Dxers Unlimited Dxers Unlimited’s mid week edition for 23-24 October 2007 By Arnie Coro Radio Amateur CO2KK
Hi amigos radioaficionados around the world and in space !!! This is the mid week edition of your favorite radio hobby program, Dxers Unlimited … the one and only dealing with practically all aspects of our wonderful way of properly spending part of our spare time: RADIO !!! Here is now item one: Amazing as it may sound, designers continue to produce very simple radios that work quite well… several nice examples have frequently appeared in SPRAT, the British QRP or Low Power Amateur radio club’s magazine.. I’ll describe two of them for you here later into the program. Item two: Dxers Unlimited’s fans continue to enjoy the use of our exclusive and not copyrighted, in the public domain, HF plus low band VHF propagation updates and forecasts, and you are telling me about how useful they are for Dxing… as always , the propagation forecast will be available at the end of the program., Apologies to those who are used to reading the scripts of Dxers Unlimited on several Internet distribution lists… I have had to do some computer hardware work, and in the process, the automated resending of the scripts software somehow was lost… sounds familiar ? Sure, anyone using computers has seen things just vanish without leaving trace , and that’s what happened with the sending of the scripts to several lists …But now after some tweaking, it’s working again. Item four: The 13 meters long wire with a fan type counterpoise antenna, works much better when installed as a sloper, with the sloping angle between 20 and 45 degrees providing the best signals… It is certainly an ideal antenna for portable work, that can also be installed as a standby system at your home QTH. By adding an easy to homebrew loading coil at the lower end of the antenna, it is possible to make it work from 80 meters all the way up to 6 meters. It is fed at the top using 50 ohms coaxial cable with a coax balun, and one counterpoise radial, so you may call this a dual counterpoise antenna system !. Item five: ASK ARNIE, continues to be THE most popular section of the program , closely followed by the HF plus low band VHF propagation forecasts, and at a not too distant third place, I found ARNIE’s WORKSHOP, after receiving several kind complaints from listeners that told me to include Arnie’s workshop more often into the menu… So, I will do it today, as this program is yours amigos !!! Standby now for more radio hobby related information coming to you from Havana with love. I am Arnie Coro, radio amateur CO2KK… …. This is Radio Havana Cuba, the name of the program is Dxers Unlimited, and YES amigos, we do QSL, we do verify reception reports, and with a fast turnaround too.. send your signal reports and comments about our programs to [EMAIL PROTECTED], or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana , Cuba… now, here is item one… SPRAT, the British G QRP Club magazine happens to be a treasure chest of fascinating radio circuits and projects.. each issue of SPRAT is full of very interesting information for the radio hobbyst, and each and every issue of SPRAT brings a lot of valuable radio hobby related information …. Now , a new offer by the G-QRP Club is making available a CD that contains all the issues of SPRAT from number one to number 136, and that amigos is a treasure chest of really valuable radio hobby related information. Three different short wave receiver circuits will be the subject of my comments here today, they are all extremely simple ones. An experimental direct conversion receiver designed by Rudi Burse, radio amateur DK2RS from Konstanz , Germany uses four green light emitting diodes or LED’s for the detector. The GREEN LED receiver simply consists of a tuned circuit for the band you want to receive, link coupled to the antenna, and to the detector that is made using two series connected green LED on each leg of the product detector… The injection oscillator has to deliver 6 volts peak to peak to the detector diodes, and the audio recovered is sent to a standard high gain audio amplifier .Why Rudi used green light emitting diodes for the detector of his direct conversion 80 meters receiver, I can’t tell, but you can be sure that as soon as I finish wiring up and testing mine, you will certainly learn about how it worked in an upcoming edition of this program !!! The other ultra simple receiver published by SPRAT magazine uses the well known POLYAKOV direct conversion circuit. The POLYAKOV detector uses the injection oscillator at half the operating frequency , in this particular case, the VFO uses just one NPN small signal transistor connected to a quartz crystal, operating at half the frequency you want to receive. Oleg Borodin, radio amateur RV3GM from Lipetsk , Russia was the designer of this 20 meter band direct conversion receiver that the G-QRP Club Magazine published. The radio uses two anti-parallel connected silicon diodes for the detector, a single Russian KT315 NPN small signal transistor and the audio amplifier is an LM386 integrated circuit running from a 9 volts battery. I have already scanned both ultra simple receiver circuits, and have them ready for e-mailing them to Dxers Unlimited’s fans around the world that may like to experiment with such simple, yet effective receivers. My own personal experience with the original JAGUEY direct conversion transceiver, designed way back in 1982, is that when used with a well designed front end input circuit, those receivers provide amazing sensitivity, with signals as low as 1 microvolt easily detected… but, they do have one drawback, their selectivity or ability to separated between stations is very poor. The direct conversion radio receivers are used for picking up CW Morse Code Signals , Digital Modes and Single Side Band,but they are not good for receiving AM signals, and can’t pick up FM modulated signals at all. Direct conversion receivers are also known by two other names… SINCHRODYNE and HOMODYNE . in the first case, SYNCHRODYNE comes from the fact that the local oscillator operates at the same frequency of the station that you want to receive, and for that reason the receiver’s output is the audio carried by the station. The exception to this rule is the POLYAKOV synchronous receiver, that uses the local oscillator at half the received frequency. The HOMODYNE name comes from the fact that the direct conversion receiver uses the local oscillator at the same frequency as the one you want to receive… Greek prefix for same, is of course HOMO,so this radios are also known as HOMODYNE receivers !!!And after this complex lexical explanation, let me add something…The original JAGUEY 82 Cuban designed single band amateur transceiver, was tested against a sophisticated and really expensive factory built transceiver… The tests showed that our design was at least as sensitive as the very expensive professional equipment , registering a measured sensitivity of less than one microvolt per meter, producing perfect CW Morse Code copy of such a signal. Adding well engineered audio filtering to a direct conversion receiver can turn it into a really wonderful radio by all standards amigos. NOW, here is my special offer for today: TWO SIMPLE DIRECT CONVERSION RECIEVERS DIAGRAMS and building instructions available to all Dxers Unlimited’s listeners that request them to my e-mail address: send your request for the DIRECT CONVERSION RECEIVERS INFO PACKAGE to [EMAIL PROTECTED], again, [EMAIL PROTECTED], and I will send it to you via e-mail as a graphics attachment. For those of you without e-mail capability, just send a postcard to Arnie Coro, Radio Havana Cuba, Havana, Cuba, and Irma , from our correspondence department will send you a printed version of the circuit diagrams and building instructions !!! Radio is a fun hobby, and believe me amigos, there is nothing more magical than listening to a radio receiver you have just finished building !!! … Si amigos ! Your radio is tuned to Radio Havana Cuba, 46 years on the air at your service. I still remember when our first 10 kiloWatt Swiss built Brown Boveri transmitter went on the air as an experimental station on the 24th of February of 1961…And that was our first high power transmitter, because when we began to operate, we started by using a 1 kiloWatt Gates short wave rig that had a 4-1000A output tetrode, modulated by a pair of 833 triodes. As the steel towers for the antennas had not arrived yet from Switzerland, and we needed to put the station on the air, we made our first two antennas using wooden poles from the local power company !!! Today, at the Bauta transmitting station West of Havana, we have new 100 kW transmitters, that have already replaced the original ones !!! So I am sure that you will be picking up our station in a much better way now !!! Item two: Yes, all tests done here show that the 13 meters long single wire antenna plus end loading coil plus counterpoise works better as a sloper !!! As a matter of fact, I already installed one permanently sloping down from one of my towers at CO2KK. The 13 meters wire sloper is working nicely on the 20 meters band with my 2 Watt QRP or low power transceiver that I enjoy using around 14060 kiloHertz, the international QRP calling frequency… Item three: Short visit to Arnie’s Workshop… that by the way needs a full clean up and organizing to take place as soon as possible !!! At a corner of one of the two workbenches, I am giving the finishing touch to a homebrew antenna tuner…This one is rather unusual because it was designed for portable operation and fits into a very small case. It uses two compact air spaced variable capacitors and a homebrew coil fitted with 15 taps, that will give a very wide range of tuning possibilities… As soon as the project is completed, I will make start testing it with my new QRP multi-band rig, that operates from 160 to 10 meters providing 5 Watts on all modes !!! … You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and amigos, as always at the end of the show,here is our exclusive and not copyrighted HF plus low band VHF propagation update and forecast… Solar activity continues to be extremely low, as we are going trough another extended period of zero sunspots… The slight disturbances are due to coronal mass ejections, not to solar flares. Expect rather nice conditions on the 25 meters band , that is 11.6 to 12.1 megaHertz practically all day long… as it is now the most useful band for international short wave broadcasting , closely followed by 31 meters, spanning from 9.4 to 9.97 megaHertz. For radio amateurs, your best band for Dxing during local evening hours will continue to be 40 meters amigos! No signs of solar activity increasing for the moment, as the winter DX season advances with the lowest sunspot count in the past 11 years !!! See you all at the weekend edition of Dxers Unlimited, and don’t forget to send me your comments about the program, radio hobby related questions and QSL requests to [EMAIL PROTECTED], or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba ---[Start Commercial]--------------------- Preorder your WRTH 2007: http://www.hard-core-dx.com/redirect2.php?id=wrth2007 ---[End Commercial]----------------------- ________________________________________ Hard-Core-DX mailing list [email protected] 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
