Re: [HCDX] Dxers Unlimited's weekend edition for 10-11 February 2007

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

Dxers Unlimited weekend edition for 10-11 February 2007

Hi amigos radioaficionados !
Welcome to the weekend edition of your favorite radio hobby program, 
coming to you from sunny Havana, where our mild winter 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
ITEM TWO:TV DX off season openings have happened, recently, with 
sporadic E skip events around , the Caribbean. 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
That is still several weeks away, due to start at the end of April as 
usual .. ITEM THREE: An amateur radio 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 new 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 omnidirectional 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 , 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@xxxxxx, 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,that is built as a separate unit, 
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 or use a single intermediate frequency, the so called single 
conversion receivers. Not too long  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 portable receiver,the SONY ICF7600 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’s very sharp tuning.
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 75 units and the A index was still a  around 6 units, 
and it is going to move up later in the week.Solar flares are not 
expected during the rest of the week .But propagation conditions will 
take a turn for the worst  because late on 11 February UTC day, a 
recurrent coronal hole high speed stream is expected to become 
geoeffective with periods of active to minor storm levels possible. 
Predominantly unsettled to active conditions are expected on 12 February 
due to the coronal hole.
Sporadic E openings are going to be very rare, but do monitor the low 
band TV channels for them. ns 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@xxxxxx, or via air mail to Arnie Coro, Radio 
Havana Cuba, Havana, Cuba

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