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Re: [HCDX] Dxers Unlimited's script for May 12-13 2007 weekend edition
Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited’s weekend edition for May 12-13 2007
By Arnie Coro
Radio amateur CO2KK
Hi amigos radioaficionados, welcome to the weekend edition of Dxers
Unlimited, which today will feature a re-run of an Antenna Topics
section about the HENTENNA, as requested by a large number of listeners
around the world that have written to me recently, as this Japanese
antenna seems to be making headlines in radio publications around the
world once again…
By the way, the original report here at Dxers Unlimited, dates back to
1999,more precisely, it went on the air the 12th of October of 1999, and
according to my records, it generated a lot of interest from our
listeners, who were at that time, 1999, getting ready to enjoy the peak
years of solar cycle 23 !!!
So here is once again at the request of Dxers Unlimited’s fans , the
report on the HENTENNA, the Japanese elongated loop antenna with an easy
match to coaxial cable feedlines of any impedance, be it 50, 60 ,75 or
93 ohms...or even 150 ohms !!!
I recently built yet another HENTENNA for the FM broadcast band, and it
is working nicely, having already pick up some Sporadic E skip DX
stations from Mexico, the US and Puerto Rico during the just starting E
skip season now in progress.
Once again, remember that the HENTENNA produces or receives VERTICALLY
polarized waves when the antenna is placed horizontally; that is, with
the long sides of the loop pararell to the ground. AND, if you want
horizontal polarization, just flip the HENTENNA so that the long sides
of the loop are vertical, and the short sides are parallel to the
ground, something that is puzzling, but that’s the way it is amigos…
By the way, one of the world's foremost antenna experts, Dr. L. B.
Cebik, amateur radio operator W4RNL, has done an extensive analysis of
elongated loops, and his findings are really fascinating. Dr. Cebik
specializes in computer modeling of complex antenna systems, and his
work with the HENTENNA and other similar elongated loops shows that the
HENTENNA is a very good performer indeed.
For the benefit of those who could not pick up last weekend's Dxers
Unlimited edition, I will repeat the formulas for calculating HENTENNAS
in the frequency range from 14 megaHertz all the way up to the high TV
band that here in the Americas ends at 216 megaHertz.. so amigos, stay
tuned, I'll be back with more radio hobby related information in a few
seconds...
……………….
You are listening to Radio Havana Cuba, the name of the program is Dxers
Unlimited… you can send your signal reports and comments via e-mail to
arnie@xxxxxx or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba…
And now more about the HENTENNA. Dr. Cebik's computer modeling shows
that the elongated loop HENTENNA has an edge over a regular square one
wavelength loop and the regular elongated loop.
HENTENNAS for receiving FM broadcast signals are very easy to build,
using a wooden or PVC pipe frame and copper wire. I built the one just
mentioned cut for 100 megaHertz, using PVC insulated no. 12 wire, the
one that is typically used for home wiring.
The loop was closed by soldering with a butane torch, and using regular
solder with rosin core... The reason for using the butane torch is that
no soldering iron at hand here could handle the heavy wire PLUS the high
speed heat transfer of the copper wire.
The loop for the 100 megaHertz antenna is 1.5 meters on the long sides
of the rectangle and 50 centimeters on the short sides. The feed point
for the 50 ohm cable is located about 55 centimeters from one of the
short sides of the loop.
The antenna is installed with the long sides in a vertical position; for
receiving horizontally polarized FM broadcasts. I tried both 50 ohms and
75 ohms coaxial cables, and could not detect any difference on the
weakest station that I am picking up here regularly with the FM band
HENTENNA.
Again, if you want to make of these elongated loops for receiving, here
are the measurements to use: for the long sides of the rectangle 1/2 of
a wavelength at the operating frequency, for the short side, the length
is 1/6 of a wavelength... and the connection point for the coaxial cable
of 50 ohms impedance is a little more than 1/6 of wavelength from one of
the short sides of the rectangle.
I have tried two different techniques for feeding the antenna, one using
two wires connected to the long sides and going to an insulator to which
the coaxial cable is attached... this is what I do with antennas for the
lower frequencies.
For the higher frequency antennas, like for example the TV HI VHF band,
or the amateur two meter band, I use the coaxial cable itself, by
carefully splitting the center conductor and the shield in two... it
takes a little practice to do, but you will be able to do it, and it
saves time and avoids one extra soldered connection.
Do remember to fully protect the coaxial cable from the weather, by
sealing it properly with PVC tape and silicone sealing compound...
HENTENNAS can be built for any frequency between 10 megaHertz and 300
megaHertz by using heavy WIRE, and for the frequency range from about 50
megaHertz to 500 megaHertz you may try building HENTENNAS with copper or
aluminum tubing.
YES amigos, this is yet another easy weekend project... collect all the
needed materials and have them ready at your workshop, the garage or
near the kitchen table, so that this coming weekend you can build your
own low cost elongated loop HENTENNA.
Remember, if you are a radio amateur, that a HENTENNA is a very
effective antenna to take along with your HANDIE TALKIE, as it will
extend the range of the HT many times. I now have my portable HENTENNA
for 2 meters that has shown a gain of more than 6 to 10 decibels above
the handie talkie's rubber duck antenna.
In other words, the HENTENNA is behaving as if you add a linear
amplifier to the HT with the additional benefit that if DOES NOT USE UP
EXTRA battery power. And one final comment, do remember that the
HENTENNA is DIRECTIONAL, so you can turn it around for best possible
signals... A HENTENNA for two meter band FM must be installed with the
long sides HORIZONTAL... in order to receive and transmit the vertically
polarized waves used for amateur 2 meter FM communications!
Now our next item, here at the weekend edition of Dxers Unlimited: Radio
amateurs running extremely low power transmitters are demonstrating that
the ability of the ionosphere to send back to Earth radio signals is
much better than what was previously thought.
Running powers as low as 10 milliwatts, that is 20 db down from a 1 watt
transmitter; two way contacts on the 20, 17,15 ,12 and 10 meter bands
are nowadays quite regular... According to the experimenters involved in
this fascinating milliwatting tests, when power goes down below about
100 milliwatts, QSB or fading is very severe, indicating that this may
be very near the lowest possible limit for ionospheric propagation using
standard CW Morse code.
Using coherent CW or other computer-enhanced signal processing, it now
seems like ultra-low power signals of 1 milliwatt or even less may be
effectively used. Anyway, this is one more reason to join the ranks of
those amateur radio operators who have decided to do their operating at
low power or QRP levels... 5 watts on CW and 10 watts on SSB are
nowadays more or less universally accepted as the maximum power for QRP
stations.
And one final comment about the ultra low power transmission
experiments... 1 watt to 5 Watts power output transmitters can be built
using very easy to obtain receiver type components, something that will
allow many amateurs in less developed areas of the world to join us. One
of the things that keep many potential radio amateurs from going on the
air in less developed countries is the lack of appropriate transmission
type radio components.
With the QRP rigs, a defunct TV set, a dead boom box, or any other
otherwise broken down or junk electronic gear may become the source of
all the parts needed to make a homebrew radio station.
………..
Six meters opening up again via sporadic E, according to reports
received from Europe, North America and the Caribbean, plus my own daily
observations, the sporadic E clouds are once again providing that very
interesting propagation mode for TV and FM band Dxers, and of course, to
amateur radio operators too...
The 30 meter amateur band operator is now becoming more and more popular
during the low ebb of the solar cycle, because 20 meters is closing up
much earlier due to the very low solar activity. Installing a 30 meter
band elongated loop is easy , and offers excellent performance for DX
work...
The 30 meter band elongated loop antenna,is also simple to build,
matches 50 ohm coaxial cable without any problems, or if you prefer it
can be fed with open wire transmission line and then be useful on
several bands for transmitting and short wave listening too. Do not
forget that many amateur radio operators also enjoy listening to
international short wave broadcast stations too, and that we use our
amateur radio rigs to enjoy that aspect of the hobby too.
Well, here is some information about this rather compact antenna, that
radiates with a low departure angle, despite the fact that it does not
need very high masts, as a matter of fact, you can use home brew masts
made from bambusa-bambusa linnei, well bamboo, bambusa-bambusa linnei is
the scientific name that botanic experts give to bamboo.
Masts used by Cuban radio amateurs for this antenna are made of several
sections of heavy cuban bamboo or cana brava, reinforced between
sections by short lengths of aluminium tubing of appropiate diameter.
The masts are some 9 meters high, or for those of you that still think
in English measuring units almost 30 feet high. .
The rectangular loop's vertical sections are 5 meter high, and the
horizontal sections are 10 meter long. So, the loop is shaped like a
rectangle that has its short sides of 5 meters length, and the long
sides of 10 meters length. The short sides are the vertical ones, so
that allows the lower horizontal section to be placed at 4 meters above
ground, which is certainly not ideal,but is nevertheless good enough to
make the loop generate an adequate vertical take off angle for DX work.
Now, listen how the antenna is fed... The 30 meter band loop is fed
using 50ohm coaxial cable, but you can use low cost TV type 75 ohm coax
if you wish too. The feedpoint is at one of the upper corners of the
antenna, as we want to take advantage of the elevated feedpoint placing
the high current as high as possible!!!
As I said a while ago, the 5 meter high and 10 meter long rectangular
loop can be also fed with open wire line, something that will allow its
use on other frequencies too. Using the coaxial cable feedline, the
antenna is a single band antenna, capable of low SWR or standing wave
ratio operation only on the 30 meter ham band that spans from 10.1 to
10.150 megaHertz. Similar aspect ratio loops can be designed and built
for other amateur bands, and they offer to their users several important
advantages over the classical single band half wave dipole.
The first and most important one is that the rectangular loop is a very
quiet antenna for receiving purposes, due to the fact that it is a
closed element, then add to this that it does not need very high masts,
plus that even when placed at a relatively close distance from ground,
it does generate a nice and clean, low take off angle vertical pattern
which is much better for DX work than the vertical pattern of a half
wave dipole at the same height. Now, add to all this advantages its low
cost and very easy installation, direct coaxial cable feed using either
50 or 75 ohm cable, and you will realize that the rectangular one
wavelength loop is a very nice all around antenna.
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