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Re: [HCDX] Dxers Unlimited´s mid week edition for 10-11 June 2008
Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited´s mid week edition for 10-11 June 2008
By Arnie Coro
Radio amateur CO2KK
Hi amigos radioaficionados around the world and in space… I am Arnie
Coro,radio amateur CO2KK, your host here at RHC´s twice weekly radio
hobby program. Now here is item one: Extremely low solar activity
continues, with the effective sunspot number reaching just 2 units
during the Monday morning hours local time in Havana, that is from 11 to
15 hours UTC. All the world´s ionospheric vertical incidence sounders
are registering a very weak ionosphere, due to the very low free
electrons count per cubic centimeter, that is the yardstick used by
scientists to measure ionization. Maximum useable frequencies at the
peak times are not exceeding more than 25 megaHertz, and then this is
happening for very short periods of time. So, if you happen to pick up
DX signals on frequencies above 25 megaHertz, you can be sure that they
are reaching you via the Sporadic E clouds that are typical of this time
of the year and that have nothing to do with solar activity. Item two:
From time to time the world receives news about a sensational new
antenna system … it happens over and over, only to end up to be yet
another scam to funnel money into the pockets of bandits, or in the best
case, the claims for the ultra miniature antennas with the efficiency of
a huge rhombic or curtain array may come from someone that , although
honest may be absolutely ignorant of electromagnetic wave theory… This
seems to be the case with a Swiss invention, quote , unquote on the word
invention, that goes under the name of the ROOMCAP antenna, whose
inventor claims that the 1.5 meters long piece of metal and a coil is
capable of replacing a full size half wave dipole antenna on the lower
frequency amateur bands. The inventor, again quote, unquote on the word
inventor, refuses to provide information about his antenna, and is
requesting one hundred dollars to be paid to him for a compact disc with
the instructions on how to build his ROOMCAP magic antenna… Recently he
posted yet another message on one of the popular antenna e-mail lists ,
asking list members to visit a web site where he is showing the latest
test of his antenna , something I did at once, only to find that the
antenna test is a comparison between a two wavelengths horizontal loop
and the very short
1.5 meters long ROOMCAP placed on the roof of a small car…
And amigos, that is like comparing apples and oranges, because the Swiss
inventor is ignoring the standard procedure to field
Test HF antennas that calls for installing not one but two reference
antenna systems, a quarter wave vertical monopole over a ground screen
of 120 quarter wave radials, and a vertical half wave dipole, with the
lower branch of the dipole at a quarter wavelength above the ground, and
fed with a transmission line that must leave the center of the elevated
vertical dipole at a 90 degrees angle …
So amigos, be aware that false claims about small HF antenna´s
performance are constantly appearing , especially now that it is so easy
to create a website and fill it with what best could be described as
rubbish…
More radio hobby related items coming up in a few seconds when the mid
week edition of Dxers Unlimited continues in just a few seconds… I am
Arnie Coro in Havana…
………………..
Si amigos, you are listening to Radio Havana Cuba´s Dxers Unlimited
radio hobby program and now here is item three of
today´s program, our technical topics section that will be dealing a bit
more about simple homebrew radios, the ones that you can show with pride
to family and friends while bringing in loud and clear several of the
world´s international broadcast stations.
I remember a few years ago , when a friend visited my shack and left
with a small plastic bag full of electronic components and two circuit
diagrams that I had drawn for him. Two days later he calls me on the
phone and says… Coro, listen to this, and sure, I was able to hear our
own Spanish language program over the phone line… Amigo Carlos then said
that what I was hearing was coming out of the radio he had just
completed to build following the first of the two circuit diagrams he
had taken home . That radio receiver was picking up our 12000 kiloHertz
transmission from the Bauta transmitting center with just a one meter
long wire antenna attached to it. Carlos then told me that the
regeneration control was working very smoothly and that he was able to
pick a popular amateur radio morning round table on 40 meters by
advancing the regeneration control until the single side band signals
were received clearly. Now listen to this: the circuit diagram of that
radio uses just four active devices, draws very little current from the
power supply and can be built into a very small box. The three
transistors used are common NPN type signal devices that Carlos recycled
from a TV set, and the integrated circuit audio amplifier was the LM380
IC I gave him.
Carlos told me that he had wound several coils, and that so far he was
able to pick up stations from the low end of the AM broadcast band up to
the 19 meters or 15 megaHertz international short wave broadcast band.
He then asked about the possibility of switching the coils , so I
started to look into my parts bins to see if I could find a dual pole
three, four or five positions wafer switch, and fortunately my search
was rewarded with the finding of a very nice looking ceramic wafer
switch, two poles and five positions that Carlos has already put to good
use in a second radio he has built…He has left the first experimental
receiver that was mounted on a small piece of half inch plywood, as a
demonstration project to be taken to our next radio club meeting, as
there are many other club members interested in home brewing simple
receivers… Carlos and I talked about the tools that he had used to build
the two radios, and he said all he needed to homebrew the radios where a
30 Watts soldering iron, a set of long nose pliers, a side cutter plier
and a small screwdrivers set, plus his digital multi meter . Carlos
knows how to identify the different electronic components very well, and
he also is good at following a circuit diagram, two very important
elements that are essential requirements if you want to start
homebrewing radios.
Si amigos, yes my friends, oui mes amis, developing your skills to
homebrew radio equipment is one of the 84 ways of enjoying this
wonderful hobby , yours and mine: RADIO…
…..
QSL on the air, YES, QSL on the air to Dxers Unlimited´s listeners that
have requested the Polyakov simple short wave
Receiver circuit diagram… I now have ready here a small text file with
more information about that very simple circuit , that uses just two
signal diodes , a transistor injection oscillator and a two transistors
audio amplifier … Of course amigo Kevin that you can add an integrated
circuit audio amplifier following the two transistors of the receiver´s
audio stage, and that will bring up the set´s volume to room filling
levels… But, you will need more current from the power supply, so the
batteries will last much less than when they are feeding just the three
transistors of the original receiver design. Answering amigo Edward from
the UK, I must emphasize that the Polyakov detector is not your best
option for listening to AM stations , because you must keep the
frequency of the injection oscillator within just a few cycles per
second from the AM station´s carrier frequency or otherwise your audio
will show a sort of growling sound that is very annoying. Do remember
that the Polyakov detector requires that the local injection oscillator
operates at half the receiver´s frequency , something that is very
useful as it is easier to make oscillators more stable when they operate
on lower frequencies. As a matter of factI have used the Polyakov
antiparallel diodes mixer,that by the way is the correct name of the
circuit, to down convert a 2 point two GigaHertz signal to a 144
megaHertz IF, and it worked very well also in this particular
application. When used as a product detector you actually have two main
frequencies at the output, and one of them is, of course, the audio from
the station you want to hear !!!. As compared with a four diode double
balanced product detector, the Polyakov twin antiparallel diodes product
detector has several advantages, and one of them is the fact that the
injection oscillator frequency is operated at half of the signal
frequency…For those of you that have not yet sent a request for the dot
pdf file of the ultra simple 40 meters amateur band Polyakov detector
receiver, let me remind that the e-mail address to send your request to
is inforhc@xxxxxxx, again slowly and using the phonetic alphabet…
inforhc@xxxxxxxxxx It is a very small size computer file that is sent as
an e-mail attachment, as a matter of fact it is only 32 kilobytes of
data so it will be downloaded just after pushing the download key of
your computer.
…………….
Just to complete the information about the easy to homebrew Polyakov
detector receiver for the amateur bands, let me add that a 30 meters
band version requires the use of a five megaHertz variable frequency
oscillator, that at the same time provides an excellent calibration
mark, because you only need to zero beat the five megaHertz injection
oscillator to any time and frequency standard station that uses this
frequency or also 10, 15 and 20 megaHertz. The amateur 30 meters band
starts at 10.1 megaHertz and it is a digital modes only ham band, in
other words you won´t hear any phone stations from 10.1 to 10.150
megaHertz, or at least you should not hear any voice signals there,
although from time to time illegal stations do use that range of
frequencies for their outlaw activities… The ultra simple receiver uses
a one transistor variable frequency injection oscillator, but a more
sophisticated , and of course more complicated version uses a classic
three transistors VFO or variable frequency oscillator, that is made of
a Colpìtts oscillator stage, followed by a two transistors buffer for
optimum isolation. Using a field effect transistor for the oscillator
stage increases both long term stability and makes the circuit less
sensitive to small voltage and temperature variations, because the FET
or field effect transistors are high impedance devices that provide much
better performance than bipolar transistors when used in oscillator
circuits.
…………
ASK ARNIE , si ASK ARNIE, yes ASK ARNIE is the most popular section of
this program, and Dxers Unlimited listeners from all around the world
send their questions that when answered here have made possible for many
other listeners to learn more about radio and solve some practical
problems too. Today´s question sent by Jonathan from Lagos in Nigeria is
typical of type of request I get here every day, Jonathan wants to know
what would be the best amateur band or bands to set up at his soon to be
on the air ham radio station, and he adds, Arnie , of course that I am
looking for your answer regarding the relation between the present phase
of the solar cycles and what may be or may not be worthwhile . Well
amigo Jonathan, the two solar cycles are now in what is the beginning of
an overlap period that may extend for a period even as long as a year,
and solar activity is going to remain within effective sunspot numbers
that won´t go higher than 20 units… Under such circumstances, my advice
is that whatever resources you are going to invest on your ham radio
station, should go to antenna systems from 160 meters to 20 meters, with
perhaps a very simple wire antenna added for operation on the bands from
17 meters to 10 meters. You will find that most of the time , at this
phase of the solar cycles, frequencies above 18 megaHertz will simply
won´t propagate trough the ionosphere… But, from time to time, as for
example during the summer months you may hear some activity on 12 and 10
meters via sporadic E skip…. Amigo Jonathan , if your budget is limited
try installing a 40 meters band half wave dipole as high and as in the
clear as possible, and add to it a pair of twenty meters band elements,
so that you will end up with an effective three bands antenna… The 40
meters band dipole, the 20 meters band dipole that are both half
wavelength resonant antennas and then your 40 meters band antenna will
also perform quite nicely as a three half waves center fed system on the
15 meters band. If you are planning to use , as you explain in your
e-mail a modern high tech solid state transceiver with a built in
automatic antenna tuner, feeding the above mentioned antenna with 50
ohms coaxial cable via a one to one balun will allow you to enjoy
amateur radio during the next two years or so, and allow enough time for
the future installation of a rotatable multiband Yagi antenna that will
provide optimum performance during the peak years of the new solar cycle.
And now as always at the end of the show here is Arnie Coro´s Dxers
Unlimited´s HF plus low band VHF propagation update and forecast… Very
low solar activity, just one sunspot active region in sight, a lot of
sporadic E skip all over the northern hemisphere, including great
double, triple and even four hops propagation events… See you next
Saturday and Sunday UTC days at the weekend edition of the program
amigos… !!!
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