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By Arnie Coro
radio amateur CO2KK
Hi amigos radioaficionados all around the world and orbiting Planet Earth ! 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 from 05 to 07 UTC. 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 31 degrees Celsius, and we were enjoying a beautifully blue sky... As a matter of fact, ideal weather to go to the beach !!! But later in the day, about two to three hours after local noon, we are seen big thunderstorms that make radio reception very difficult due to the high level of static crashes, and of course one has to disconnect all radios and other electronic equipment until the thunderstorms are over... Now here is item one: Solar cycle 24 picking up, but not at a very fast speed... nevertheless there is at least one active sunspot region in sight, although it is now slowly loosing steam... More about solar cycle 24 and the HF propagation update and forecast as always at the end of the program... Item two....More about DRM , the Digital Radio Mondiale transmission standard, how it sounds, and what may happen with it in the future ...... Item three: Thanks amigos for the nice e-mail messages received about the recent programs that have included information about radio noise and the problems associated with radio frequency noise generating devices, from table top lamps to aquarium air pumps... not to mention, those big screen Plasma TV sets. Fortunately it seems like many of you actually solved some of your radio noise QRM problems by following some of the ideas I have been giving here on a regular basis... More about radio noise reduction techniques today, when I will answer some of the questions sent in by several listeners... By the way, the INTERNET access distribution system via the power lines , the so called BPL or Broadband over the Power Lines, if implemented may prove to be a nightmare for radio listeners everywhere the system is installed !!! Item four: My four diode voltage quadrupler 4X crystal set continues to amaze visitors to my shack. Some dyed in the wool experimenters tell me that they have never heard 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 HIGH AUDIO VOLTAGE OUTPUT 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 five 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 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 !!! Standby now for a few seconds amigos, the mid week edition of 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 two in detail... Digital Radio Mondiale, DRM technology promised to be a new form of radio broadcsting that what could make possible short wave broadcasts that sounded like a local FM station !!! But, short wave propagation continues to be the stumbling block for DRM... Tests made on the several international short wave broadcast bands are not very satisfactory at all !!! The DRM digital signal, when propagation conditions were very good , made it all the way to the distant location producing an amazingly clear audio , in fact the frequency response can be 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,now let me add that in your's truly humble opinion, the DRM system is not ready yet to take over from standard double side band plus full carrier amplitude modulation broadcasts on short wave ... Something is missing on the DRM technology so far , because it takes only a very little fading for the DRM signal to just vanish, producing a hole in the audio output.... Instead of the slow fade out and fade in typical of analog signals, the DRM signal disappears for periods of from one or two seconds, to even half a minute when there is a very deep fade...so there is still much work to do, among other things , there is the need to develop some form of storage and error correction of signals , so that the annoying cut outs can be eliminated... Last but not least, there is also the need to develop low cost integrated circuit chipsets for DRM radio receivers.... One other element against the expansion and future popularity of DRM is that at present the receiving software is not freeware, and that's something that may prove to be another big stumbling block for the system. DRM test will continue from the United Kingdom, Canada, Bonaire, Portugal, French Guyana and Ecuador and New Zealand , but there very few receivers around the world that are able to pick up those digital transmissions. ........ Si amigos, yes my friends, oui mes amis, you are listening to the mid week edition of Dxers Unlimited and here is our next feature in detail..., Radio noise problems make reception difficult in many parts of the world, and now some new digital broadband 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, especially the so called BPL or Broadband over the Power Lines systems 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 big air spaced variable capacitors, connected to the special voltage quadrupler detector that uses 4 highly sensitive hand picked germanium diodes and four low loss mica capacitors of 2000 picofarads each..also hand picked for perfection . 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, as a matter of fact it is an EXCELLENT AM BROADCAST BAND TUNER !!!!.. If you want to know more about this unique crystal set that doubles as an excellent high quality AM broadcast band tuner, just send an e-mail to inforhc at enet dot 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 our nex item of the midweek edition of Dxers Unlimited.... it took just a few minutes to solder 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...If your supply uses a integrated bridge rectifier, then replace it with four individual diodes and solder the disk ceramic capacitors in parallel with each diode to eliminate the annoying hum !!! 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 very low and will very probably continue at the very low levels for the next three days. The daily sunspot count is 12, and there is just one active sunspot regions that doesn't have enough energy to generate significant solar flares. The Smoothed Sunspot Number or SSN, is around 10, indicating that we are still going to see rather poor daily maximum useable frequencies during the daylight hours... !!! Be on the alert for more really good sporadic E skip openings !!! 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 recently received several nice radio hobby related articles contributed by Dxers Unlimited's listeners that will soon be on the air here !!!
Posted by Arnaldo Coro at 8:10 PM
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