DXERS UNLIMITED Dxers Unlimited’s weekend edition for July 14-15 2007 By Arnie Coro radio amateur CO2KK
Hi amigos radioaficionados around the world and also those of you now in space orbit around the Earth … I am Arnie Coro, your host here at Radio Havana Cuba’s twice weekly radio hobby program… It’s certainly nice to have you listening to the show, and I hope you enjoy every minute of it…Your comments and ideas on how to make Dxers Unlimited a better program are most welcome at my direct e-mail address : [EMAIL PROTECTED] Now here is item one, very low solar activity continues … Sporadic E propagation reports continue to come in from North America, Central America and the Caribbean, as well as from Africa and Europe. Recently received e mail messages talk about excellent VHF bands openings, and one particular recent opening that took place on the 6th of July, reaching maximum useable frequencies up to the 1.25 meters or 222 megaHertz amateur band, that made them lots of VHF operators very happy indeed, as this was their first ever opening on 222 megaHertz, and for some other newcomers to VHF Dxing, their first two meters band opening via the ionosphere … The extremely high free electron density at the height of the sporadic E layer also made possible TV DX signals on NTSC channels 7 to 13 , that operate from 174 to 216 megaHertz. Sporadic E openings are expected to continue during the next several days, and some of them maybe happening even during the late evening hours.. I do insist that there seems to be some sort of relation between periods of very low solar activity and sporadic E events !!! Item two today, will be our Technical Topics section, then item three time slot is for ASK ARNIE, and the pending visit to my workshop will be the fourth item of this program that will come to an end with our exclusive and not copyrighted , in the public domain HF plus low band VHF 30 to 60 megaHertz propagation update and forecast. I am Arnie Coro, radio amateur CO2KK, your friend in sunny Havana, together with my sound engineer and producer Jose Costa Pupo, both of us ready to continue providing you with the most up to date radio hobby related information, as the weekend edition of Dxers Unlimited continues in a few seconds.. ;;;;;;; Si amigos, your radio is tuned to one of Radio Havana Cuba’s English language broadcast frequencies, this is Dxers Unlimited, our twice weekly radio hobby program, and here is our TECHNICAL TOPICS section of the show.The cascode regenerative detector circuit presented here at our mid week edition brought a lot of e-mail requests for the 40 kilobytes file in dot jpg format that shows the schematic circuit diagram of Udo Peter’s unusual radio receiver… Several listeners have asked for more details of this circuit, so here they are/// in the first place, be aware that the cascode regenerative detector was built using a dual triode vacuum tube, of which there are many types that can will perform nicely in this circuit, but, if you don’t have a dual triode in the same glass envelope, just use two identical triodes,and the circuit will work quite well also. Among the triodes tested here in my prototype are the 12AT7 or ECC81 ,that has proven to be an excellent performer, the 12AU7 or ECC82 that showed somewhat less gain as the frequency to which the radio was tuned went up but worked very well up to around 15 megahertz or so, as a 12AU7 according to the vacuum tube manuals is nothing but two 6C4 triodes packed inside the same glass envelope, and also tried out the ECC85, of which I don’t remember its American standards designation, and that proved to be the best performer, providing excellent sensitivity on the 27 megaHertzs Citizens band, a frequency range that is usually very active when sporadic E propagation events are in progress. I was able to pick up lots of Citizens Band skip signals on AM, and even some of the many so called OUTBANDERS, that operate between the top end of the Citizens band and the beginning of the 10 meter band, that is from about 27.4 to 28 megaHertz… Another interesting finding when experimenting with the cascode detector regenerative receiver was that changing the values of the first triode’s grid resistor and capacitor had a significant effect on the performance of the radio !!! Using typical values for classic regeneratives, like 100 picofarads and 1 megaohm , provided inferior performance, and the radio’s sensitivity and selectivity improved considerable when the value of those two components was changed to 22 picofarads for the capacitor and 10 megaohms for the resistor… My advice is that you aim at using the highest possible quality component for that capacitor, because there is no doubt that it is vital element of the circuit. The other component I talked about during the midweek edition of Dxers Unlimited, was the regeneration control potentiometer, and again, let me insist in the fact that it is extremely important to use a very high quality potentiometer , in order to obtain a velvet smooth control of the regeneration that is free of any noise generated by the wiper of the potentiometer…. So amigos, there you are again, learning about a unique radio receiver circuit, the cascode regenerative detector, that has proven to be an experimenters dream !!! Again, the circuit diagram is available via e-mail, just send me your request to [EMAIL PROTECTED], it’s a small dot jpg file, just 40 kilobytes,and I will soon follow it with a text file that will summarize all my experiments with this unique circuit, that has left all my visitors here at CO2KK’ s shack absolutely amazed… as a matter of fact , I had to print more copies of the circuit, as everyone coming here to my workshop seems to want a schematic diagram, after listening to the prototype !!!….Again, in case there was a little QSB , that is fading of the short wave signal, I have here the circuit diagram of the new cascode regenerative receiver built by Udo Peters in Germany, It is in dot jpg format and it’s a very small file, using only 40 kilobytes, so it can be sent as an e-mail attachment to Dxers Unlimited listeners around the world that want to see it. By the way, the only electronic component used in this interesting design that may be hard to find, is a 56 volts Zener diode regulator, that is feeding regulated voltage to the detector… Something that I have solved in two very practical ways, in one experiment, I used two 24 volts Zener diodes in series,or four 12 volts Zeners , and in another one, I used a Vr-75 glow discharge voltage regulator tube, in the case of the series connected Zeners, there was no need to modify the circuit, but in the case of the VR-75, I had to increase the value of the series resistor connected to the hot end Now, here is ASK ARNIE, Dxers Unlimited’s most popular section… Answering today a question sent in by another long time listener , from Canada… Amigo Gerry is asking a very interesting questions about UPS units, uninterruptible power supplies, that by the way, are ideal for handling amateur radio emergency communications by doing a very simple modification to the UPS units. Gerry wants to know if he can connect two UPS units to increase the available operating time when the electricity supply fails, and the quick answer amigo Gerry is NO, for many technical reasons… among them the fact that not too UPS units built by the same manufacturer are identical… My advice is to obtain a large sized battery, and connect it to the UPS unit by means of heavy cables and proper protection devices, and by that I mean fuses and a fast acting DC circuit breaker. For example, if you connect a heavy duty marine type deep cycle battery with a capacity of 180 ampere hours to a regular 450 volt ampere UPS unit, the system will be able to provide your emergency communications station with power for a very long period. You can optimize the emergency supply by connecting the radios that use 12 volts DC directly to the deep cycle battery, and other equipment that uses 115 volts AC to the output of the UPS. I hope amigo Gerry that you understand that heavy current DC circuits must be dealt with very carefully, as poor connections could lead to overheating and even may start a fire !!! So be extremely careful when working with direct current circuits that handle many amperes amigos. Then, here is the second “ trick” about UPS units… you can simply dig inside, find the wires that go to the internal rechargeable battery, and install two heavy duty binding posts , so that you can use the internal battery to provide power to your radios that use 12 volts DC. You don’t even have to turn on the UPS unit to operate your radios, and this is something that can be done very easily, but don’t forget to include a heavy duty fuse holder and a fuse of the right current rating between the battery and the external connections. Here at CO2KK my amateur radio station, I have modified two old UPS units, and they are now doing tripple duty, as battery chargers, external DC power supplies and of course, their intended primary service as uninterruptible power supplies for computers. Keep in mind that one of the reasons why amateur radio exists is that it provides emergency communications second to none, so everything you do to keep your amateur radio station ready to handle emergencies is a step in the direction of assuring the future of this aspect of our wonderful hobby : RADIO !!! …… Arnie’workshop today as crowded as ever, with no less than three radios waiting for repairs, and the micropower QRP rig connected to the dummy load with the key down to test its reliability… One of the radios to be repaired hopefully this coming week is a very interesting set, that forms part of a field intensity meter, covering from 30 to 300 megaHertz… Seems like a capacitor in the power supply failed, and the radio is providing audio output with a very high hum level… Repairing radios , new and old, and even antique ones, is one of the more than 81 ways that you and I enjoy this fascinating hobby amigos !!! Now , as always at the end of the show, here is Arnie Coro’s Dxers Unlimited’s HF plus low band VHF propagation update and forecast. Solar activity expected to continue to be at very low levels during the next several days. No significant sunspots regions on the far side of the Sun, and the same holds for the visible solar disk. The effective sunspot number has hovered at very low levels, and the recent fantastic sporadic E opening might be somehow related to this marked minimum in solar activity indeed. Solar flux is now around 80 units and moving steady up, expect solar flux to be around 80 units by mid week. The effective sunspot number near 25, , and we do see the effective height of the F2 layer reaching up to near 400 kilometers above the Earth’s surface at locations where the Sun is high above the horizon, something that makes daytime HF propagation conditions very poor indeed. !!! AND PLEASE… don’t forget to send your QSL card requests, radio hobby related questions and any ideas you may have to improve the Dxers Unlimited, so that it can be a better program to serve you and all the radio enthusiasts around the world !!! Send mail 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 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
