Radio Havana Cuba Dxers Unlimited
Dxers Unlimited's weekend edition for 20-21 October 2007 By Arnie Coro radio amateur CO2KK Hi amigos radioaficionados around the world and orbiting the Earth. This is the weekend edition of your favorite radio hobby program, the one and only covering all , each and every aspect, of our wonderful hobby.... from short wave listening as you are doing right now, to exploring the deep far space with a homebrew radiotelescope... from giving the finishing touches to a new receiver assembled from one the excellent kits available, to experimenting with a new antenna concept like the spiral loaded dipoles that are now becoming quite popular among radio amateurs that live in very tight quarters... Si amigos, yes my friends... there are more than 81 ways in my list, 81 plus ways of enjoying our wonderful hobby : RADIO... And here is now a nice example... as quartz crystal manufacturing techniques have developed at a fast pace during the past decade, the cost of crystals cut for some specific frequencies used by the computer industry has gone down dramatically... so now, it is not too difficult to assemble your own quartz crystal bandpass filter, an essential component of any receiver or transceiver that is going to be used for serious amateur radio work. Recently I learned about the availability of certain specific frequencies , that are particulary good for homebrewing the bandpass crystal filters, that can be designed to provide the bandwidth required for operating on different transmission modes. So now not only the once popular color burst frequency crystals of 3579 and 4433 kiloHertz used by the NTSC and PAL color TV systems are available to the experimenter... the new computer clock frequencies crystals are more plentiful and cheaper... But there is still another use for those computer crystals, and that is using them to provide the injection frequency for front end converters used ahead of regenerative receivers, turning them into a type of radio known as a REGENERODYNE... More about the low cost computer crystals and how they can be used for making filters and front end converters crystal oscillators in a few seconds, after a short break for our station ID. I am Arnie Coro, radio amateur CO2KK and as always it is my pleasure to share with you about seventeen to eighteen minutes of on the air, on the web and on the Hispasat satellite tiem amigos... stay tuned.. ........ This is Radio Havana Cuba, the name of the show is Dxers Unlimited and yes, we do QSL, we do verify reception reports with a nice QSL card.... send your signal reports and comments about our programs to [EMAIL PROTECTED], or VIA AIR MAIL to Arnie Coro , Radio Havana Cuba, Havana, Cuba. Low cost mass produced computer quartz crystals are making possible that radio experimenters homebrew some really excellent crystal filters. A recent example was brought to my attention my amigo Colbert , who lives near London's Gatwick International Airport. He sent me the circuit diagrams of several crystal ladder type filters that he has experimented with. The simplest one of them all used three 6000 kiloHertz crystals that he carefully matched using a friends digital frequency meter. Colbert explains in his e-mail that he obtained information about ladder type crystals filters from several different sources, and decided to experiment with them. He has done a lot of experiments, and one of the most interesting ones is a variable bandwidth ladder filter that he will be using in a new project, an amateur radio transceiver for the 20 meters band that he is now planning. Colbert has built a six crystals ladder filter that according to him works exactly as it should... He says in his e-mail : Arnie, the professional engineering literature calls those ladder filters by the name of " Assymetrical lower sideband ladder crystal ladder filter" and I fully agree with the authors of the paper , because when the six crystals filters was tested with professional laboratory equipment, the shape of the frequency response curve as assymetrical and favoring the lower sideband, exactly as the authors of the research paper had stated . The most important thing about these filters is that those computer crystals are becoming cheaper and cheaper, so if you do have a lot of patience, the crystals can be tested and their poles and zeros of resonance plotted... Then with that precise information at hand the design of ladder filters is not too difficult. Well amigos, as you have realized, Colbert has gained a lot of experience about crystal ladder filters and his results are very consistent... A high quality bandpass crystal filter can be bought , but they are not cheap, and besides that, if you homebrew your own filter, you learn a lot more about radio and electronics, and that's part of the enjoyment of the hobby too... ....... ASK ARNIE, si amigos, ASK ARNIE, is the most popular section of Dxers Unlimited... it is la numero uno, the number one favorite of our worldwide audience, because as listener Gary from Florida in the USA writes, by listening to or reading the scripts of Dxers Unlimited, you can learn a lot of interesting things about radio... Today's question also came from Florida, listener Stewart from Clearwater wants to know what should the frequency response of a bandpass filter should be so that the best possible quality AM broadcast band reception is achieved. Well amigo Stew, this is a tough question, a difficult one indeed, because one needs to understand that AM broadcast stations transmit on 10 or 9 