Dxers Unlimited

Dxers Unlimited's mid week edition for 11-12 February 2003

By Arnie Coro

radio amateur CO2KK

Hi amigos radioaficionados ! Welcome to the mid week edition of Dxers Unlimited, coming to you from
Havana, via short wave and also via the world wide web audio feed. I am Arnie Coro, radio amateur
CO2KK, your friend here in the sunny capital city of Cuba where the temperature at noon Tuesday was
about 25 degrees Celsius, and we were enjoying a beautifully blue sky... As a matter of fact, ideal
weather to go to the beach !!! Now here is item one: I'm back home now after a trip to South Africa,
where I saw the practical demonstration of the DRM, Digital Radio Mondiale broadcasting system in
what was one of its first public appearances in front of a group of radio engineers from some 30
countries.

More about DRM , how it sounds, and what may happen with it in the future later... Item two: Thanks
amigos for the nice e-mail messages received about the program that was devoted to radio noise, a
show I had taped in advance of my eleven day trip to Africa. Seems like many of you actually solved
some of your radio noise QRM problems by following some of the ideas I gave on that special edition
of Dxers Unlimited... More about radio noise reduction techniques today, when I will answer some of
the questions sent in by several listeners... By the way, the new INTERNET access distribution
system via the power lines , if implemented may prove to be a nightmare for radio listeners
everywhere the system is installed !!! Item three: My four diode voltage quadrupler crystal set
continues to amaze visitors to my shack. Some dyed in the wool experimenters tell me that they have
never head a crystal radio producing such a loud sound level into the 2000 ohm headphones, and I
even have one version that feeds a high efficiency audio transformer, with a very good high quality
low loss

iron core, and four thousand ohm impedance of the primary , and a tapped secondary to which you can
connect low impedance headphones, like the ones used for stereo HI FI listening... The SUPER VOLTAGE
QUADRUPLER CRYSTAL SET can be built on top of your kitchen table in just a few hours, and it does
not, I repeat this, it does not use any hard to find electronic components... It's a nice weekend
project amigos !!! Item four of today's mid week edition of Dxers Unlimited will be a visit to my
workshop, to talk about a power supply problem that is often present with many radios that are
powered from an external supply... As you will learn, adding just a few electronic components will
clean the supply and make your reception a lot better... AND as ALWAYS when I am here in Havana, at
the end of the program , have your tape recorder ready for Arnie Coro's Dxers Unlimited's HF plus 6
meters propagation update and forecast , a practical guide for optimizing the enjoyment of your
radio hobby , be it short wave listening or amateur radio, or both !!!

Margarita Delgado is my sound engineer and producer, and soon she is going to be very happy because
we are installing a beautiful new sound mixer board and some other studio equipment for her to
enjoy... Standby now for a few seconds, Dxers Unlimited continues after this short musical interval

.......

This is Radio Havana Cuba, broadcasting in English to the world... I am Arnie Coro and here is item
one in detail... Johannesburg , South Africa was the venue for a radio conference where I had the
opportunity to hear the tests of the DRM system DIGITAL RADIO MONDIALE, a very promising modulation
technology that may prove to be what will make possible short wave broadcasts that sound like a
local FM station !!! The tests were made on the little used 11 meter band, on the frequency of
25.800 kiloHertz, and anyone listening to that channel would only pick up what apparently sounded
like computer noise, as in effect it was a digital signal. The transmitter was located at the Sines,
Portugal , site of Deutsche Welle, the German international broadcast station, , running a 250
kilowatt transmitter , that when operating on the digital mode should had produced a output of about
45 kilowatts or so. NOW look at a map, and see the distance between Portugal and South Africa... a
747 leaving Lisbon will land in Johannesburg about 10 hours later !!! But the DRM digital signal
made it all the way to the distant location producing an amazingly clear audio , in fact the
frequency response was much better than the one you can normally expect from the 4.5 kiloHertz
bandwidth that short wave stations normally put on the air. BUT, let me add that in your's truly
humble opinion, the DRM system is not ready yet ... there is still much work to do, among other
things , there is the need to develop the integrated circuit chipset for DRM radio receivers....
because so far , until now, all the receiving tests are done using a receiver with a special adapter
connected to a laptop computer that is equipped with a special software to decode the DRM, Digital
Radio Mondiale short wave broadcasts. This receiving software is not freeware, and that's something
that may prove to be another big stumbling block for the popularity of the system. So now you know
that the DRM tests from Portugal to South Africa were successful, and that the engineers used a
computer sound card with a special proprietary software to decode the signal and play it back trough
a pair of loudspeakers... I am sure that during the coming months, tests will continue , especially
during the upcoming World Administrative Radio Conference that will take place in Geneva ,
Switzerland, during the month of June... Tests will continue from the United Kingdom, Canada,
Bonaire and Sines, but reception will only be possible for those that buy the rather expensive
software and the special decoders, or build their own adapters !!!

........

Si amigos, yes my friends, oui mes amis, 9820 kiloHertz from Havana is back on the air after some
transmitter problems that we had in my absence... So try 9820 kiloHertz with our Spanish language
one hour broadcast from 00 to 01 UTC and then from 01 to 07 UTC in English, now here is item two,
radio noise problems make reception difficult in many parts of the world, and now some new digital
signal distribution systems promise to make reception still more difficult ... According to a recent
survey, the gradual phasing out of computer cathode ray tube monitors and the use of much higher
processor frequencies is certainly going to help computer generated noise that interferes with radio
reception. So , if you have the resources amigos, YES, its true, changing your desk top computer
display to the flat panel non cathode ray tube solid state screen will reduce the radio noise
dramatically.... and higher CPU clock frequencies will also help to keep the HF spectrum cleaner
too... BUT, beware of some of the newer ways of distributing the INTERNET, as some of them are
really a big threat to radio reception !!!

.....

CUATRO, yes QUATTRO, FOUR DIODES connected in a voltage quadrupler circuit provide outstanding
reception of AM broadcast band signals on my ULTRA SENSITIVE crystal radio set that continues to
amaze visitors to my shack... YES, it uses two large diameter , high Q homebrew coils, and two air
spaced variable capacitors, connected to the special voltage quadrupler detector that uses 4 highly
sensitive germanium diodes and four low loss mica capacitors of 2000 picofarads each... The output
of the detector is coupled to a pair of high impedance headphones , the radio's input link is
connected to an external antenna and as usual with crystal sets, connecting an external ground also
helps to boost reception.

But the fact is that here in Havana, even without a ground connection, the radio picks up stations
not only from Cuba, but also from Mexico, Colombia, and the USA during the local evening hours ,
when DX propagation on the AM medium wave broadcast band is possible !!!... Connecting a high
quality low loss audio output transformer with a primary winding of between 3000 and 5000 ohms, will
let you match the VOLTAGE QUADRUPLER RADIO to low impedance headphones, but there is going to be ,
as expected a slight loss , due to the presence of the audio transformer.....I use two tuned
circuits, in order to increase the selectivity of the receiver, and connecting the low impedance 600
ohm output from the transformer to the HI FI audio system brings in very high quality AM reception
!!!

If you want to know more about this unique crystal set that doubles as an excellent high quality AM
tuner, just send an e-mail to arnie@rhc.cu, and I will send you the text describing the circuit in
detail and a small .jpg graphic file with the schematic diagram...

.....

Now here is item four of the midweek edition of Dxers Unlimited.... it took just a few minutes and
just soldering 4 small disk ceramic capacitors in parallel with each of the power supply's diode
rectifier... and the hum that was making reception so uncomfortable just vanished... As a matter of
fact, that's something I do to each and every power supply built at my workshop... each diode is
always wired in parallel with a disk ceramic capacitor of between 5000 and 10000 picofarads, that is
from.005 to .01 microfarads ..., its really a very simple

modification for any power supply, and the results are really amazing, reducing the hum modulation
problems to practically zero...

And now amigos, as always, at the end of the show, here is our exclusive and not copyrighted in the
public domain, free to all people who enjoy this nice hobby... Arnie Coro's Dxers Unlimited's
propagation update and forecast... Solar activity is LOW, and will very probably continue at the LOW
level for the next three days. The daily sunspot count is around 160, and there are no active
sunspot regions that may have enough energy to generate significant solar flares. The Smoothed
Sunspot Number or SSN, is around 90, indicating that we are still going to see rather nice and high
maximum useable frequencies during the daylight hours... The spring equinox for the northern
hemisphere is still about five weeks away, but soon we will start to feel the transition from winter
to equinoctial propagation conditions, and the daytime frequencies available for the longer paths
are going to be higher, while at the same time the nighttime frequencies will certainly move up as
solar illumination of the northern hemisphere and the southern hemisphere start to balance !!! See
you all at the weekend edition of the program and don't forget to take a little time to send me your
valuable comments and opinions about the program, and even if you want to write something for the
show, just go ahead and do it... I have now several nice articles contributed by Dxers Unlimited's
listeners that will soon be on the air here !!!