Dxers Unlimited
Dxers Unlimited's mid week edition for 29 -30 April 2003

By Arnie Coro

Radio amateur CO2KK

Hi amigos radioaficionados ! You are now listening to the mid week edition of your favorite radio
hobby program. I am Arnie Coro, radio amateur CO2KK and as always its my pleasure to share with you
about seventeen minutes of on the air or on the web time talking about our wonderful hobby: RADIO.

And here is item one: another upsurge in solar activity that is now keeping solar researchers pretty
active. They are particularly interested in the behavior of the downward phase of the solar cycle
and how this may impact the upcoming cycle 24's startup. Item two: There are some nice materials
that can be used to make some very useful and interesting antennas... and those materials are not
usually related to antenna building projects. For example, a copper foil tape with an adhesive
backing, used by another nice hobby, making glass

Artwork, happens to be perfect for making some really practical antennas... More about copper foil
tape antennas in today's edition of Dxers Unlimited. Item three: Modifying old receivers that do not
qualify as collector items or candidates for museum collections, is a lot of fun, and it is really
amazing what can be achieved by retrofitting new technology to some of those radios... In our
technical topics section here today, I will be including some of the easy to do modifications to old
receivers, both vacuum tube and first generation solid state, in order to improve their performance.
Item four: YOU HAVE QUESTIONS , the now number two most popular section of Dxers Unlimited will be
answering a question sent in by a number of listeners regarding computer generated noise and how to
deal with that really dreadful problem for radio listeners. AND , as always at the end of the show,
Arnie Coro's Dxers Unlimited's not copyrighted and in the public domain, HF plus 50 megaHertz
propagation update and forecast. Stay tuned right on this frequency, or keep your connection to
www.radiohc.cu , as Dxers Unlimited continues in just a few seconds. Margarita Delgado is my sound
engineer and producer. I am Arnie Coro in Havana

......

Si amigos, you are listening to the mid week edition of your favorite listener oriented radio hobby
program... Here is now item two, copper foil tape antennas !!! You will find copper foil tape with a
very nice adhesive backing at specialized hobby shops that cater for glass artists... And we radio
enthusiasts should be thankful of those artists , because they require several different widths of
copper foil tape for their glass artwork. The copper foil tape is very shinny and nice looking, and
its conductivity is second only to silver ! The fact that the copper foil tape has some kind of very
powerful glue on one side of it, makes possible the construction of some very nice antennas that
work very well. Let's see two examples: Example number one, the copper foil tape dipole for the two
meter band... I have one installed right on my home office's picture window.. It is not right at the
center of the window, but carefully pasted to one side of the large glass panel, where a curtain
keeps the antenna out of sight. The copper foil tape dipole here is made of a tape that is about 25
millimeters or one inch width, and the coaxial cable that is attached to the center of the dipole is
the very thin RG174, coming out straight at a 90 degree angle from the dipole. The copper foil tape
antenna has a low standing wave ratio over all of the two most used megaHertz of the two meter band
, and this antenna I can keep connected even in the middle of a thunderstorm, something that can not
be done with the external high gain antennas. It's a dipole, so the gain relative to a dipole is
ZERO DECIBELS of course... but it does provide a much better signal into the three metropolitan area
repeaters than the rubber ducky helical antenna of the handie talkie.

When the copper foil tape dipole was built, I started with a somewhat longer length of each branch
of dipole than what was required by the formula, and then very carefully started to cut equal
lengths of tape on each leg of the dipole , until a one to one standing wave ratio was achieved at
145. 2 megaHertz, the center of the part of the band most used locally here in Havana. The very thin
RG174 cable run must be very short, due to the high losses on two meters, so I only use it to go
from the picture window frame to the antenna feedpoint. Then the RG174 is connected to a length of
RG8X, that goes to the two meter band radio located right next to my desk.

Now the second copper foil tape antenna: Its a beautifully looking spiral wound vertical ... The
copper foil tape in this case is about 12 millimeters or one half inch diameter, and it is spiral
wound on a three meters or almost ten feet long CPVC plastic water pipe. The copper foil tape is
wound with a pitch that keeps a spacing equal to the width of the tape for a very nice looking
antenna... No attempt was made to actually tune the antenna to a specific amateur band... what I
have done is to simply use this vertical spiral wound element as part of an antenna system that can
be tuned very efficiently from about 10 megaHertz all the way up to the high end of the ten meters
amateur band, that is 29.7 megaHertz. A set of eight elevated ground radials complete the system
that is tuned with a PI network tuner located right at the base of the spiral wound vertical. In
order to protect the copper foil tape spiral wound vertical, I gave it several coatings of a
transparent acrylic paint. The connection from the bottom of the antenna to the tuner is via a
length of coaxial cable shield that is flattened out and soldered to the copper foil at one end and
to a connector at the other end to interface with the PI Network tuner. This antenna was not
intended for fast bandswitching, it was built in order to test the bandwidth of the copper foil tape
spiral wound on a two inch or about 50 millimeters diameter CPVC water pipe, and results obtained
show that it provides excellent matching and low angle radiation on the 30, 20, 17, 15, 12 and 10
meter bands when manually tuned to frequency at the base of the system. The radials were cut for the
30 meter band and no attempt was made to tune them to each operating band. The vertical 3 meter
length section of CPVC water pipe capable of supporting up to 10 atmospheres of pressure or some 150
pounds per square inch, has a rather thick wall, and is supported on a length of 4 by 4 inch or 100
by 100 millimeters wood mast that keeps the base of the antenna at about 1 meter or three feet from
the ground level. Si amigos, yes my friends , oui mes amis, copper foil tape antennas are fun to
build, look nice and you can make them pretty fast, as the copper foil tape is self adhesive to any
clean surface.. And last but not least, these are really low cost antennas by all standards !!! If
you want to know more about copper foil tape antennas, just drop me an e-mail to arnie@rhc.cu ,
again, here is my e-mail address, arnie@rhc.cu...

.......




Item three.... old vacuum tubes and first generation solid state radios can be easily upgraded by
doing very simple modifications... I am talking about radios that are not collector's items of
course ... For example, you may find at a hamfest, a fleamarket or a garage or yard sale an old
vacuum tube communications receiver... the cabinet may not be in very good shape, but the radio
looks rather clean inside... Then , go ahead and patiently remove and replace ALL, yes ALL the
electrolytic capacitors, and do the same, replace ALL, yes again, ALL the paper bypass capacitors
using the modern high technology mylar and epoxy bypass capacitors... Check all the vacuum tubes for
filament emission and transconductance, and take your time to re-align the receiver... You will be
pleasently surprised with the results.. BUT, never, and I mean NEVER, attempt to replace the vacuum
tube rectifiers with silicon diodes.... this may be done, but will require rewinding the power
transformer, in order to compensate for the increase in DC output voltage that results from the use
of low forward voltage dropping silicon rectifiers to replace the high vacuum diodes . You can also
improve those receiver's performance by providing DC regulated voltage to the filaments of the
oscillator tubes using state of the art solid state integrated circuit regulators... There are still
many of those radios all around the world, and you can benefit from their availability at low cost,
while also enjoying doing some electronic retroffiting to them !!!

........




You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and we do QSL here
100 percent... as a matter of fact we have QSLed back to all accurate signal reports since we first
went on the air 42 years ago amigos ... May Day of 1961, marks the day that our station used the
Radio Havana Cuba name for the first time ... So we are celebrating our station's birthday with a
party for all our staff and a very nice cultural event at one of Havana's most famous concert halls
, to be attended by all of our workers and their families... Now item four:

Computer generated radio noise... That is the question !!! And what a question amigos !!! What a
problem... but fortunately, there are many ways of reducing or attenuating computer generated radio
noise... For example, have you realized that there are some computers that are much more noisy than
others ? First of all, CRT displays, that is those using picture tubes generate noise more or less
proportional to the diagonal size of the screen... the larger the picture tube , the noisier the
display is going to be... SO, one very effective way of dealing with computer generated noise, is to
switch to the up to date solid state TFT displays, that do not use high voltage to operate, and for
that reason generate much lower noise levels... There are also some other tips that you may want to
keep in mind in relation to computer generated radio noise, but today, we are rather short of time ,
so will leave them for an upcoming edition of Dxers Unlimited... now, do remember that laptop and
notebook computers that use solid state displays are to the ones that are quieter, so if you ever
plan on using a computer for keeping your logs, or to operate on the digital communications modes,
by all means try to use a laptop or notebook instead of the classic desktop machines with CRT
displays !!!...

And now amigos, as always at the end of the show, here is Arnie Coro's HF plus Six Meters
propagation update and forecast...

The daily effective sunspot number SSN went UP dramatically during the last few days....reaching a
figure of near 100, while the daily sunspot count peaked for this 27 day rotation at 200 and has now
started to decline slowly. Unfortunately the higher solar flux has also come associated with coronal
holes that have generated Earth bound streams of charged particles that have caused geomagnetic
storms... As you hear this the most significant solar related event is that an active solar region
of sunspots has reached the delta magnetic configuration , and that may lead to the emission of the
powerful X type solar flares, when that specific area is located at a geoeffective position,so if an
X flare erupts, the resultant radiation first, and latter the ejected particles will be reaching the
Earth and may cause severe damages to orbiting satellites as well as radio and magnetic storms... So
be on the lookout for abnormal propagation conditions during the next three to four days . See you
at the weekend edition of the show amigos,and don't forget to send your signal reports, QSL requests
and comments about the program to arnie@rhc.cu, or VIA AIR MAIL to Arnie Coro , Radio Havana Cuba,
Havana, Cuba