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Re: [HCDX] Dxers Unlimited´s mid week edition for 12-13 August 2008
Radio Havana Cuba
Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited´s mid week edition for 12-13 August 2008
By Arnie Coro
Radio amateur CO2KK
Hi amigos radioaficionados worldwide ! You are listening now to the mid
week edition of Dxers Unlimited, our twice weekly radio hobby program.
I am Arnie Coro, radio amateur CO2KK and here is item one: After a high
speed solar wind event, the Earth´s geomagnetic field is expected to be
back at the extremely quiet levels that it has registered during the
extended second solar minimum now in progress… So the A index, the daily
geomagnetic disturbance indicator will be back to figures between one
and five units after Wednesday UTC day…. Item two: Doing antenna
maintenance work at my amateur radio station and listening post, so all
the three towers were stripped of the many wire antennas in order to
make it easier to paint them… But , that left me without any outdoor HF
antenna, something that was solved in just a few minutes by installing a
provisional inverted L and a 15 meters long ground radial acting as a
counterpoise… The provisional wire antenna loads up quite well on the 40
and 20 meters band, the two tested so far, and I am almost sure that
with the help of my wide range universal PI network antenna tuner, it
can also be used on 80 , 30, 17,.15 ,12 and 10 meters … As soon as I
have enough spare time to run the tests on the different bands, I´ll
tell you about the results in an upcoming edition of Dxers Unlimited…
From my past experience with odd length wire antennas, the minimum
length that will provide reasonable efficiency on the 40 meters band is
about 7 meters up in the air…that´s about 23 feet… An inverted L wire
antenna around 5 to 6 meters in length will work quite OK on the bands
above 10 megaHertz, but on 40 meters if simply would not be efficient
enough to make your signal heard at a reasonable level… Nevertheless,
there is always the option of adding a loading coil, that when placed at
a distance of no less than 3 meters from the antenna feedpoint, will
certainly help to make the short antenna work on the 40 meters amateur
band. Some time ago I wrote an article about a compact wire antenna
designed so that it will make the best possible use of a 7 meters long
wire, naming it the 7 meters long wonder antenna… I still have the
computer file of that article, and will gladly send it to Dxers
Unlimited´s listeners that are space limited for installing a short wave
antenna…
You can send your request for the 7 meters long wonder antenna file to
inforhc at enet dot cu, again inforhc at enet dot cu or VIA AIR MAIL to
Arnie Coro, Radio Havana Cuba, Havana , Cuba
Stay tuned for more radio hobby related information coming up after a
short break for station ID. I am Arnie Coro, radio amateur CO2KK in Havana…
………………………
You are listening to Radio Havana Cuba, the name of the show is Dxers
Unlimited and now here is our technical topics section of this mid week
edition …Today I will be discussing the latest events related to the
dreadful broadband over the power lines system, that is already causing
severe problems to radio reception at every location where it has been
installed. No matter what the sellers of those digital systems affirm
about the adding of selective notch filters that supposedly protect the
amateur bands from the horrible digital noise, the fact is that BPL, the
Broadband over the Power Lines also known by the name of Power Line
Communications or PLC is now under very careful scrutiny by
telecommunications authorities around the world, due precisely to the
harmful effects not only on amateur radio bands, but also on frequencies
devoted to public safety and even aviation related communications . Also
contributing to the BPL or PLC rejection is the fact that so far it has
proven not to be capable of providing the supposedly low cost reliable
broadband connections to Internet users… According to several recent
articles published by specialized engineering publications, not trade
magazines, the interference levels generated by the BPL systems are much
higher than the figures claimed by their designers. The most recent move
among the sellers of BPL systems seems to prove what engineers are
denouncing, as announcements are now made that BPL new systems are now
aiming at using microwave bands frequencies instead of the medium
frequency , short wave and lower VHF bands now used . At the same time
the lower cost and increasing ubiquity of fiber optics plus Wi-Fi ,
Wi-Max and similar technologies is acting as a deterrent to further BPL
deployments.
Amateur radio associations around the world are carefully keeping an eye
on BPL systems and Cuba is now exception with our national amateur radio
federation of radio clubs, the Federacion de Radioaficionados de Cuba
technical committee watching what is going on , as ETECSA, the national
telecommunications services provider enterprise is, like many other
similar companies around the world, exploring all available digital
distribution systems , including several of the BPL technologies options.
Digital equipment noise levels from computers and related equipment is
already at very high values in urban areas, making reception on the
range of frequencies from VLF to the top end of the VHF low band around
50 megaHertz more and more difficult.
Item four: Full size short wave curtain antennas are beyond the real
possibilities of the typical radio amateur operator, but some lucky guys
with a lot of real estate available and resources to set up those
antennas ,especially for the 10 and 6 meters bands where sizes are more
manageable , tell us that results are simply amazing, because the
curtain arrays not only provide a lot of gain but also have much broader
beamwidth than Yagi type antennas.
The key factor that provides the DX performance of a horizontal
collinear array is the Take Off Angle ( TOA ) .This is calculated easily
if you know the height of the lower set of dipoles from the ground. As a
matter of fact, the ITU standard antennas are described using that
parameter, for example, a 4, 4, 0.3 collinear will be used for short
range coverage, while a 4, 4, 1,0 will be the choice for a very low take
off angle ( typically 8 to 10 degrees above the horizon for the main lobe.
Because of the unsurmountable mechanical problems that come up if you
try to change the height above ground of the lower level of dipoles ,
there is no other choice but to install different antennas in the same
direction if you want to cover areas at different distances ( in the
same azimuth )...
There is a difference between broadband collinear arrays of dipoles that
are designed to cover a 2 to1 frequency range, for international short
wave broadcasting use they are typically made for covering 6 to 12 mHz
and 11 to 22 mHz ) or similar frequency coverages for other applications
with a reasonable standing wave ratio ( although you can assist them by
providing a set of several matching stubs at the base of the antenna
that can be switched remotely , in order to keep the SWR below 1.5 or so )
For amateur radio use, the bandwidth provided by a rather thin linear
dipole is more than enough to cover one band, although I remember a
contest station years ago that installed a 14 to 28 mHz 4 X 4 0,8
collinear and worked a lot of DX with it.
Another neat trick is to use a single wire reflector and place two
collinear arrays on the opposite sides... so you get two antennas for
the price of one passive reflector... two supporting structures, two
antennas, a single wire reflector and two main directions, that can turn
into SIX beams , if you add the easy to implement 15 - 0 - 15 degrees
beam slewing that is typically also switched by remote control from the
transmitter building.
The slight distortion of the horizontal radiation pattern will slightly
reduced the antenna´s forward gain, but when we are talking about 15 to
20 dB gain over a dipole, loosing 2 dB is of no concern !!!
One of the nice features of the curtain arrays is that they scale up and
down very predicticably , so they are an ideal teaching tool for
telecommunications engineering schools...
Designing broadband dipole elements for curtain arrays is another
fascinating aspect of this technology too !!!
………………….
Si amigos, ASK ARNIE, la numero uno, the most popular section of the
program is now on the air… Today´s question was sent by listeners in
Canada, the USA, Norway, the UK and Trinidad and Tobago… They all want
to know more about homebrewing receivers , transmitters and
transceivers, and how difficult this may be… As Karl from Oslo says in
his e-mail, the long Norwegian winter always keeps us at home a lot, so
devoting time to learning how to build radios is a quite logical step
after several years of short wave listening. Homebrewing radios and
electronic accessories required for short wave listening and amateur
radio use does involve a learning curve… It won´t be wise at all to try
to assemble a very sophisticated kit, like the ELECRAFT K3 transceiver ,
if you are not really familiar with soldering, identifying of electronic
components, and have a good understanding of circuit diagrams… You may
want to start your homebrewing adventures with simple circuits that
really work, and that won´t require a lot of debugging in case something
goes wrong. Among my favorite first time radios for someone just
beginning to homebrew equipment is the Moorabin Australian AM medium
wave band receiver, to which you can later add an audio booster
amplifier. The use of a high impedance Field Effect Transistor detector
provides much better performance than the typical two or three bipolar
transistors radios, and it also has much better selectivity. My dream
beginners radio for using on the amateur bands is the Polyakov detector
40 meters design by Michael Rainey AA1TJ, that has amazing sensitivity
and is very easy to build. The Polyakov antiparallel diodes detector
will not demodulate AM signals so the high power international broadcast
stations that operate on the seven megaHertz segment above seven
thousand two hundred kiloHertz will not be a problem. This little gem
can be improved by adding two easily built audio filters, one peaking
around 700 to 800 Hertz for CW reception and the other somewhat more
sophisticated filter involves a bandpass design that aims at providing
the best possible reception from 300 to 3000 Hertz, the band of
frequencies required for voice communications.
Si amigos, you can start by homebrewing even a crystal set, or a simple
Regenerative receiver, move up the ladder to the Polyakov detector set
and later add the audio filters to it… In a few months you will then be
able to target a more ambitious project, like assembling one of the
entry level kits that are now fortunately becoming available at very
reasonable cost. Assembling a good quality kit has many advantages, and
one of them is that your finished set will have the very nice look of
factory built equipment , something that according to my personal
experience is really hard to achieve when you homebrew from scratch…
…………
And now this announcement now from our engineering department amigos.
Following an analysis of the current HF propagation conditions and the
use of the short wave bands, we have decided to move our 6180 kiloHertz
transmitter that is used to broadcast daily towards Central North
America, to 6140 kiloHertz… Again, listeners in Central North America
can now pick up RHC on 6140 kiloHertz from 01 to 07 Hours UTC in
English, and on that same frequency we are broadcasting in Spanish from
00 to 01 Hours UTC. 6180 kiloHertz will now be used in Spanish to
Central America . And our morning Spanish language programs are now on
two new frequencies, 15120 kiloHertz beaming to 160 degrees from Havana
and 15360 beaming to130 degrees azimuth from Havana. The two new
frequencies for the morning program are beaming to South America, so if
you pick them up in North America , that´s the back of the main beam
Our evening programs in Spanish to South America are also on 13760
kiloHertz with the 160 degrees beam , and on 11680 with the 172 degrees
beam, so again, if you pick them up in North America, you are actually
on the back of the beams of the curtain arrays, that have a typical 25
to 30 dB front to back ratio…
And now at the end of the program, here is Arnie Coro´s Dxers
Unlimited´s HF plus low band VHF propagation update and forecast… Solar
activity continues at extremely low levels and the Earth is now moving
away from the high speed solar wind stream, so expect less background
noise, but the same low maximum useable frequencies of the extended
period of very low solar activity with the solar flux near 65 to 66
units and ZERO sunspots.
Sporadic E openings may be happening, even in the middle of the night,
but more typically during the mid morning and mid afternoon hours… For
meteor scatter propagation enthusiasts, the Perseids meteor shower will
provide chances to pick up many new TV low band channel stations before
the switch to digital TV in the USA make them go off the air forever…
Send your signal reports and comments about today´s program to inforhc
at enet dot cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba ,
Havana, Cuba
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