Dxers Unlimited
Dxers Unlimited's mid week edition for 18-19 February 2003
By Arnie Coro
radio amateur CO2KK

Hi amigos ! Welcome to the radio aficionados favorite show... YES, this is Dxers Unlimited's mid week edition, coming to you from Havana, via shortwave, and via the world wide web streaming audio from . Item one VERY , VERY LOW solar activity surprises scientists, as the number of sunspots went down to just 16, yes , you heard it right, optical solar observations made Monday showed no more than 16 sunspots, and a rather easy to spot coronal hole located at a geoeffective position.... Item two: The very low solar activity will make AM medium wave broadcast band DX to be much better IF the effects of the solar wind subside... Item three: A very easy to make antenna for the AM broadcast band Dxer uses a very popular shielded pairs cable that is used for wiring up computer networks... Item four: Radio amateurs around the world are looking at the upcoming WARC 2003 Conference to take place in June, where an attempt will be made to re-align the 7 megaHertz or 40 meter ham band so that all three ITU regions will have the same frequency range. Item five: A very easy to build two transistor oscillator will allow you to test quartz crystals, and will also serve as a very useful injection frequency oscillator for simple frequency converters... Item six: A visit to Arnie's workshop... to take a look at the workbench ... Then item seven will be our popular you have questions and Arnie tries to answer them section of Dxers Unlimited, and at the end of the show, as always, la numero uno, the most popular section of the show, Arnie Coro's HF plus 6 meters propagation upate and forecast... Stay tuned for more radio hobby related information coming to you from Havana. Margarita Delgado is my sound engineer and producer , I am Arnie Coro , radio amateur CO2KK, back with you in a few seconds..

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You are listening to Radio Havana Cuba, and here is item three in detail: One of the most popular computer networking shielded twisted pairs cable can be used to make a simple, yet highly effective antenna for the medium wave broadcast band. A rather short length of the three twisted shielded pairs when connected to make several turns, will provide you with an excellent , highly efficient antenna. In actual practice the six wires that form the three shielded pairs are wired up to produce a six turns untuned loop, yes, you heard it right, it is an UNTUNED LOOP, so it will work quite well on any frequency from about 200 kiloHertz, all the way up to about six megaHertz.... The loop is connected to your radio using a length of 50 ohm or 75 ohm coaxial cable. You can see the loop, and how to interconnect the three shielded pairs to make the six turn loop in a nice computer graphic file... And once again, you can send for it via e-mail amigos !!!! Send your request for the html file showing how to build your own six turn shielded untuned loop antenna to arnie@rhc.cu , again, arnie@rhc.cu. or VIA AIR MAIL send a postcard to Arnie Coro, Radio Havana Cuba, Havana , Cuba...

By the way, the extremely low solar activity that we are seeing right now will produce some very interesting AM medium wave broadcast band propagation conditions !!!

Now here is item four: Its going to happen in June, the world's topmost radio regulations experts will get together in Geneva, Switzerland for a period lasting four weeks, to participate in the World Administrative Radio Conference 2003, where among other topics , an attempt will be made to expand the 40 meters amateur band so that Regions I and III of the ITU will obtain a wider band , compatible with the already existing 300 kiloHertz band available to Region II users... The 40 meters amateur band is extremely useful for short and medium range communications during the local daytime hours, and is also capable of providing worldwide contacts between areas of the world that are in darkness or very near sunset and sunrise !!! Let's hope that the very popular amateur radio assignment is finally made compatible at a world wide scale !!!

This is Dxers Unlimited's mid week edition and here is item five of today's program... two very common, standard NPN silicon transistors , six small carbon resistors, and three capacitors, plus a crystal socket are all the parts required to make a very useful crystal controlled oscillator that will serve not only as a test oscillator, but also may be used as a very easy to make injection oscillator for a receiving converter or even for a transverter. The circuit has enough feedback applied to make even very sluggish crystals oscillate, and it is one of my standard building blocks that make designing new equipment a much easier task.

I have similar building blocks for power supplies, audio amplifiers, RF and IF amplifiers etc.

The two transistor easy to build and easy starting oscillator circuit diagram is also available by sending an e-mail to arnie@rhc.cu amigos, or you can send a postcard to Arnie Coro, Radio Havana Cuba, Havana , Cuba.... You can test all those recycled computer cards and motherboard's quartz crystals using this simple circuit, and I even use one as a frequency standard for my REGENERODYNE receiver, as it generates a precise marker signal every one megaHertz. The building block approach to homebrewing radio gear is a very sound one, as you work starting not from scratch, but from already proven, fully tested, reliable circuits.

For example, if you combine this two NPN transistors quartz crystal oscillator, my cascode RF amplifier module, and my broadband double balanced mixer module , you will end up with a very nice HF converter, that will effectively turn even a very modest short wave receiver into a much more efficient and sensitive double conversion radio !!!!

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Amigos you are listening to Radio Havana Cuba, and in just a few days we will be celebrating the 42^nd anniversary of the day when we started our test transmissions from our Bauta site , way back in 1961... I still remember how our first half wave dipole antenna for the six megahertz band went up between two power utility poles, and matched perfectly to the one kilowatt transmitter, after our chief antenna engineer Jose Antonio Valladares, showed us how to tune a dipole to minimum standing wave ratio by means of a quarter wave stub section of 350 ohms transmission line... A few days later, we had on the air our first 10 kilowatt Brown Boveri transmitter from the temporary facilities that the construction workers had built, and then we started to use our 11760 kiloHertz frequency, that we have always kept on the air ever since !!! Now here is item six: Let't take a glance at my workshop, where a SONY ICF7600 D digital radio is now undergoing a major overhaul, after many years of excellent service... The receiver now is working again, after changing two electrolytic capacitors, but I still how to find out why the volume control simply refuses to work, as the radio is turned on, and I get a constant audio level, that the volume control potentiometer simply can not change.... BIG PROBLEM, I don't have the circuit diagram of the microprocessor controlled digital receiver.... so the repair job will take much longer than expected... Anyway, as usual, I found out that electrolytic capacitors had failed, so now I am going to change them all.... as that's the best approach when dealing with older equipment... Just replace the electrolytics and the tantalum capacitors after about 10 to 15 years of service, and you will always be on the safe side amigos !!! The old SONY ICF7600D did required a lot of cleaning and the removal of dust that had accumulated all along its lifespan, as the receiver was used as a field portable most of the time.It is a nice little radio, with single side band and CW reception capabilities, and although its selectivity or ability to separate between stations is not that great, it has proven to be an excellent standby radio during the hurricane emergencies here, as it can be powered from any six volts DC source.

And another piece of equipment here at the workshop waiting to be repaired is also a receiver, this one is an R403 short wave radio covering from 1.5 to 25 megaHertz , made way back in 1963 in the People's Republic of China. Its an all vacuum tube radio, and after so many years of service its power supply filter capacitors are like new... If you want to know why, here is the answer, they are not electrolytics, they are OIL FILLED PAPER CAPACITORS in hermetically sealed cans... I desoldered them from the circuit, and measured their capacitance and their dielectric loss, only to be amazed about how good they still are... I even measured the ESR or Equivalent Series Resistance, to confirm that those oil filled capacitors will last a lifetime... By the way, the nice radio is not working due to the possible failure of a plate or screen grid bypass capacitor that is shorting the B plus bus to ground ... I hope to have it back in service tonight, as finding a shorted bypass capacitor is not all that difficult !!!

SI, you have many radio hobby related questions, and I always try to answer them as soon as they come in to arnie@rhc.cu or via AIRMAIL to Arnie Coro , Radio Havana Cuba, Havana , Cuba. Today's question is related to the voltage rating of silicon rectifiers, and it there is any easy to remember rule of thumb when selecting them for the maximum peak reverse voltage required for a particular power supply voltage... Well amigo Dieter from Dresden, Germany, YES, there is a very easy to remember rule of thumb.... first of all use the modern avalanche type silicon diode rectifiers, and second, rate them to no less than three times the voltage of the power transformer secondary... for example, a transformer delivering 250 volts AC full secondary voltage to a diode bridge rectifier, will require that the diodes be rated at no less than 750 volts peak reverse voltage, and if you want to be on the safe side, then use one kilovolt rated diodes !!!

And now amigos as always, at the end of the show our exclusive , not copyrighted in the public domain , HF plus 6 meters propagation update and forecast... Extremely low number of sunspots seen yesterday and again today... the daily optical sunspot count was as low as 15 and that's a record low for this solar cycle amigos... It is now an almost spotless Sun what solar observers are watching. The solar flux is moving down, and the effective sunspot number is around 60 and also going down. Planet Earth is affected by a high speed solar wind coming from a geoeffective coronal hole, and that will continue to disrupt the geomagnetic field at higher latitudes.. As the effects of the coronal hole subside, we will very probably witness the best AM medium wave band DX conditions of the past 7 years amigos, so be ready to catch those nice DX signals reaching your radios from 520 all the way up to 1700 kiloHertz !!! Expect much lower daytime maximum useable frequencies during the next five to seven days also... See you at the weekend edition of the program my friends, that's next Saturday and Sunday UTC days ... AND DONT FORGET to send your signal reports, radio hobby related questions and comments about the program directly to arnie@rhc.cu , or VIA AIRMAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba

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

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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 !!!

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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 !!!

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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 !!!