Radio Habana Cuba
Dxers Unlimited
Dxers Unlimited's weekend edition for 23-24 April 2005
By Arnie Coro
radio amateur CO2KK
Hi amigos radioaficionados ! This is the weekend edition of Dxers Unlimited
reaching you as the number of sunspots is very 30, and the solar flux is
barely seven units above what's considered to be the baseline of solar
activity ...Nevertheless, Saturday just an hour after my local noon timeI
was able to pick up several 10 meters amateur band beacons, indicating that
the band was open to parts of South America, North America and the Caribbean
.. So, if you have an amateur radio transceiver capable of operating on the
10 meters band, start monitoring between 28.1 and 28.3 megaHertz for signals
coming from beacon stations... They will usually give an automatic CW Morse
code ID and their location... As a very good friend of mine, who is a 10
meters band fanatic, tells everyone at the radio club... ten meters is open
much more time that what anyone can imagine, what we all radio amateurs need
is that operators make more CQ DX calls , even when the band seems to be
closed, and of course, keep on calling if you happen to hear at leas one
beacon station... By the way, now that the solar cycle is approaching its
end, my perception is that in many countries the price of single band 10
meters band transceivers will drop down dramatically. Those radios are
typically a spin off from Citizens Bands production runs, and many of them
are excellent performers and a real outstanding buy... I have one of them
here at CO2KK, its a Radio Shack HTX100 single band transceiver originally
made by UNIDEN... It's very well built, rugged and reliable, and when 10
meters is not open, I use it as an intermediate
frequency for VHF and UHF bands converters !!! And talking a bit more about
the 10 meters band... even now that the effective sunspot number is below 20
 the band opens up for DX during local daylight hours !!! The rest of the
time 10 meters is an excellent band for QRM free local chats !!!
Stay tuned for more radio hobby related information amigos !!! Here at Dxers
Unlimited, the program that tries to provide you with the most up to date HF
plus low band VHF propagation updates and forecasts..
I am Arnie Coro in Havana ....
......
Si amigos, yes my friends... a ten meters band antenna fits almost anywhere.
. I have recently built a 60 centimeters high, that is about 2 feet high
vertical antenna for 10 meters, to demonstrate my fellow radio club members
that local, and even DX contacts are possible with a very compact ten meters
band antenna... I have tested this antenna by comparing it with a regular 2
5 meters high, that's about 8 feet, vertical antenna. In both cases I used a
minimum number of ground radials... and very short ones indeed, just 60
centimeters long for the short antenna, and 2.6 meters of 8 feet and 4
inches long radials for the "full size" quarter wave vertical.
The practical tests consisted in placing the full size antenna in the middle
of my terrace, installing the radials and asking for signal reports, both
from local and DX stations. Then the full size vertical was removed as well
as its four radials and the ultra compact sixty centimeters high vertical
and its also sixty centimeters long radials were installed at exactly the
same place... Now, don't be surprised to learn that in many instances the
operator at the other end could barely note the difference...as actual field
intensity measurements done later with a professional
and properly calibrated field strength meter, showed that the ultra compact
antenna was just minus 2 dB below the field intensity of the full size
vertical, and that amigos is barely a third of an S unit... as each S unit
is the equivalent of a 6 dB change in signal intensity... I'll tell you more
about the ultra compact, experimental 10 meters band vertical in just a few
seconds...
.......
A 10 meters band vertical antenna that is just 60 centimeters high ? Is that
really possible Arnie ? Those where the questions asked by my fellow radio
club members when I showed them the strange looking antenna... More
questions followed... for example, Arnie Jr. CM2KW my elder son asked what
was the purpose of the funny looking copper tubing spiral at the top end of
the antenna... because he had seen some other of my antenna designs in which
I used a large circular plate as a capacity hat, but was surprised with the
copper spiral.. Arnaldito, I said, Arnaldito ( that's little Arnaldo in
Spanish, the copper tubing spiral is doing two jobs at the same time... it
is acting as inductive loading, and at the same time it acts also as a
capacity hat for the antenna.
The ULTRA COMPACT is split into four easily assembled and disassembled parts
. The base section, the loading coil at the middle of the antenna, and the
top section t of the vertical element are joined using a very reliable and
low cost method... that is small clamps of the type used to keep flexible
hoses properly connected to sections of pipe... The fifth part of the
antenna is the copper spiral, that is joined to the top section. From four
to sixteen short radials extend around the base of the antenna, and when
asked by Julio an avide antenna builder, I told him that short antennas do
not seem to require the use of quarter wave radials, as both theory and
practice demonstrate...
