Dxers Unlimited's mid week edition for 23--24 June 2009

By Arnie Coro radio amateur CO2KK Hi amigos radioaficionados around the world and orbiting Planet Earth aboard the ISS... Welcome to the midweek edition of Dxers Unlimited, our station's twice weekly radio hobby program... I am Arnaldo, Arnie , Coro, radio amateur CO2KK and here is now item one of today's program: Two new solar sunspot active regions 1022 the first one to be seen came out almost at the center of the solar disc, so if it develops, its transit will be lasting about one week and not the typical almost two weeks that it takes for a sunspot active region to transit from one end of the solar disc to the other, if it comes into view at the edge of the Sun. Active region 1023 was found by optical observers later...both are cycle 24 spots because of their magnetic polarity...Together the two new sunspot groups have sent the daily solar optical sunspot count to 24... but now as you hear this, group 1022 is rapidly fading away... More information about sunspot cycle 24 and a complete, detailed HF and low band VHF propagation update at the end of the show... Now here is item two, a recent debate regarding the optimum way to stack 2 meters band antennas that are used for FM long distance communications... The 2 meters band FM segments are used to communicate with mobile units and via repeaters to both fixed and mobile stations, so the antennas are vertically polarized. The still in progress debate is about how one should stack two or four Yagi antennas for FM DX and the consensus seems to be in the direction of stacking them vertically because it will reduce the vertical angle and optimize the Take Off Angle, so that more radiated energy will be sent near to the horizon. It is clear now that vertical stacking is the way to go in order to make the Yagi antennas generate a vertical radiation pattern that puts more energy closer to the horizon or in other words to produce a lower Take Off Angle. After looking at how to optimize a pair of 5 element Yagis so that they will radiate more energy nearer to the horizon, it was found out by antenna modeling first and later by actually building the system that the two 5 element Yagi antennas separated by one wavelength from boom to boom will work very nicely and that in the case of the longer 9 element Yagi antennas the optimum low TOA * Take Off Angle * will be generated with a separation of and one and half wavelengths . If the antennas are stacked as a horizontal array, this will narrow the azimuth sector that can be covered, but the all important for DX work vertical radiation main lobe will be the same as for a single Yagi. One additional comment about homebrewing a stack of 2 meter Yagi antennas is that the best approach to keep them well isolated from the tower or mast is to support the antennas with an extension that prolongs behind the reflector element, a standard practice at professional installations on the VHF and UHF and Microwave bands ! Stay tuned for more radio hobby related information, coming to you from Havana, in a few seconds, after a short break, I'll be back with you amigos... ........................ You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited and here is item three: More about antennas for the VHF and UHF amateur bands... answering a recently received question from listener Anthony in Scotland, I must emphasize that it is absolutely true that "real life" results confirm that horizontal polarization of VHF and UHF transmissions reach further than vertically polarized signals. BUT... the fact is that here in Cuba where I live there are almost none 2 meters transceivers that are capable of operating on CW and single side band. Every single Cuban radio amateur that owns a 2 meters band FM rig wants to work DX... that's a fact of life... So, we install the best possible antennas and go ahead using the full potentialities of the FM voice and digital modes, that as everyone knows are several decibels below the so called narrowband modes. Cuban ingenuity has developed alternatives for due to the lack of antenna rotors, two antennas.are installed on the same mast with the typical set up been one omnidirectional antenna and a 5 to 9 elements Yagi. Switching between the two antennas is achieved by a relay located atop the mast or tower. The Yagi is carefully aimed at the highest and farther away repeater ! Another option is to install two 5 or 6 element Yagi antennas, with one aiming e roughly to the West and the other a little South of East, so that optimum coverage of the big and long island of Cuba is achieved. Yes, FM 2 meters band DX is possible... you just keep the squelch open and although results are no match to what can be done using the so called weak signal modes, it is certainly DX, and radio amateurs here enjoy it just as those that have the opportunity of Dxing using CW, SSB and advanced digital modes using PSK31 , WSJT , Olivia etc. In order to be able to connect the two antennas to the same feedline via a relay it is always a good idea to measure an odd number of quarter waves to reach the relay from the antenna, just as you would do with a normal stacking of two antennas . In order to keep it simple, we use the shield of the coax as one side of the power to the relay, and add another wire in parallel with the downlead to feed the + voltage to the relay, instead of using radio frequency chokes and capacitors to isolate the direct current feed to the relay from the radio frequency. We do run DC for the relay and check with a Digital Multimeter how much voltage actually reaches the relay at the top of the mast or tower... then compensate the voltage drop by increasing the voltage of the DC power supply located at the shack. The antenna that works more is connected to the relay's contact that is ON without the DC feed to the relay, and the antenna that you use less often is the one that goes to the other contact. We found out that rather common SPDT and DPDT relays work well in this rather unusual application RF , and NO, they are NOT coaxial relays, so no connectors are involved ... just solder the three braids together, and the center conductors to the terminals of the relay and that's it !!! ......................... You are listening or reading the mid week edition of Dxers Unlimited, here is now item four : Still missing, the long awaited at least medium priced DRM receiver ! So far not a single manufacturer of short wave receivers has brought to the marketplace a radio capable of picking up Digital Radio Mondiale broadcast standard signal. A recent exchange with a senior Cuban University Professor that happens to be not only very well prepared from a theoretical point of view, but that also has lots of practical experience in both telecommunications and broadcasting, led to a clear picture about the future of DRM receivers. The Cuban expert stated that he thought it was possible that in the near future a complex integrated circuit designed to process the different options of DRM broadcasts could lower the production cost of the radios so that they will be competitive with present day short wave analog receivers. Professor Amador also told me about how he and several of his students are receiving several daily DRM short wave broadcasts using a software defined receiver or SDR. According to their monitoring , and as expected, powerful short wave DRM signals provide near FM quality reception, but weaker signals suffer from very annoying sudden cuts, that are very different in nature from the slow fade out and fade in typical of short wave analog broadcasts. By the way, amateur radio operators are using also a form of digital voice transmission that fits into the 3 kiloHertz bandwidth allowed for ham radio voice signals. No doubts amigos, no doubts at all, as soon as not one but several radio manufacturers bring out to the marketplace a medium priced DRM capacble receiver , things will take a turn for the better finally rewarding the efforts of all who have contributed for a long time to create and establish a digital mode for short wave radio broadcasting. .......................... You have questions, and it's always my pleasure to answer them as soon as possible on the air and also directly to your e-mail or postal address... ASK ARNIE is the number one most popular section of this program, and it has helped many listeners around the world to solve technical problems and learn more about HF propagation. Send your radio hobby related questions to inforhc at enet dot cu, again inforhc at enet dot cu, or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana , Cuba. Now here is item five...for those of you faithful listeners that follow Dxers Unlimited's programs, here is more news about the use of recycled electronic components from the energy saving fluorescent light bulbs... All my efforts to make those BUL128A transistors work above the 4 megaHertz frequency range have proven to be a total failure... But, there is still a possibility of making them work on the 40 meters band by using another circuit approach. The BUL128A NPN transistors have proven to work nicely on 160 and 80 meters, and of course that they will also work quite well on the 2200 meters or 136 kiloHertz band. The goal of designing and building an amateur single band transceiver for 160 or 80 meters can be achieved, but it will not be possible in the case of the 40 meters band. In any case, just by adding three NPN transistors that are able to operate properly as linear amplifiers on the seven megaHertz band , we can complete a very low cost, easy to assemble amateur transceiver, with the supply of a large number of its electronic components found at zero cost, just by recycling the electronic fluorescent energy saving lamps and testing all the parts before using them to assemble the new rigs !!! And now amigos as always at the end of the program, here is Arnie Coro's Dxers Unlimited's in the public domain, not copyrighted , for free distribution, HF plus low VHF band propagation update and forecast... This is special for the BLOG , as an update after the show was digitally recorded Tuesday morning. This was uploaded to the BLOG at 0410 UTC Solar activity still at very low levels, but two active sunspot regions in sight have a very important meaning to us, as they are both from cycle 24 , something that can be assured because of the magnetic polarity they are showing. Active region 1022 was slowly fading away, and the optical sunspot count went down from 24 to 12 by late Tuesday. I am receiving many reports of the sporadic E events, that include transatlantic propagation on 10 and 6 meters . Expect a better shaped maximum useable frequency curve that shows a very interesting upward swing just after local sunset. inforhc@enet.cu Via Arnie Coro Blog