short antennas are one S unit below 
their full size counterpart, with the advantage that they may , in many 
cases, make the difference between been able to operate on 40 meters or 
not…Now, don´t think that this antenna is as easy to install and get 
running as a full size half wave dipole… you will need to be patient and 
tune the antenna to resonate to the part of the 40 meters band you want 
to operate, but once this is done, you won´t need to do any further 
adjustments if you don´t move the antenna from the place where you 
installed and adjusted it…

……………….


If you have a particularly difficult place to install a short wave 
receiving or transmitting antenna, just send me the description of the 
location, and maybe a photo or diagram, so that I can recommend options 
that may allow you to enjoy the use of a better antenna system… send 
mail to arnie at rhc dot cu or VIA AIR MAIL send a letter to Arnie Coro, 
Radio Havana Cuba, Havana, Cuba…

Si amigos, yes my friends, space restrictions, condominium and owners 
associations antenna banning can be circumvented with the usual radio 
hobby people ingenuity… Do keep in mind that even a very small outdoor 
antenna will usually be a much better performer than one that is located 
indoors amigos !!!

……..

QSL, QSL on the air, QSL on the air to the many Dxers Unlimited 
listeners around the world that have sent me their thank you notes for 
publishing the scripts of the show by means of several Internet radio 
hobby mailing lists.. Among the latest ones that are publishing the 
scripts of the program for the benefit of their readers are the ANTENNEX 
Webzine antenna discussion list, and the also popular swl list that is 
distributed via the qsl.net site…If you know of any other e-mail radio 
hobby distribution list that is also reproducing Dxers Unlimited script 
please let me know about it… send mail to arnie at rhc dot cu… again 
arnie at rhc dot cu.

And now here is our next item…it´s about the testing of recycled 
electronic components salvaged from broken down or discarded equipment. 
My storage bins are presently full of recycled electronic components.. 
and finally I was able to start a long time project aiming at testing 
each recycled part in storage and from now on testing newly salvaged 
parts before putting them in storage…The latest piece of equipment that 
became available for dis-assembly and total recycling of its components 
is a SONY Betamax VCR machine, that will probably take a few more days 
to take if apart completely. It is a treasure chest of both electronic 
components and mechanical parts, including a lot of very useable hardware…

A nice power transformer, large electrolytic capacitors and several 
optocouplers that are very useful when building digital radio interface 
boxes required to operate between a computer running a digital modes 
communications program and a transceiver. The optocouplers are very 
effective in isolating the computer from the radio, providing protection 
to the machine´s serial or USB ports…

VCR machines will become in the not too distant future yet another nice 
source for recycling electronic components , as DVD´s and hard drives 
recorders become more and more popular among TV viewers… So keep a close 
watch around for those VCR machines that are going to be phased out by 
the new recording and video reproduction technologies amigos !!!

Other sources of recycling are computer monitors, especially the older 
ones, that will provide your parts bins with a lot of high quality 
components including a large number of discrete transistors and first 
generation integrated circuits that can be easily desoldered from the 
circuit boards…

…………………

And now amigos, as always when I am here in Havana, get ready to copy 
Arnie Coro´s exclusive and not copyrighted propagation update and 
forecast… Solar activity is expected to continue at very low levels for 
the next month or so… Scientists are anxiously awaiting for yet another 
sunspot that can be attributed to the new solar cycle, something that 
will really confirm that the new cycle has really started… Solar flux 
should remain between 70 and 75 units for the next three to five days, 
and this will mean that the maximum daytime useable frequency for the 
best propagation paths would briefly exceed the 21 to 23 megaHertz 
range, with the frequency of optimum traffic curve hovering around 
eighteen megahertz during your local daytime hours, something that will 
explain the good reception achieved on the 16 meters international 
shortwave broadcast band…

For amateur radio operators that come in from work after five or six PM 
local time the 20 meters band will be closing very shortly after you 
arrive at your home QTH, leaving those of you that are good CW operators 
with the nice option of operating on the 30 meters or ten point one 
megahertz amateur band… The rest of the evening your two choices will be 
40 meters and 80 meters, with 40 meters much more attractive for Dxing 
with low powers and not too efficient antennas… DO keep in mind that 
digital modes, especially the popular PSK31 are much more effective to 
communicate when poor propagation conditions due to very low solar 
activity prevail, something that is exactly what is happening now… See 
you all the the weekend edition of the program next Saturday and Sunday 
UTC days amigos…


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