So, for you to have a clear picture of the ULTRA COMPACT... it has a base
section to which the 50 ohm coaxial cable feedline is attached, and that
base section is provided with from four to eight bolts and nuts to which the
radials are connected.
At the top of the base section the center loading coil is attached, and at
the upper end of the coil, the second 30 centimeters long part of the
radiator is attached.
The final part of the assembly consists in attaching the copper spiral to
the upper section...
After playing around for almost a complete weekend with the ULTRA COMPACT
antenna I realized that it's a very good idea to make the two vertical
sections of large diameter copper tubing if possible, or if it is not found,
you can use aluminum tubing of diameters between 6 and 37 millimeters, that
is from about a quarter of an inch to an inch and a half diamter...The top
loading copper spiral is made from flexible copper tubing of around 6
millimeters in diameter, and it is held together using sections of low loss
polyethilene .
After the antenna is built you have just enjoyed half of the fun !!! You
must then install the ULTRA COMPACT and start tweaking it for minimum
standing wave ratio, always remembering that compact antennas are very
sensitive to the objects that sorround them... that's why I use sliding
tubing, so that the actual physical dimensions of the antenna can be changed
very easily, by just untighting a clamp, extending or shortening the element
 and then tightening it up again.
My ULTRA COMPACT a bit more than 2 feet high,that's about 60 centimeters,
vertical antenna for the 10 meters band, has already allowed me to work 22
countries while running about 20 Watts peak envelope power... and typical
signal reports from DX stations move between S5 and S9 PLUS, pretty nice for
such a small antenna that has such a footprint that it can be fitted almost
anywhere... It's also an excellent balcony antenna, that you can assemble in
a few minutes, and put it back in storage after finishing working some
locals or DX stations. A similar antenna for the very popular 20 meters band
is about one and a half meters high, and tests are now in progress here to
have a clear picture of how it works... Radiation efficiency as compared
with a standard quarter wave vertical antenna will be anywhere between 25
and 50 percent, that is minus 6 to minus 3 decibels, a rather good figure if
you consider that one S unit step is 6 dB, so even in the worst possible
scenario, my ULTRA COMPACTS inductively and capacitively loaded short
verticals are a pretty attractive option for those of you that are short of
space for installing full size antennas...
Last but not least... if you make the top loading copper pipe spiral
carefully, the complete antenna has the additional attraction of passing
like yet another modern art sculpture amigos !!! If you want to learn more
about the ULTRA COMPACT single band short verticals for the 10,15 and 20
meters amateur bands, just drop me an e-mail or a postcard to arnie@rhc.cu,
again arnie@rhc.cu and VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana
 Cuba.
....
You are listening to Radio Havana Cuba, the name of the show is Dxers
Unlimited, and here is our next item of this weekend edition...our popular
technical topics section of the program. Today I'll tell you about MOV.s yes
M O Vs, or metal oxide varistors, a form of non linear resistors that is now
present in practically all well built electronic equipment because they
provide excellent protection against voltage spikes and transients..M O Vs'
come in a variety of voltages and currents ratings, and it's always a good
idea when you work with older equipment at the workshop to add at least one
of two MOV's to them for additional protection. The MOV's look like a large
sized ceramic disk capacitor, but they are really an electronic marvel
because they will show a high resistance until a voltage spike comes in, and
then the MOV transforms itself into an instantenous short circuit, sending
to ground the peak that may do a lot of damage to your radio and electronics
equipment amigos !!!
And now just before going QRT here , listen to our exclusive and not copyrighted HF plus low band VHF propagation update and forecast... Solar flux is very low indeed, with the flux index barely above the baseline activity of the Sun... There are chances of increased solar activity during the next few days, but don't expect sunspot number much about 70 or so, as the cycle is keeping its downward trend following its path towards the 2006 to 2007 minimum... My advice is to make keep monitoring the 10 meters band beacons during your local daylight hours, and concentrate on the frequency range between 1.8 and 12 megaHertz during the local nighttime at your QTH amigos... See you at the midweek edition of the program !!! I am Arnie Coro in Havana, and it was certainly my pleasure to have shared with you the past seventeen minutes or so .....