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 42nd 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
