Radio Habana Cuba: Dxers Unlimited Weekend edition for May 13-14, 2000
By Arnie Coro, radio amateur CO2KK
Hi amigos! Hola!!! Welcome to the weekend edition of your favorite, listener oriented radio hobby show on short wave. I am Arnie Coro here in Havana, ready to provide you with about seventeen minutes of all radio hobby related information. Here is item one: Solar activity still in the LOW to MODERATE range, but things are picking up, after the Sun spent quite a few days in an almost spotless condition, something that really puzzled scientists, as they certainly did not expect this to happen so near to their predicted solar cycle maximum. Solar flux is now near the 200 mark, but it is going to take in my opinion at least two more days for us to enjoy better short wave propagation on the higher bands... more HF propagation information as usual at the end of the show...
Item two: Six meters opening up again via sporadic E, according to reports received from Europe, North America and the Caribbean, plus my own daily observations, the sporadic E clouds are once again providing that very interesting propagation mode for TV and FM band Dxers, and of course, to amateur radio operators too...
Item three: CO3JK, Javier, an enthusiatic 30 meter amateur band operator is now installing a 30 meter band elongated loop that I designed for him, stay tuned to learn more about that interesting antenna system that is easy to build, and offers excellent performance for DX work... Now, a short musical interval is coming up, Margarita Delgado is my sound engineer and producer, this is Radio Havana Cuba... stay tuned...
Yes amigos, this is the weekend edition of Dxers Unlimited, reaching you at the time that short wave propagation conditions are not very good due to low intensity geomagnetic storm in progress, and here is item three, the CO3JK 30 meter band elongated loop antenna. It is simple to build, matches 50 ohm coaxial cable without any problems, or if you prefer it can be fed with open wire transmission line and then be useful on several bands for transmitting and short wave listening too. Do not forget that many amateur radio operators like Javier CO3JK and myself also enjoy listening to international short wave broadcast stations too, and that we use our amateur radio rigs to enjoy that aspect of the hobby too.
Well, here is some information about this rather compact antenna, that radiates with a low departure angle, despite the fact that it does not need very high masts, as a matter of fact, CO3JK uses home brew masts made from bambusa-bambusa, well bamboo, bambusa-bambusa linnei is the scientific name that botanic experts give to bamboo. Javier's masts are made of several sections of heavy cuban bamboo or cana brave, reinforced between sections by short lengths of aluminium tubing of appropiate diameter. The masts are some 9 meters high, or for those of you that still think in English measuring units almost 30 feet high. Javier has two of those masts, separated by just twelve meters or almost 40 feet.
The rectangular loop's vertical sections are 5 meter high, and the horizontal sections are 10 meter long. So, CO3JK's loop is shaped like a rectangle that has its short sides of 5 meters length, and the long sides of 10 meters length. The short sides are the vertical ones, so that allows the lower horizontal section to be placed at 4 meters above ground, which while not ideal, is nevertheless good enough to make the loop generate an adequate vertical take off angle.
Now, listen how the antenna is fed... CO3JK's 30 meter band loop is fed using 50ohm coaxial cable, but you can use low cost TV type 75 ohm coax if you wish too. The feedpoint is at one of the upper corners of the antenna, as we want to take advantage of the elevated feedpoint placing the high current as high as possible!!!
As I said a while ago, the 5 meter high and 10 meter long rectangular loop can be also fed with open wire line, something that will allow its use on other frequencies too. Using the coaxial cable feedline, the antenna is a single band antenna, capable of low SWR or standing wave ratio operation only on the 30 meter ham band that spans from 10.1 to 10.150 megaHertz. Similar aspect ratio loops can be designed and built for other amateur bands, and they offer to their users several important advantages over the classical single band half wave dipole.
The first and most important one is that the rectangular loop is a very quiet antenna for receiving purposes, due to the fact that it is a closed element, then add to this that it does not need very high masts, plus the fact that even when placed at a relatively close distance from ground, it does generate a nice and clean, low take off angle which is much better for DX work than the vertical pattern of a half wave dipole at the same height. Now, add to all this advantages its low cost and very easy installation, direct coaxial cable feed using either 50 or 75 ohm cable, and you will realize that the rectangular one wavelength loop is a very nice all around antenna. CO3JK, Javier has just a 15 watt CW and SSB rig, so if you ever come across his signals on 30 meters, you will know how well the rectangular loop is working using almost QRP power!!!
