Dxers Unlimited weekend edition for 22-23 May 2004




Hi amigos radioaficionados !

Welcome to the weekend edition of your favorite radio hobby program, coming to you from sunny
Havana, where summer weather is providing us with beautiful days for going to the beach !!! I am
Arnie Coro, radio amateur CO2KK, your friend here in Cuba, now ready to read today's menu: ITEM ONE

Another interesting sunspot is growing in size at this moment, sunspot 618 may produce solar flares
during the next several days, and will certainly help to keep the solar flux at levels much higher
than what forecasters expected . ITEM TWO:TV DX season well in progress at this moment, with
sporadic E skip events happening all around North America, the Caribbean Europe and Northern Africa.
At least one recent sporadic E opening sent the maximum useable frequency up to the FM band, making
reception of FM stations from more than one thousand miles away possible even with handheld radios
and their telescopic whip antennas. More about the sporadic E season later .. ITEM THREE: Lost in
space. seems like the ultra sophisticated OSCAR 40 satellite is now a total loss, although some
ground control stations have reported some signs of the satellite trying to become active again
automatically. Remember that this was a unique satellite designed to orbit the Earth using a very
special elliptical orbit that would make it available for many hours at a time, just short of a
geosynchronous orbit, the so called MOLNYA orbit, is an excellent choice for any upcoming ham radio
satellite that will hopefully replace the doomed OSCAR 40, that had big problems from its very few
hours in Earth Orbit. ITEM FOUR: Listeners questions continue to come in via e-mail, postcards,
letters and fax messages, and I have quite a backlog of them here waiting to be answered. a recent
one from Chile, really surprised me, as normally the show is not heard so far South of Havana. But
the use of 11760 kiloHertz with our dipole antenna explains why English speaking listeners from
Chile are picking up Dxers Unlimited.. ITEM FIVE: More about low cost , easy to build ham radio
equipment, and at the end of the show, our exclusive and not copyrighted HF plus low band VHF from
30 to 120 megaHertz propagation update and forecast.Stay tuned for more radio hobby related
information, coming to you from Havana. Jose Costa Pupo is my sound engineer and producer here at
studio 6, I am Arnie Coro ready to be back with you in just a few seconds.

..

Si amigos, yes my friends, you are listening to Radio Havana Cuba, the name of the show is Dxers
Unlimited, and YES, we do QSL here one hundred percent, we do verify reception reports and we do it
absolutely free of charge, as all short wave radio stations should do. Send your signal reports and
comments about the program to arnie@rhc.cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba,

Havana, Cuba, And NOW , here is ASK ARNIE, THE most popular section of Dxers Unlimited, according to
your e-mails, postcards and letters amigos . QUESTION number one for today: From listener Scotty in
Maryland, Scotty wants to know why old radio magazines often mentioned the use of so called
converters ahead of short wave receivers to pick up the higher frequency bands. Well amigo Scotty, a
converter is nothing but a complete front end of a radio receiver, it usually includes a radio
frequency amplifier stage, a mixer and a local oscillator. The RF stage for the VHF bands used the
best available vacuum tubes that provided good gain and low noise, and the really good converters
used a crystal controlled local injection oscillator. Even today, adding a homebrew converter ahead
of a low cost receiver can provide outstanding results, especially with radios that lack front end
selectivity. Not too long amog amigo Scotty, I removed a lot of dust from a three vacuum tube six
meter band converter that was in storage for many years. it required 6.3 volts filament voltage and
150 volts DC to operate. Powering it up from one of my workbench power supplies , I connected the
more than 40 years old converter to a modern digital receiver, and was pleasently surprised when I
could pick up several of the local VHF communications systems operating here around 49 megaHertz,
using just a test lead from the multimeter as an antenna. Converters are no longer required for all
practical purposes, as modern HF receivers are including extended tuning range up to the two meters
amateur band. Anyway, for those of you like amigo Scotty that are interested in VHF converters, I
may add that they are not too difficult to homebrew, especially if you use solid state devices . A
typical more modern converter will use a high gain low noise MOSFET RF amplifier stage, a double
balanced passive mixer and a bipolar transistor oscillator. It will be powered from 12 volts DC and
when connected to even a low cost modern digital receiver, will turn the resultant combination into
a rather nice VHF receiver , useful for monitoring 6 meters during the summer sporadic E season.
Remember to tune set the receiver to scan from 50.0 to 50.3 megaHertz where most of the activity on
6 meters is concentrated around the world. QUESTION TWO, Came from Montego Bay in Jamaica, listener
Randy , who listens to our 9550 kiloHertz Caribbean edition, tells me in his e-mail that he wants to
know more about the magnetic loops and why are they so useful when used at noisy locations. Well
amigo Randy, magnetic loops are first of all compact antennas, they are easy to turn around the
compass to cancel noise sources, and above all, receive only magnetic loops can be built very easily
and at low cost by anyone . My ultra simple HULA HOOP MAGNETIC LOOP is a perfect example of what I
am talking about. It is built using a toy HULA HOOP , a length of TV type coaxial cable, and a
receiving type variable capacitor. It takes less than a couple of hours to complete, and most of
your construction time will be used building the base where the HULA HOOP is fixed, so that it may
be rotated. My HULA HOOP MAGNETIC LOOP provides excellent reception from 10 to 30 megaHertz, but it
also works quite well with powerful station from 5 to 10 megaHertz. Amigo Randy, I am sending direct
to you via e-mail the complete , step by step building instructions for my HULA HOOP MAGNETIC LOOP,
so that you can start building yours and then tell me also via e-mail how it performs at your
location.