kilohertz bandwith channels, depending on what part of the world they are located... That means that at either side of the carrier, the audio bandwidth is limited to 5 or 4.5 kiloHertz, depending on the part of the world where you are located. According to highly qualified engineers, the ideal AM broadcast band receiver filter for listening in the Americas, that is ITU Region II should have a bandwidth of SIX KILOHERTZ.... and a very abrupt shape factor between the minus six dB and the minus sixty dB points of the filter's response curve. Listening trough such a six kiloHertz bandwidth filter will make it mandatory to tune the station so that the minus 6 dB point of the response curve falls about 500 Hertz to one side of the carrier,and then your radio will be picking up the full carrier plus one of the sidebands, something that is very good, because you won't have any distortion caused by selective fading. Your sharp cutoff filter will cancel one of the sidebands, and because an AM signal transmits two identical sidebands, your receiver will produce a high quality audio. So amigo Stew, again, look for a SIX kiloHertz bandwidth filter if you want to listen to AM broadcast band stations with good quality and without the bad effects of selective fading distortion. But, if you want to hunt for real DX on the AM band or for that matter in the Long Wave AM band , then my advice is to add a second filter to your receiver, that will provide you with a 2.4 or 2.7 kiloHertz bandwidth... Such a narrow filter is used by practically all Dxers involved in AM broadcast band activities for a very good reason, and that is the fact that it can dramatically reduce the adjacent channel interference that many times makes it impossible to obtain a clear ID of a DX station whose operating frequency is right next to a local or semi local station... AM broadcast band and Long Wave broadcast band DXing are two of the favorite ways of enjoying our wonderful hobby amigos, and you can log many DX stations using low cost receivers too... But, as expected, better radios will bring in many more DX stations , of course ! ...... And now let's move to our next item of today's weekend edition of Dxers Unlimited... getting ready for the upcoming ham radio contest season... Radio amateur operators around the world are now getting ready for what is going to be a really challenging contest season. The extremely low solar activity will make contest operations really difficult, and long standing contest teams are looking for special advice from HF propagation experts in order to optimize their operations so as to make as many contacts as possible under the expected very poor band conditions. As one of our local contest enthusiasts told me last week, the time windows to areas of the world with high participation are going to be of very duration, so in order to have good chances to place among the first in any contest, very accurate propagation forecasts are essential in order to make the best possible use of the very short time windows that are expected during the next several months due to the extremely low solar activity... Having a propagation guru at hand during the contest will certainly make a lot of difference amigos !!! And talking about HF propagation, having access to the on line data of the world's network of ionospheric vertical incidence sounders will make possible to produce very accurate short term forecasts, the ones that are required by contest operators. ...... This is the weekend edition of Dxers Unlimited and now our next item... a quick visit to Arnie's workshop... share with me a couple of minutes testing my new assymetric pulses battery charger that has already revived several nickel cadmium rechargeable batteries that I had thought could not be recharged any longer. Apparently the assymetric pulses produced by the new battery charger design removes bad areas of the plates and brings the cell back to its full capacity. The circuit is not very complicated, but of course that it is not as simple as the typical constant current charger built around an integrated circuit voltage regulator device....Batteries continue to be a weak spot of the radio and electronics industry, and although many new concepts are now in the experimental stages, like is the case of the newer versions of the lithium based batteries , there is still need for more basic and applied research to be done in order to increase the overall efficiency of these sources of electricity essential for the operation of so many of today's electronic equipment. And now amigos , as always at the end of the program, here is Arnie Coro's Dxers Unlimited's HF plus low band VHF 30 to 60 megaHertz propagation update and forecast... Solar activity has stayed at extremely low levels with the solar flux not even reaching 70 units, while the optical sunspot count has been just one zero after the other. On Thursday the Planetary A index showed a marked increase ... ---[Start Commercial]--------------------- Preorder your WRTH 2007: http://www.hard-core-dx.com/redirect2.php?id=wrth2007 ---[End Commercial]----------------------- ________________________________________ Hard-Core-DX mailing list Hard-Core-DX@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/hard-core-dx http://www.hard-core-dx.com/ _______________________________________________ THE INFORMATION IN THIS ARTICLE IS FREE. It may be copied, distributed and/or modified under the conditions set down in the Design Science License published by Michael Stutz at http://www.gnu.org/licenses/dsl.html