Do you want to know more about ELONGATED LOOPS? well, then just e-mail me to arnie@radiohc.org and I'll be happy to send you a text file with the HOW TO information about how to design, build and install one wavelength long rectangular elongated loop antennas for the frequency range between 3.5 and 50 megaHertz. again the Internet e-mail address is arnie@radiohc.org,and if you are not yet in cyberspace, send your request for the ELONGATED LOOP text file via AIRMAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
You are listening to Radio Havana Cuba, coming to you via our short wave transmitters in Cuba. this is Dxers Unlimited's weekend edition, and this is item four: The ever popular, actually the second most popular section of the show according to a recent poll, la numero dos, number two most popular section of this show... YOU HAVE QUESTIONS, and Arnie has answers.
Here is today's question:
Arnie, is it true that there is a diode mixer circuit that uses the local oscillator at half the operating frequency that one wants to receive?
ANSWER: Yes, it is the Polyakov mixer, using two antipararell connected diodes, and let me tell you that it works great even at microwave frequencies if you select the appropiate diodes. The so-called POLYAKOV or harmonic mixer lets you design and build a very nice direct conversion receiver for the amateur bands, which uses the local oscillator at half the operating frequency... for example, a compact 29 megaHertz receiver for picking up amateur radio satellites operating on that segment of 10 meters, uses the VFO or variable frequency oscillator on 14.5 megaHertz, which is a lot easier to stabilize than a VFO operating on 29 megaHertz. I am working on a prototype POLYAKOV antipararell diode mixer amateur band receiver, that when finished will be uploaded to the web.
And now amigos, as always, at the end of the show, here is Dxers Unlimited's most popular section of the show among its worldwide audience, Arnie Coro's HF Propagation update and forecast. As you have surely found out all by yourself by monitoring the HF bands Solar flux and sunspot numbers were sharply lower over the past ten days, but are now already higher.
Solar flux reached a record breaking for year 200 LOW on Saturday, May 6, when the three readings for the day were 126.3, 126.8 and 126.7.But it was the noon 126.8 reading the one that was taken, as always as the official flux for the day.
Daily solar flux values have not been this low since the second day of October 1999, when it the flux reached just 126.3.
Another interesting number that provides a lot of information is the total sunspot area visible on the solar disk.
These numbers are expressed as millionths of the solar hemisphere. A LOW of 130 millionths visible sunspot area was recorded on May 7. And let me tell you that Sunspot area has not been this low since September 30 and October 1, 1999. This value, just 130 millionths of the Sun's visible hemisphere covered by sunspots represents in practical terms a nearly spotless sun, and is equivalent to.013 percent ofthe visible surface. Just for comparison purposes a short time back, April 23, sunspot area number was 2860, representing 22 times the visible area of the May 7 value.
NOW, does this means that the solar maximum has already passed along? Well, NO... even during the solar maximum months, activity can jump around quite a bit. I just wanted to quote these figures as during the past ten days my arnie@radiohc.org e-mailbox was flooded with e-mail messages asking what was really happening with short wave propagation.
NOW, here is the forecast for the next 5 days... solar activity will continue to move UP, oscillating from LOW to MODERATE, solar flux should reach the above 200 mark, and stay there. We will witness the effects of yet another geomagnetic disturbance Saturday and Sunday, and perhaps part of Monday, with HF propagation going back to normal by Tuesday.
Be on the lookout for possible rare DX stations during the geomagnetic storm that may be in progress at the time you are listening to this show, and later on... For 6 meter band operators a special ORANGE alert, as the probability of 50 megaHertz DX during the next 96 hours will increase significantly.
See you on 6 meters if the band opens, and on the 20 meter band during the time frame between 0300 and 0400 UTC around 14180 to 14190 kiloHertz... hope to work many of you on the ham bands, amigos!!!
Arnie Coro CO2KK
Havana, Cuba
May 13, 2000Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba
PO Box 6240, Havana, CUBA 10600
phone: 53-7-814243
phone res: 53-7-301794
e-mail: arnie@radiohc.org
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