The HULA HOOP MAGNETIC LOOP is possibly one of the lowest cost high performnce indoor antennas that
exists, but it can also be used outdoors too, in which case you will have to install a remote tuning
system to move the air spaced variable capacitor setting according to the operating frequency that
you want to use. Let me add that the HULA HOOP MAGNETIC LOOP tunes quite sharply and it does require
constant retuning of the air spaced variable capacitor with even a very slight change in frequency.
BUT, peaking the antenna tuning for maximum signal is quite easy to do, and at the same time it
provides ultra-sharp selectivity right at the antenna, that helps a lot to reduce unwanted noise and
cross modulation problems caused by high powered stations that affect low priced receivers so badly.
As a matter of fact, using my HULA HOOP MAGNETIC LOOP with a low cost digital receiver proved to be
a very interesting experience, as the radio's performance was enhanced signficantly due to the extra
selectivity at the front end provided by the magnetic loop antenna system.

QUESTION THREE, yes, one extra today to reduce the backlog a bit, well question three, sent by
listener Carlos here in Havana, he wanted me to describe the design parameters for the low cost two
element antenna for the 2 meters amateur band. Well amigo Carlos, using standard TV antenna elements
aluminum rods, the small YAGI uses a split driven element of 980 millimeters, fed at the center with
50 ohm coaxial cable. The boom is made from PVC pipe of the type used for water distribution , and
the reflector element is 1002 millimeters long and located at exactly 51 centimeters from the driven
element. This antenna has around 4 dB gain, a broad radiation pattern, is rugged and easy to build
and will help you to access distant repeaters that can't be reached using the typical handie-talkie
helically loaded antenna, popularly known as rubber ducky because they look like the tail of a duck
wagging !!!

Again, here are the dimensions for the 2 element low cost, easy to build YAGI for the two meters
amateur band, the driven element is 980 millimeters long and split at the center, you may want to
make it a little shorter if you plan to use the antenna for the segment of two meters between 146
and 148 megaHertz.The boom of the antenna is made from PVC pipe of the type used for high pressure
water distribution, and is one meter long, so that you can hold the antenna to any support from the
rear of the reflector element.

The separation between the driven and the reflector element is 51 centimeters, and the length of the
reflector element is 102 centimeters, that you can make a little shorter for the upper two megahertz
of the two meter band.

I feed this antenna with 50 ohm coaxial cable, and right after the feedpoint, I wind 8 turns of the
coaxial cable to the boom of the antenna to make an RF choke.. the cable is then fed trough a hole
in the boom to the rear of the antenna where it exits . I have made many of these antennas, and
found out that they provide excellent performance, and when built using the above mentioned
dimensions they are usually below 1.5 to 1 standing wave ratio even before any adjustments are made.
They can be adjusted for almost perfect standing wave ratio by sliding the reflector element back
and forth across the boom, and then leaving it permanently at the spot that provides the lowest SWR.
Remember to use TV antenna rods or tubing, as the dimensions for my low cost two meter YAGI just
described are based upon the diameter of the typical TV antenna elements.

Try to tune the antenna for minimum SWR using a VHF standing wave ratio meter, but again, you can
use the antenna directly without any adjustments without fear of high SWR, by just carefully
measuring the elements .

And now amigos, as always, at the end of the program, here is Arnie Coro's Dxers Unlimited's HF
propagation update and forecast. Solar flux is hovering around 110 units and the A index was still a
bit high around 12 units, but hopefully it will go down later in the week after the effects of the
high speed solar wind go away. Sunspot active region 618 is developing, and it may produce flares
during the rest of the week as it transits across the solar disk. Sporadic E openings are going to
be plentiful, surprising, interesting and challenging during the next few days, so monitor the low
band TV channels for them. If you have a 10 meters or 6 meters band amateur radio rig, keep it on
during the time that you are at home, keep them scanning from 28 to 28.5 megaHertz and from 50 to
50.3 megaHertz for signs of openings, that in many cases will be detected when automatic beacons
start to come in as the opening starts . See you all at the mid week edition of the program and don'
t forget to send me your radio hobby related questions, signal reports and comments .. send mail to
: arnie@rhc.cu, or via air mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba