RADIO HABANA CUBA
DXERS UNLIMITED
WEEKEND EDITION
SATURDAY, APRIL 13, 2002
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hi, amigos radioaficionados worldwide! Nice to have you here with me listening to the weekend edition of Dxers Unlimited, your favorite radio hobby program! I am Arnie Coro radio amateur CO2KK, your friend in Havana, get ready now for about seventeen minutes of all radio hobby related information...
Here is item one: Big sunspot detected on the far side of the Sun! Helioseismic instruments make this unique scientific achievement possible... of course the ideal way to have a complete view of the solar sphere will be to launch a space vehicle that could relay back to Earth a digitezed image of the side of the Sun that is not seen from Earth... and that amigos, may come some time in the future to further complete the outstanding instrumentation that has made possible studying solar cycle 23 much better than any of the previous 22 cycles.... And scientists are now preparing much better solar terrestrial interactions forecasts than ever before, thanks to the availability of instruments that make this possible.
Item two: You have heard this here many times... radio need not be an expensive hobby at all... today, I'll describe another simple short wave receiver that may be built at low cost too...
Item three: The antenna topics section of Dxers Unlimited is a very popular one indeed, and this Dxers Unlimited's edition will bring you more information about the V antenna, described by engineers as the simplest possible beam antenna...
This will be followed by item four: Our "YOU have questions" and Arnie tries to answer them as soon as possible, with the answer to a question sent in by a long list of listeners... The question has to do with a new threat to radio reception, the use of power lines to transmit computer data...
And as always at the end of the show, listen to Arnie Coro's Dxers Unlimited's HF plus 6 meters propagation update and forecast... Margarita Delgado is my sound engineer and producer, standby for a few seconds. I'll be back after this short musical interval.
This is the weekend edition of Dxers Unlimited, and here is item two... Yet another simple yet effective short wave receiver... This one uses an easy-to-assemble front end filter that makes a lot of difference as compared with the more common low cost simple radios... The TRIPLE TUNED SPECIAL, the TTS receiver, has a lot of front end selectivity and a nice but easy to build resistive signal attenuator... The three tuned circuits that form the input filter are very lightly coupled, and although this increases the signal attenuation, the fact is that it does help to make a much better receiver...
In version ONE of the TTS, the TRIPLE TUNED SPECIAL, I used three variable capacitors, one for each of the tuned circuits, high Q coils properly shielded from each other as to minimize stray coupling and very small air dielectric capacitors to couple the three tuned circuits together... The input filter is connected to a step attenuator via a variable link, and similarly the output at the third tuned circuit is connected to the radio frequency amplifier stage via a low impedance link...
Tests show that replacing the elaborate triple tuned input filter and attenuator with the more common single tuned circuit used by low cost receivers degraded the performance of the receiver significantly. Also, a ham radio friend asked me to install the filter ahead of another receiver, an old radio with a single input tuned circuit, and sure, the radio's performance was a lot better. Building the TTS receiver involves a lot of metalwork, as no compromise was made regarding the use of small sized components...
The heart of the radio, from which it got its name, is precisely the triple tuned filter and attenuator tightly shielded box, with its three large high Q coils wound on ceramic coil forms and its three individually tuned air spaced variable capacitors... An old-timer who saw the huge filter-attenuator said that it looked much like the tuned radio frequency receivers of the early days of radio, except that no amplification is included between the tuned circuits.
The prototype TTS tunes from 6 to 12 megaHertz and has no bandswitching... So the experimental receiver can pick up short wave broadcasts on the 49,41,31 and 25 meter bands, plus the 80, 40 and 30 meter amateur bands... No attempt was made to introduce another set of coils or bandswitching because that will severely degrade the performance of the optimized triple tuned input filter...
The rest of the receiver is quite straightforward, using a grounded gate field effect transistor as the radio frequency amplifier stage, a double balanced mixer, and two stages of intermediate frequency amplification using a low cost ceramic single side band filter... The injection for the mixer comes from a three stage Field Effect transistor oscillator running on the high side of the input frequency.
As this is an experimental receiver, the detectors used included just a simple two-diode AM detector and a double balanced four-diode product detector for CW, SSB and Digital Modes, the audio is quite straightforward, and at present it does not contemplate the inclusion of audio bandpass filters... The idea was to have a sort of test bed for the triple tuned input filter and attenuator, because this part of the TTS receiver could be all by itself, a worthwhile addition to existing low cost commercial receivers...
After a couple of weeks of trying the triple-tuned input filter and attenuator connected via coaxial cable to a small rather low cost portable short wave receiver, I am now quite sure that it is a really worthwhile project... Si amigos, yes my friends! Adding this nice not-too-small box ahead of a low-cost portable radio will dramatically improve its performance, as it will reduce front end overload to a bare minimum and bring crossmodulation problems to an end!!!
Send your radio hobby related questions, signal reports, QSL requests and comments about our programs to: arnie@radiohc.org or via AIR MAIL to Arnie Coro Radio Havana Cuba, Havana, Cuba.
Now here is the antenna topics section of Dxers Unlimited... What's the simplest possible beam antenna? The two-element YAGI, the two-element phased array, or the simple V antenna... Antenna experts affirm, and I agree with them, that the two-wire V is the simplest of them all, and they do insist that a terminated V antenna sloping at an angle between 15 and 30 degrees with the adequate apex angle is capable of an amazing performance, considering its simplicity....
Many years ago when I began experimenting with long range television reception, quite by accident I found that the V was a nice antenna, when half of my poorly built rhombic fell to the ground, and only half of it, that is, a V was working. Even very limited length per leg V antennas are good performers, and the sloping version is easy to install, as it requires just a single tall mast, tower or tree as the main support...
Playing with antenna simulation software, I came across a simple sloping V antenna for the range from 25 to 75 megaHertz, using just two wires that are 12 meters or just a little less than 40 feet long... Both wires are terminated with 300 ohm non-inductive resistors and the antenna is fed using 400 ohm ladder line... The computer-generated graphic of this V antenna horizontal pattern looks so good, that soon I may have one installed here at CO2KK to be connected permanently to my 10 and 6 meter band propagation detector receivers!
I hope this answers the question about the simplest-possible wire beam antennas... As you have just heard, the V does not require a boom like the typical Yagi or collinear, and it has another great advantage over the other simple wire beams: the terminated sloping V is certainly a broadband antenna by all standards!!! Disadvantages: Size, and that the V beam is definetely a non-rotatable antenna at all!!!
You are listening to the weekend edition of Dxers Unlimited amigos! And here is our very popular "YOU have questions and Arnie tries to answer them." Today's question has to do with what is already a big threat to radio reception coming via so-called power line digital signals transmission systems... This lethal combination of the classic carrier current radio frequency systems. used since the early days of radio by power companies and campus radio stations, when used with digital signals may cause a lot of trouble to radio reception in urban areas... As a matter of fact, several similar systems intended for domestic use are already available, and all tests show that they are definetely a menace to radio reception! The reason why this system is promoted is none other than a matter of saving the cost of installing wired networks, or using the much more expensive microwave local area networks...
Even when properly designed and installed, there is no way for the power line data distribution systems to avoid a head-on confrontation with users of the radio spectrum!!!! As a matter of fact, all tests performed so far with professional spectrum analyzers show that the contribution to radio frequency pollution by such systems far exceeds the maximum allowed by good engineering practice... So here is your friend's Arnie Coro's advice: Don't buy yourself a home local area network, or LAN system, that uses power line distribution, and by all means try to persuade everyone you know to avoid them, too!!!
And now amigos, as always at the end of the program, here is Arnie Coro's Dxers Unlimited's HF plus 6 meters propagation update and forecast: Let's start with the magic band... Trans Equatorial Propagation from the Caribbean to South America and from the Mediterranean to South Africa is happening now every day and will continue for about two more weeks... The sporadic E season is just around the corner, too... The number of sunspots seen on the solar disk continues to be rather high, and at least one big sunspot is now clearly detected on the far side of the Sun.
HF propagation conditions continue to be rather good, with the occasional fadeout and disturbances caused by solar flares and associated coronal mass ejections that send streams of charged high speed particles towards Earth. The region of the short spectrum from 15 to 22 megaHertz continues to be wide open during your local evening hours to many parts of the world, and the daytime MUF is still hitting the above 30 megaHertz mark!!! So, enjoy this little extra that the Sun is giving to us as a consequence of solar cycle's 23 second peak!!! And maybe, yes, maybe the Sun will perhaps surprise us with yet a third PEAK too...
See you on 15 meters around 21.295 plus minus 5 kiloHertz, on 10 meters 28.500 plus minus 5 kiloHertz and also perhaps on 20 meters around 14205 plus minus 5 kiloHertz... If you have not yet obtained your amateur radio license, start studying for the test today!!!
Prepared 13-Apr-2002; received by NY Transfer News 16-Apr-2002, 15:07 EDT
Arnie Coro CO2KK
Havana, Cuba
April 13, 2002Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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