Radio Habana Cuba: Dxers Unlimited mid-week edition for October 24, 2000
By Arnie Coro, radio amateur CO2KK
Hi mis amigos, my friends, mes amis, this is the mid-week edition of your favorite radio hobby show. I am Arnie Coro in Havana and here is the menu for today: YES, we all enjoyed the superb, almost fantastic propagation conditions during the weekend... 10 meters open well into the middle of the night, 6 meter band DX worked by many stations, short wave listeners picking up harmonics of their favorite broadcasters in the 20 to 40 megaHertz range, you name it! Although the Sun's activity was not as high as expected for the peak of this rotation, the very quiet geomagnetic field -- and very possibly the effects of a meteor shower -- enhanced the HF plus 6 meters propagation conditions to the enjoyment of every radio hobbyist who had time to operate during the weekend.
Item two: What's a TRF radio, Arnie? A question sent in by a listener who tells me he is picking up Dxers Unlimited twice weekly on 9820 kHz just after the 0330 UTC re-run of the show... Amigo, I'll answer your question right here on this same frequency in a few seconds...
My sound engineer and producer is Margarita Delgado, I am Arnie Coro; stay tuned...
This is the mid-week edition of Dxers Unlimited, the radio hobby show that covers all aspects of this wonderful pasttime, from monitoring natural radio signals on the extra-low frequencies, to picking up the Spaceships to Earth communications links; from enjoying amateur radio on a shoestring budget to making friends halfway around the world operating PSK31 teletype with very low power... YES, there are more than 50 ways of enjoying this wonderful hobby, amigos!!! And here is one of them, learning about radio and electronics, so that you can homebrew some nice radio equipment. So, here is the question again: "Arnie, what's a TRF receiver?"
Well, my friend, a TRF receiver is a radio that amplifies the radio waves straight trough, without any frequency changes.... as simple as that, the Tuned Radio Frequency receiver simply boosts the signals picked up by the antenna and delivers those signals to a detector. The TRF or Tuned Radio Frequency receiver was one of the very first circuits used during the early years of radio, but today you won't find many TRF radios except perhaps in some very specific short range applications like garage door openers and electronic lock systems for cars. Believe it or not, the old TRF circuit is still in use, and it does work quite well under specific operating conditions. But you won't find a TRF receiver for sale by a major manufacturer of short wave radios, and there are many reasons why the TRF circuit is not used anymore for certain applications where selectivity -- the ability to separate between signals -- must be good... Radio experimenters still homebrew TRF receivers, and let me tell you that they can deliver excellent audio quality, but their main drawback is lack of selectivity. In the old days, TRF or tuned radio frequency receivers used several vacuum tube stages of amplification, each with its own tuned circuit, and those who used those radios had to peak each individual stage by carefully moving the variable capacitors back and forth until they obtained the maximum signal output.
You can homebrew a TRF radio receiver using either vacuum tubes, bipolar transistors or field effect transistors, and they will all work, especially if built for the AM broadcast band. My favorite TRF receiver uses two pentode vacuum tubes as RF amplifiers, a diode detector and a triode and a pentode forming a high gain audio amplifier. And let me tell you that it delivers an outstanding quality when tuned to the local AM medium wave broadcast band stations. A more modern version using two Field Effect Transistors, a diode and an integrated circuit audio amplifier works very well too, but it lacks the romance of the glowing-in-the-dark vacuum tubes... this newer version is definetely not a nostalgia radio!!!!
This is the mid-week edition of Dxers Unlimited, and here is item three: Our popular antenna section today will describe one the easiest to build wire gain antennas, one that provides excellent results despite its low cost and the fact that it requires just one tall mast, tree or building for its installation. This antenna is known as the asymmetric dipole; it is certainly a single band antenna by design, but with some extra care, you can make it work nicely on two bands. One of the most popular combinations for the asymmetric dipole is the one that is designed to operate on the 40 and 15 meter bands.
The asymmetric dipole, as its name clearly says, has one of its legs or arms longer than the other. In the case of the KK-4015, my own two-band antenna design, it has two wire elements on the short side that are one-quarter wavelength on 40 meters and one-quarter wavelength on 15 meters. These two wires are connected together and they are installed so that they are at the highest elevation above ground... Then the other arm or leg of the antenna is formed by a single wire that is three-quarters wavelength long on the 40 meter band. YES, this is a rather long antenna, and requires some real estate for installing it, but it is not installed horizontally; instead you install the antenna sloping down at a 45 degree angle in the direction you want to work the DX.... The KK-4015 antenna is fed via a coaxial balun choke coil with 50 ohm coaxial cable, and you must use pulleys so that the antenna's length can be trimmed for optimum operation.... You can make similar dual band asymmetric dipoles for 10 and 15 meters, and they will not require so much space, but the beauty of the KK-4015 is that it is an antenna that works well both during the daylight hours when 15 is open, and at night when the 40 meters or 7 megaHertz band is delivering the DX. Of course, during the peak months of the solar cycle 15 meters will remain open even well after midnight, but this is something that happens only during a short period. My KK-4015 antenna is beaming to Europe, and it has a rather broad horizontal pattern, so it covers from Eastern North America all the way to North Africa with good results... The KK-4015 dual band asymmetric sloping antenna is a low-cost solution for radio amateurs who cannot afford to install a Yagi or Quad antenna.
If you want to know more about the KK-4015 and similar dual band, low-cost wire antennas, just drop me an e-mail and I'll send you the Asymmetric Dipoles INFO PACKAGE ... If you don't have e-mail, then drop me a post card, and remember to include your return address and specify that you want the Asymmetric Dipoles INFO PACKAGE. Send your e-mail request to my easy-to-remember e-mail address, arnie@radiohc.org, and our postal address could not be easier -- just send a postcard with your signal report, comments about the show and the request for the Asymmetric Dipoles INFO PACKAGE to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
Now item four: A short dash to the workbench... still working on the big Marconi Signal Generator.... it spans from 10 megaHertz all the way up to almost 500 megaHertz, so after it is fully checked and calibrated it will be a very nice test instrument for the HF, VHF and lower UHF bands. Sitting right next to the Marconi is my single vacuum tube fun rig, a 6AG7 crystal controlled oscillator, delivering about 2 watts and with which I have made many contacts on the 40 meter band. Now, I am adding another crystal socket, so that it can use the very small HC 25 quartz crystals that I found for the 30 meter band, so soon you will hear CO2KK calling CQ DX on 30 meters CW with my QRP or low power single vacuum tube rig... The antenna for 30 meter work here is my FAN DIPOLE, a broadband antenna that covers from 10 to 30 megaHertz, and which is usually connected to my HF transceiver.
By the way, it was very nice to work many Dxers Unlimited's listeners who are amateur radio operators during Sunday and Monday UTC days... MY usual operating frequencies are 28.5 megaHertz on 10 meters and now I am using 21.4 on fifteen meters, again the new fifteen meters frequency is 21.400, 'way up the band where there is little activity and due to this fact, one can enjoy QRM free contacts... So look for CO2KK on both 10 meters and 15 meters whenever you have a chance to operate your amateur radio equipment, and believe me, the next 90 days are going to be the most exciting ones of the present solar cycle, so organize your schedule to be on the air as much as possible during November, December and January. You are going to be able both to work a lot of DX and meet many friends on the hambands, over which you can talk under excellent propagation conditions...
And now mis amigos, my friends, mes amis, as always at the end of the show, here is Arnie Coro's HF plus 6 meters propagation update and forecast: Attention please, your attention please, 6 meter band operators -- you must be on the alert for possible F2 layer propagation openings that will let you work some really nice DX... We will also see some nice Trans Equatorial Propagation enhanced by the solar activity; for short wave listeners, nighttime band conditions for easy listening will be better between 9.4 and 16 megaHertz, but just after local sunset and for about an hour, a propagation peak will bring nice DX signals on both the 16 and 13 meter bands... Solar activity will now probably start going down, and there are no signs of magnetically complex sunspot regions, so during the next 10 days we will see lower daytime maximum useable frequencies than the ones we enjoyed last week... Solar flux will start moving towards 150 units, but even as it moves down, there will be enough to keep the 10 meter amateur band alive for DX during many hours every day.
See you at the weekend edition of the show, don't forget to send your e-mail reports and comments to arnie@radiohc.org and a postcard to Arnie Coro, Radio Havana Cuba, Havana, Cuba. I'll be on 28.5 and 21.4 megaHertz ready to chat with all of you who already have a radio amateur station!!! And, if you don't have one yet, find out how you can obtain your ham radio license as soon as possible; amateur radio is one of the most fascinating aspects of the radio hobby, amigos!!!
Arnie Coro CO2KK
Havana, Cuba
October 24, 2000Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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