Dxers Unlimited
Dxers Unlimited´s mid week edition for 6-7 May 2008
By Arnie Coro
Radio amateur CO2KK
Hi mis amigos radioaficionados around the world and orbiting the Earth… welcome
to the mid week edition of your favorite radio hobby program , the one and only
covering at one time or another the more than 83 ways you and I share our spare
time enjoying this wonderful hobby :RADIO…
Si amigos, yes my friends, oui mes amis… here at Dxers Unlimited YOU are the
center of everything, and that´s why this program has helped many listeners to
obtain their radio amateur licenses, so that they could then operate their own
ham radio stations… New radio amateurs from the USA, Canada, the UK, France ,
Germany, Japan, New Zealand, Mexico and Brazil among other nations are now
enjoying this wonderful aspect of the radio hobby, after listening for some time
to Dxers Unlimited and becoming then interested in amateur radio. As many of us
did years ago, the newcomers to ham radio started as short wave listeners and
they continue to enjoy picking up short wave broadcast stations from around the
world ! Item two: HF propagation, still in the doldrums, but there are some good
signs of possible improvements in the near future… the emergence of new solar
data that shows without any possible mistake that solar cycle 24 is just
stretching its legs and about to start with more frequent sunspots … Solar
scientists are keeping track of what´s happening 93 million miles away from
Earth by using sophisticated Sun monitoring satellites. One of them under the
acronym of
SOHO, Solar Orbiting Heliospheric Observatory, has now exceeded its theoretical
useful life span, but it is still in such a good shape that scientist believe it
will provide very important information about the now starting up solar cycle…
Item three: As I have said here many times, amateur radio need not be an
expensive hobby at all… It can be enjoyed by people on a shoestring budget, and
let me add that sometimes those of us with limited budgets seem to enjoy it even
more than those who have the opportunity to buy the most sophisticated and
expensive radios and antenna systems… Take for example how just recently a
newcomer to amateur radio needed to complete a ham radio station in order to be
able to obtain his license.
Here in Cuba you must provide the telecommunications authorities with the block
and circuit diagrams of your homebrew transmitters or transceivers, and after
they are approved to comply with the spectrum protection regulations, then the
radio inspector visits your station and performs a test, before the license is
extended. The amateur radio license lasts for a three year period, and it costs
3 cuban pesos and 33 cents per year. Well, back to the new radio amateur, he was
in a hurry to complete his station, he already had a nice professional short
wave receiver, so in order to obtain his license, he only needed to homebrew a
simple transmitter, and here it was when he asked for my help… More about the
ultra simple, minimum parts count CW transmitter than resulted from that request
in a few seconds, when the midweek edition of Dxers Unlimited continues … I am
Arnie Coro, radio amateur CO2KK in Havana…
…..
This is Radio Havana Cuba, and here we are on our 47^th year on the air.
Radio Havana Cuba is has been on the air since 1961, and ever since that first
day broadcast all our frequencies have been legally registered by the Cuban
Ministry of Communications until the year 2000 and from the year 2000 to this
date by the Ministry of Informatics and Communications . Cuba is a member nation
of the International Telecommunications Union and registers the use of all of
its broadcasting frequencies with the ITU according to the established
procedures. And for those ignorant persons that are claiming that membership of
the so called HFCC or High Frequency Coordinating Committee is mandatory, let me
underscore that the HFCC although recognized by the ITU as a voluntary
organization is NOT and I repeat this is NOT in charge of registering the
frequency assignments for international broadcasting for all ITU members. A very
easy to do on line consultation, will show up immediately that not all
ITU member nations form part of the HFCC, and that the nations that are not
members, may register and do register their use of the international short wave
or decametric broadcast band frequencies directly with the ITU in Geneva. As a
matter of fact the ITU Geneva office runs a complete and detailed international
short wave broadcasting compatibility program that is available to all member
nations , so it is in fact available for those that form part of the voluntary
HFCC group and to those that have chosen for one reason or the other to not
become part of the so called HFCC group.
My advise to those who voice out unsubstantiated and wrong opinions about
international short wave broadcasting is to learn more first about the
coordination procedures set up by the ITU before claiming things about the non
membership of nations on the HFCC.
Every broadcasting period, RHC frequencies are properly registered with all the
operating parameters requested by the ITU, and that procedure is carried on with
the proper advance notification by the Cuban Ministry of Informatics and
Communications , that then receives from ITU Geneva the list of how our
frequencies were registered and all the possible incompatibilities with other
administrations frequency registrations, so that they can be worked out in such
a way that better reception of international broadcast stations will result for
the listeners.
……
You are listening to the mid week edition of Dxers Unlimited and here is now our
technical topics section for today… The design, construction and actual on the
air testing of an incredibly simple amateur radio CW transmitter that solved a
very practical problem for a newcomer to the hobby… because after he finished
assembling here at my workshop his ultra simple transmitter and power supply, he
was able to obtain his amateur radio license… As I already explained here at the
start of the program, Cuban radio amateur regulations prescribe that the person
requesting to obtain the license to operate and amateur radio station must show
an actual operating station on the air… The station is then inspected and
approved for operation, and finally the callsign is issued to the new radio
amateur..
So , this new ham, Frank, came in and told me that he had a nice short wave
receiver, but no transmitter, and that he wanted to go on the air as soon as
possible… I told him that I had a 40 meters band quartz crystal, and several
recycled components from broken down energy saver lightbulbs, plus a stock of
other electronic components recovered from old TV sets. He was very enthusiastic
and ready to wire up his power supply and transmitter immediately.
The first step was to draw the block diagram of the power supply and
transmitter… It was clear that we will be using one of the many plentiful
locally TV set vacuum tubes that are very rugged and reliable… The vacuum tube
transmitter required a power supply capable of providing voltage to light up the
filaments o the tube or valve and high voltage for the plate and screen grid of
the tetrode tube that once served as the horizontal output stage of a black and
white TV set.
A power transformer also salvaged from the same black and white TV set provided
all the voltages required, and in less than three hours we had a nice power
supply providing 6.3 volts AC at up to 5 amperes, and approximately plus 300
volts DC at an incredible half an ampere of current… We added a glow discharge
regulator tube to provide plus 150 volts regulated voltage, and then completed
the power supply with a connecting cable that had a wire for the B plus 300
volts, another one for the 150 volts regulated voltage and a wire for the 6.3
volts AC for the filaments, the fourth wire was the common ground. The four
wires ended in a plug that was made from a broken down octal vacuum tube.
The power supply was tested using dummy load resistors, and it worked perfectly
well from the first moment, so fortunately no wiring errors were mad. We used
the nice 1N4007 high voltage silicon rectifiers that were recycled from the
energy savers light bulbs electronics, and the electrolytic capacitors came from
a retired computer power supply… they have a rated capacity of 330 microfarads
at 200 volts DC, that is direct current working voltage, so we simply put two of
them in series to obtain an effective capacitance of 165 microfarads at 400
volts DC operating voltage. To complete the power supply we used a filter choke
also removed from the TV set, as well as a nice on off switch and a fuse holder
. To add some beauty to our power supply we used a bright red LED to show the
presence of high voltage and a green LED to show that the filament was on…For
those of you thinking that 300 volts would not be enough for the transmitter,
let me say that 300 volts at a plate current of 100 milliamperes will yield a 30
Watts input power, that in our ultra simple transmitter circuit will translate
into no less than 10 to 12 Watts output into the antenna system, a power output
that is more than enough to be able to work many stations on the 40 meters band…
………..
After we completed and tested the improvised power supply built from recycled
parts, we started to work on the simply one tube transmitter, but always leaving
enough space to transform it later into an MOPA transmitter later. That is a
Master Oscillator Power Amplifier, as they were known to the old timers… The
single tube transmitter we built so that my friend could obtain his ham radio
station license uses a TV sweep tube and the crystal oscillator in a simple
oscillator circuit, known among the electronic GURUS as an ECO or electron
coupled oscillator… The screen grid acts as the plate of a triode oscillator to
which the quartz crystal is connected, and this improves the stability and makes
the keying of the oscillator much nicer. We decided to use a classic breadboard
layout, and after about three hours, the rig was on the air, bringing in its
first QSO … During the weekend edition of the program I will tell you more about
this ultra simple transmitter and some of the nice DX we worked despite the poor
propagation conditions …
And speaking about propagation, here is a short form HF propagation update and
forecast, solar activity at very low baseline levels, with solar flux around 68
to 70 units and a quiet geomagnetic field. So don´t expect much DX on20 meters
and above during the next several days amigos…
Send you comments about this program to inforhc at enet dot cu or Via Air Mail
to Arnie Coro, Radio Havana Cuba,
Havana, Cuba
