Radio Habana Cuba
Dxers Unlimited
Dxers Unlimited's mid week for 25-26 October 2005
By Arnie Coro
radio amateur CO2KK
Hi amigos radioaficionados ! I am Arnie Coro, radio amateur CO2KK, your host
here at the mid week edition of Dxers Unlimited... Nice to have you
listening to this program or reading the script at our world wide web site,
or if you are a subscriber of the ODXA mailing list, the Ontario Dx
Association , then you can also read this show's script because I upload it
to the ODXA list as soon as it is finished... Now here is item one, a news
item... SUNSPOT COUNT is ZERO, yes, you heard it right, an absolutely blank
SUN today... no sunspots, and that of course means very low solar activity..
But the K index was a bit on the high side because of a shower of protons
reaching the ionosphere coming from a coronal hole... More about HF and low
band VHF propagation conditions as always at the end of the program... Item
two... our emergency communications networks still operational here, because
western Cuba has now entered into the RECOVERY PHASE, and communications are
as important now as they were in the middle of the hurricane.... Amateur
operators here in Cuba were deployed in many places to provide in some
instances back up communications to other systems, and in other places , the
ham stations were the only way that vitally important information could be
conveyed to the civil defense centers. Item three: Low cost easy to obtain
from the telephone company pararell wires downlead is now in use by many
Cuban radio amateurs , and results are very good indeed, listen to our
technical topics section today and you will learn how to install your
permanent or emergency radio station using this low cost downlead... Ask
Arnie will also be on the air today.... Now standby for a few seconds... if
your radio uses the analog tuning system, check for the best possible tuning
and if your radio is digital, then it's time to put this frequency on one
of your receiver's memories !!! This is Radio Havana Cuba...
......
Si amigos, you are listening to the mid week edition of your favorite
listener oriented and technicaly minded radio hobby program, Dxers Unlimited
with Arnie Coro, radio amateur CO2KK... and here is item three in detail...
When the telephone company uses overhead cabling, it has to connect the
junction box, located at the wooden, steel or pre-stressed concrete posts ,
with you home. This is done using a very rugged and highly reliable dual
conductor line... Here in Cuba that type of line is locally made , at the
ELEKA Electric Wire manufacturing plant, and not too long ago I got in touch
with the technologist of that Havana province industrial plant. I asked him
about the characteristics of this type of telephone connecting dual line,
and he told me that it used very high quality polyethilene insulation, and
pure copper conductors.
When I asked about the radio frequency impedance of that cable at different
frequencies, the senior engineer made a pause, and told me... Coro, we don't
know... and the reason we don't know is that this type of cable is intended
to connect from a pole located junction box to a building, carrying just
direct current that comes from the telephone exchange, and audio frequency
signals... So, here at ELEKA we have never measured the "bajante telefonico"
that is the telephone downlead, for radio frequency impedance or
attenuation at different frequencies, and he added, I already know that
several radio amateurs are using it very effectively, so why don't you ask
the people at our telecommunications national laboratory to measure this
type of cable. And that's exactly what I did, with the help of three other
amateur radio operators, who happened to work for that facility... We
decided to carry on a very comprehensive series of tests and the results
were very interesting and encouraging indeed...We found out that the twin
wire polyethilene insulated telephone company downlead had an average
impedance at the very popular in Cuba 7 megaHertz or 40 meters band of
around 110 ohms...the many measurements that we carried on had a spread
between 100 and 120 ohms ... so we decided to consider this downlead as a
115 ohms impedance at 7 megaHertz pararell transmission line... We also
measured at other frequencies, and to our surprise , due to the high quality
of the polyethilene insulation used,the impedance was quite constant up to
the 2 meters or 144 to 148 megaHertz amateur band.... As the tests were in
progress, we proceeded to measure the attenuation per unit length, and again
to our surprise we found out that even on frequencies as high as 200
megaHertz the attenuation was quite low...
In order to use this type of transmission line with standard amateur radio
equipment that have a 50 ohm asymmetrical coaxial output and input , we have
built a very simple antenna coupler that performs triple duty... It serves
to adapt the 115 ohms impedance of the pararell transmission line to 50 ohms
at the same time the output of the antenna coupler or tuner provides an
assymetrical 50 ohms output for the transceiver, and last but not least, the
pararell tuned circuit provides additional harmonic rejection ... At CO2KK ,
my ham radio station I went a step further, by installing a four to one
balun between the 115 ohms pararell transmission line and my standard
homebrew PI network antenna tuner... If you divide 115 by 4, you will obtain
an output impedance of around 28 ohms, that is very easy to match with my
antenna tuner...The transformation from pararell or symmetrical transmission
line to a coaxial line is done by the four to one balun, that I connect with
a short length of 50 ohms coaxial cable to the tuner... Attenuation
measurements done at 7 megaHertz showed that the phone company downlead has
less than 1 decibel loss per 30 meters or 100 feet length... so for the
typical ham station, this low cost solution is an excellent choice to
replace the expensive coaxial cables ...
Later we worked on a similar idea to use the phone company downlead on the
two meters or 144 to 148 megaHertz band, and it also worked quite well, by
means of a simple PI network tuner and a four to one balun wound on a
ferrite toroid core... If your figure out that the phone company downlead
can be obtained just for the time spent asking for it from the local
repairmen, then you can see why it is becoming so popular among Cuban radio
amateurs !!! By the way, the phone company repairmen provide us with short
lengths of that type of downlead that are at the end of the reels and are
just "too short" to be useful for them to install...
........
You are listening to Radio Havana Cuba, the name of the show is Dxers
Unlimited and here is ASK ARNIE, our number one top favorite section of the
show... Amigo Bruce Atchinson, a faithful long time Canadian listener sent
an e-mail telling me that the Bayliss clockwork generator radio that he owns
was a very rugged one indeed, as it had fallen from the top of a high piece
of furniture and still works... Bruce has now problems with this HF short
wave bands amateur radio antenna, and due to his limitations with his sight,
he cannot climb to the rooftop to fix it... Amigo Bruce, I am sure that you
will very soon find a local ham radio operator that will visit your home and
fix up the antenna so that you can continue to enjoy the HF bands !!! And
now today's question, it came from no less than eleven listeners, and they
all have asked me to talk a bit about the very low profile HF antennas
mentioned a few weeks ago here. Well amigos, all I can say is that the so
called EMGP, or electromagnetic ground plane antennas do work, and if
properly installed using a highly effective ground system, and then properly
adjusted for maximum efficiency, they work amazingly well. My test antennas
are now operating on the 50 megaHertz or 6 meters band , and the 144
megaHertz or two meters band, and they both perform with almost the
efficiency of a full size quarter wave vertical over a ground plane... The 6
meters antenna works nicely for local contacts, as it is omnidirectional and
has a low take off angle, concentrating the radiation very close to the
horizon, exactly what you want for local ground wave communications, but
comparisons with a standard half wave dipole at the same height show that
when six meters is open for sporadic E skip, signals on the low profile EMGP
antenna are lower by anywhere between 3 and 9 decibels, something that
confirms that the EMGP is a low angle radiating system indeed.
My very compact 2 meters EMGP is a very low profile antenna... A full
wavelength at 145 megaHertz is 2.0652 meters, and the homebrew EMGP I am
testing here is only 10 centimeters high, almost a fifth of the height of
the standard quarter wave vertical monopole used for comparative tests. The
two antennas can be placed at the center of a solid aluminum plate that has
a 55 centimeters radius, that according to antenna gurus is an ideal ground
plane for all practical purposes..I placed the EMGP at the center of the
ground plane and asked a local ham operator to mark the signal intensity of
the received signal... I also recorded the intensity of the signal that I
was receiving. Then , I changed antennas, and ran a similar test... Results
showed that both antennas provided almost exactly the same signal intensity.
.and running that test routine many times and with many different stations,
confirmed that both antenna's had practically the same efficiency...
The EMGP is made using number 8 AWG pure copper wire, and the quarter wave
vertical is made using a 6.25 millimeters or quarter inch solid copper pipe.
Later I ran another set of tests, using a ground system formed by sixteen
number 14 solid copper wires, and results , for all practical purposes were
identical. If you want ot learn more about the low profile, easy to build
and to adjust EMGP antenna family,
just send me an e-mail to arnie@rhc.cu, again arnie@rhc.cu, and I will be
more than happy to supply you with information about these unique antenna
systems that are becoming now popular even among AM broadcast stations...
And now just before QRT , here is Arnie Coro's Dxers Unlimited exclusive and not copyrighted HF plus low band VHF propagation update and forecast... Strange Sporadic E openings across the Gulf of Mexico as Hurricane Wilma was hovering over Yucatan and then moving fast towards FLorida may be related to thunderstorm activity... Solar flux very low, just barely above 70 units, the A index was also very low, but the K index at higher latitudes was up to 4 recently due to the effects of the coronal hole... Best daytime frequencies for DX are between 15 and 25 megaHertz, and at night the best DX conditions will be between 6 and 12 megaHertz... Don't forget to listen to the weekend edition of Dxers Unlimited, and after you finish listening drop me an e-mail and tell what you liked, and what you didn't like about today's program... Send mail to arnie@rhc.cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba