|
|
Dxers Unlimited weekend editionsby Prof. Arnaldo Coro Antichradio amateur CO2KKRadio Habana Cuba
Radio Havana Cuba Hi amigos radioaficionados... you are now listening to the mid week
edition of Dxers Unlimited, the one and only radio hobby program that
provides coverage of each and every aspect of this wonderful way of
making very good use of our spare time
I am Arnie Coro, radio amateur CO2KK in Havana, and here is item one
of today's program... The Joy of QRP, yes amigos, the joy and challenge of operating your
amateur radio station running power output levels of less than 5 Watts
is simply fascinating... Monday morning , while testing a newly built radio frequency linear
amplifier module for an ongoing project, I fed it with RF coming from a
crystal controlled oscillator operating on the eighteen megahertz or
seventeen meters amateur band... The linear amplifier module was connected to a G5RV antenna, and a
three by three CQ on CW brought back an immediate reply from a station
in Michigan , USA... The two way contact was completed and I changed to
single side band voice mode, after checking that the peak envelope power
was no higher than 5 Watts. A similar three by three voice CQ brought
back a station from Texas, reporting a very weak but clear signal that
made possible another two way QSO or amateur radio contact. If I could had operated the QRP transmitter using a three or four
elements YAGI antenna, my 5 and 1 Watt signals would had been heard with
much stronger levels at the other end of the QSO's !!! One of the advantages of QRP or low power operation is that your ham
radio station will use very little electricity , making possible to use
batteries , something that becomes quite important during emergencies. Now, here is item two of the midweek edition of Dxers Unlimited Solar scientists are meeting in Egypt to promote research about
upcoming solar storms... It is a well known fact that strong solar storms can knock out power, disable satellites, and scramble Global Positioning System signals making them unusable, so learning about them is something really important due to their impact on Earth. Scientists describe the effects of Solar Storms by saying "These are
global phenomena," that " need to be monitored all around the world." Although space weather is usually associated with events taking place
at our Earth's polar regions-- "Northern Lights" Aurora Borealis and
abnormal HF propagation , it is a fact that our planet's equator can be
just as interesting. For example, there is a phenomenon that happens in Earth's upper
atmosphere called the "equatorial anomaly." It is, essentially, a
fountain of ionization that circles the globe once a day, always keeping
its spout aiming toward the sun. During solar storms, especially the big
ones, the equatorial anomaly can intensify and shape-shift, bending GPS
signals in unexpected ways, disrupting the positioning data received and
also during extreme conditions making normal short wave radio
communications impossible. Stay tuned for more radio hobby information that will follow after a
short break for station ID... I am Arnie Coro , radio amateur CO2KK in
Havana, back with you in a few seconds...
................................ This is Radio Havana Cuba, the name of the show is Dxers Unlimited,
and we are on the air Tuesday and Wednesday UTC days , just after the
half hour newscast of Radio Havana Cuba's English language broadcast.
Here is now item three of this program> Nice feedback from listeners all around the world motivated by the
recent descriptions here of low cost, low parts count and rather easy to
homebrew radios... From a very simple two transistors regenerative receiver for AM
broadcast band reception that still amazes me after more than half a
century of having built the first one, to the most recent version of the
Super Islander solid state 40 meters band transceiver. I have spent quite some time since the weekend edition of Dxers
Unlimited went on the air this past Sunday and Monday UTC days replying
to the many requests for circuit diagrams and information about how to
build those circuits that have proven to work quite well, and that don't
require the use of rare and hard to obtain electronic components. As a matter of fact, during a fast turnaround exchange with a regular
Dxers Unlimited listener to whom I sent the circuit diagram of the
simplest possible version of the Polyakov harmonic detector direct
conversion receiver, it was possible for him to locate the required fast
switching diodes on a discarded Pentium One computer motherboard, where
he also found a 7805 voltage regulator and a large number of ceramic
disc bypass capacitors.. He told me in one of his e-mails... and I quote now Arnie, the coil
forms for the bandpass input filter are two medicines pill bottles, made
of a nice looking plastic, possibly polyethylene, and the dual gang
tuning capacitor came from a discarded AM-FM tuner that had been in
storage for a long time, just waiting to be disassembled for recycling
its parts. Amigo Joe also added that he had already at hand quite a few CFL's or
compact fluorescent light bulbs that had failed... He explained that
each circuit board removed from the CFL's provided a large number of
1N4007 silicon high voltage diodes, two medium power silicon
transistors, two high voltage electrolytic capacitors and many polyester
capacitors capable of handling up to 630 volts DC in some instances. Joe has already completed the Polyakov harmonic detector receiver,
and is listening every evening to the 40 meters amateur band using his
homebrew radio. In yet another e-mail , Joe added that he has already
picked up amateur single sideband stations from the USA, Canada, Italy,
France, the UK and several Caribbean countries. In his comments he adds, and again here I quote Arnie, although the
Polyakov direct conversion receiver does not have any audio filtering,
when there is no QRM, as it often happens now on the 40 meters band
segment betwen 7100 and 7200 kiloHertz, the little two diodes plus one
transistor and one integrated circuit receiver provides amazingly clear
reception of DX signals !!! I even picked up an Australian radio amateur
while he was having a nice two way contact with a station in Florida
just before sunrise my local time here , near Atlanta , Georgia. Now let me add that if the Polyakov direct conversion harmonic
detector receiver's audio output is fed to a pair of audio filters, the
improvement in the quality of reception is really outstanding. One of
the audio filters is sharply tuned to around 700 Hertz or cycles per
second, while the other filter provides a bandpass response between 300
and 2700 Hertz of cycles per second... The filters are built into a separate circuit board, and they can be
switched from the receiver's front panel... I recently run some
comparative, side by side tests, between this more sophisticated version
of the Polyakov direct conversion receiver equipped with audio filters,
and my trusted and reliable Kenwood TS 820-S transceiver, that has an
excellent receiver performance.... Switching back and forth between the
two radios while listening to a very weak signal SSB voice signal on 40
meters, it was quite a rewarding experience to witness the amazing
perfomance of the low parts count and rather simple Polyakov receiver...
Of course that it was no match for the Kenwood TS 820's reception, but
it came quite close... Sure amigos, you won't need to spend a lot of money in order to enjoy
the thrills of amateur radio communications
The Polyakov harmonic
detector receiver , with the two audio filters , and possibly with a
single additional transistor RF amplifier can be built using common
tools and what is still more important , using electronic components
that are readily available by recycling old equipment that otherwise may
be going to the trash
My latest Demonstration Version of the
Polyakov receiver includes also a simple easy to build power supply
that uses a Wal Wart transformer and a handful of parts to provide well
regulated 9 to 12 volts DC to the radio, that also can be powered for
many , many hours of nice reception using eight nickel metal hydride
size AA rechargeable batteries. And now as always at the end of the program, when I am here in
Havana, our regular feature, Arnie Coro's Dxers Unlimited's HF plus low
band VHF propagation update and forecast... Solar flux around 85 units,
and the Catania Astrophysical Observatory WOLF number was 45 on Tuesday,
lower than the 66 registered on Monday. Expect nice daytime band
openings on the bands between 14 and 22 megaHertz, and at night the
maximum useable frequency will drop very fast just after sunset
Hope
to have you all listening to the weekend edition of the program next
Sunday and Monday UTC days amigos... Send your signal reports , comments
about the show and circuit diagrams requests to inforhc at enet dot cu
or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba |
