Radio Habana Cuba: Dxers Unlimited Midweek edition for July, 18 2000
By Arnie Coro, radio amateur CO2KK
Hi amigos, welcome to your favorite listener oriented radio hobby show on short wave. I am Arnie Coro, radio amateur CO2KK, your friend here in Havana and host of this twice-weekly program, featuring the most up-to-date HF plus 6 meters propagation forecasts....
Here is item one: Damage assessment following the huge solar flare that disrupted radio communications during the weekend reveals that hardware impact was not as bad as scientists expected. Nevertheless, solar researchers keep warning that during the peak year of cycle 23 we may expect more X type solar flares, and some of them might be reaching up to the X9 category. And now that I am talking of solar flares, the forecast calls for more of them coming, mainly from solar active regions 9077 -- which is declining in activity -- and 9087 -- which is now growing in size. For all of you who enjoyed the exceptional aurora borealis propagation that developed at high and mid latitudes during the severe geomagnetic storm, congratulations for the many new loggings!!! It was nice to receive such nice reports, and comments about how useful Dxers Unlimited's special weekend edition was for those of you who were not aware of the solar flare associated storming.
Item two: Once again, don't pass up the opportunity: Any old equipment that is offered either free of charge or at a very attractive low price, should be added to your stockpile of radio gear... If it can be repaired, good for you -- in some cases you can explore its value as an antique, and if it does not qualify, then it may provide you with lots of electronic components for your experiments.
Item three: Double diamond antenna for TV reception: It is a very easy to make an antenna that can be assembled in a few hours, providing excellent broadband reception. More about a specific design of the double diamond for the high band VHF TV channels later in today's edition of Dxers Unlimited. My sound engineer and producer is Jose Izquierdo; I am Arnie Coro reaching you today via remote pick up.
You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited, and here is item three in detail. The double diamond QUAD antenna configuration makes a very nice wideband system for receiving local VHF hi band TV channels, the antenna is made from standard household PVC insulated wire, and each of the two diamond-shaped elements has 40 centimeters, or about 15.75 inches, per side. Both elements are identical, and the feedline is connected at the center of the two elements. You can use 75 ohm TV-type coaxial cable and the standing wave ratio will stay at very reasonable values, which will not affect reception. I used PVC pipe for supporting the prototype TV double diamond, drilling small holes at the ends of the crossarms to pass the wire through them.
The antenna is very rugged, and has endured heavy tropical weather without any failures. The only precaution that you must take is to properly solder and then protect from the weather the connection of the two elements and the coaxial cable downlead. Purists will tell you, and they are right, that the double diamond is a balanced antenna, and that the coaxial feeder cable is an unbalanced line, and that's true, but you can get away with direct coaxial feed, just by providing about 6 or 7 turns of the cable wound on top of a small length of PVC pipe of a diameter between 50 and 75 milimeters -- that is, from 2 to 3 inches.
A single double diamond TV antenna of this type will provide good reception of local TV signals and has an added advantage over the TV rabbits ears, because it can be oriented to cancel reflected signals that generate ghosts on the TV picture. It is amazing to see how two lengths of wire and a few bits and pieces of PVC pipe can provide such excellent TV reception! If you need more information on the VHF HI Band Double Diamond Antenna just e-mail to: arnie@radiohc.org or send your request via Air Mail to Arnie Coro, Dxers Unlimited, Radio Havana Cuba, Havana, Cuba.
And now here is item four, the very popular "you have questions and Arnie has answers" section of this show. The question came today from a listener in Northern Mexico who tunes to our 9820 kiloHertz Pacific coast of North America broadcast, which runs from 05 to 07 hours UTC. He asks:
Arnie Coro, when I am listening to RHC English Language Broadcast on 9820 kiloHertz from 01 to 05 UTC, my receiver S meter moves normally between S6 and S8; then, at precisely 05 UTC, the signal here in Northern Mexico jumps to between S9 and S9 +20 decibels... Can you explain why this happens? Do you do anything to your transmitters and antennas at that precise time every day???Well, amigo Raul in Baja California, Mexico, that's exactly what happens! At that time, 0500 UTC, we disconnect very briefly the 100 kiloWatt transmitter and switch to a different antenna. From 00 to 05 UTC, we use that transmitter with an antenna beaming to 348 degrees, sending our signal to Central North America. Between 00 and 01 the program is in Spanish, and then at 01 we switch to English until 05, all with the same antenna. Then at 05, as I explained earlier, the antenna is changed to provide coverage to the Pacific Coast of North America, beaming to 315 degrees. Due to the highly directive type of curtain antenna, your receiver shows a marked increase in signal strength when the antenna in use is the one beaming our signal to your area. I hope this answers your question, amigo Raul!
Now here is item five of this mid-week edition of Dxers Unlimited, reaching you via a remote pick up link: Another possible delay in the already very-much-delayed amateur radio super satellite. Seems like Ariadne Space found some problems in one of their launchers, and decided not to risk any future satellites, thus delaying flights until fault-finding is completed. In the meantime you can enjoy the fun ham satellites that provide very short-duration contacts when they fly overhead at high speeds and low altitudes above the Earth.
Item six: Our technical topics section today is answering a listener's request for information about something he heard from an old-timer... He asks:
Arnie, an old-timer at the radio club was telling the young crowd that at one time, during vacuum tube development, some tube types were designed to operate using very low plate voltages, reaching as low as 10 to 15 volts, and yet they worked nicely.Well, mi amigo from Virginia, YES ... your old-timer friend was right. During the late nineteen-fifties, several low plate voltage tubes reached the automobile radio market, and they were designed so that car radios would not need a high voltage power supply for the tubes. Those radios used the first output power transistors for their audio output stages, and the low plate voltage vacuum tubes for the rest of the circuit. Not too long ago, I found a box full of those low plate voltage tubes and I must tell you that after more than 40 years in storage, they all have tested in excellent shape... so maybe in the not-too-distant future you will be listening to yet another very low power or QRP transmitter from CO2KK, using those very low plate voltage tubes... And before I forget, the tubes do require powering up the filaments, so they do drain a lot of current from the 12 volts DC power supply. I hope this answers your question, and if you ever come across one of those old automobile radios that use tubes and no high voltage power supply, you can be sure that the tubes are the low plate voltage types that saw a very short period of use, just before high quality, high gain, stable and reliable transistors for radio frequency work came into existence.
And now amigos, just before going QRT, here is Arnie Coro's exclusive and not copyrighted HF plus 6 meters propagation update and forecast. Solar activity will continue moving between Moderate and possibly HIGH levels. The solar flux has moved upwards, when it was supposed to be moving down, once again showing how difficult it is to make accurate forecasts of solar activity. Solar active region 9087 is growing in size and may generate flares of high magnitude during the next two to three days. The solar flux is hovering near 230 units and moving slowly up, making this rotation of the Sun the most interesting one of the whole cycle so far. I am sure that many of you remember when I warned here about how important the upcoming solar rotations were, and now you see how this one generated the X6, almost X7, type solar flare that was the most important event so far in the whole cycle, and the single most important flare since 1989. Be ready for more action, and now, listen to the forecast for the next two to three days:
Expect improved short wave propagation, with maximum useable frequencies moving up, and once the geomagnetic storm was over, we are seeing much lower ionospheric absorption and the typical good propagation seen after storming. Be on the lookout for some really nice DX conditions to occur very late in the evening your local time.
prepared 18 July; received 21 July 2000
Arnie Coro CO2KK
Havana, Cuba
18 July, 2000Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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