Radio Havana Cuba

Dxers Unlimited

Dxers Unlimited’s mid week edition for Dec 11-12 2007 By Arnie Coro Radio amateur CO2KK

Hi amigos radioaficionados around the world and in space… welcome to the mid week edition of RHC’s twice weekly radio hobby program, featuring today an update about the recent significant increase in solar activity, that sent the daily sunspot number up to 42 units, with the corresponding increase in the daytime maximum useable frequencies .

I am Arnie Coro, radio amateur CO2KK, and as always it is nice to have the opportunity of sharing with you about 17 minutes of on the air and on the world wide web time… Here is now item two: A totally portable loop antenna, that can be assembled and taken down in just a few minutes can be built using simple construction techniques that can be put in practice using simple tools. No need for a machine shop for building this one, that can be transported very easily, because its longest segment is just 40 centimeters long, so it fits easily into any travel bag… The use of high quality bolts and wingnuts, allows the fast assembly of the antenna, that can be made to reach a diameter as small as one meter or a large as two meters. The one meter diameter loop will work very nicely from 10 to 30 megaHertz, but its best performance will show above 15 megaHertz. Likewise, an intermediate size loop, just one and a half meters in diameter will provide good performance in the range

>from 10 to 15 megaHertz… The larger loop allows operating from about 6

to 12 megaHertz, and although it is more difficult to handle, it is certainly an ideal option for ham radio operators that enjoy backpacking and other forms of portable operation.

More about the SEGMENTED LOOPS with wingnuts later in this mid week edition of Dxers Unlimited… Stand by for a few seconds, I’ll be back after a short break For station ID…

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This is Radio Havana Cuba, the name of the show is Dxers Unlimited, and yes we do reply your QSL requests, via e-mail and also VIA AIR MAIL… We do have now a nice pocket calendar that you can also request via e-mail or by sending a postcard… Now here is item two in detail. The SEGMENTED LOOP WITH WINGNUTS, came out as an idea that challenged the usual way of building magnetic loop antennas. I discussed the effects of the many contacts that exist when using the segmented loop technology and several of my local radio engineering gurus said that for receive only antennas, the losses could be neglected but that the concept needed practical testing in the case of using this type of antenna for transmitting.

The first one that was built uses wide aluminum angle strips, each 50 centimeters long and with holes drilled at both ends.

The holes are for a 10 mm diameter bolt, and the succesive strips used to assemble the antenna are kept connected with the 10 milimeters diameter bolts, starwashers, pressure washers and a wingnut, so it is very easy to assemble and dismount the antenna…The areas that are joined have to be cleaned very well with fine sandpaper every time the antenna is assembled, and I must add that this loop antenna is not intended to be used as a permanent installation.

At the bottom of the loop the two opposing segments are joined via a small box where the tuning capacitor is placed.

For receive only applications, the capacitor can be an air spaced variable removed from an old vacuum tubes radio , but for transmission one must use a variable capacitor with wide spacing and ceramic or teflon insulation.

This type of antenna does require constant retuning, because it has a very narrow bandwidth at resonance, so the usual way of using it is by placing the antenna as near to the radios as practical. But beware that when used for transmitting, the antenna generates a very intense near field radiation, so it should not be used with powers above 25 Watts , in order to reduce exposure to electromagnetic radiation.

Homebrewing the SEGMENTED LOOP WITH WINGNUTS, can be accomplished with standard hand tools and an electric drill … My first prototype took about three hours to complete, and as a matter of fact the PVC mast that supports the antenna was more difficult to build than the antenna itself. For portable outdoors installations the antenna can be hanged

>from a tree using dacron or kevlar rope, but you can also take along a

portable mast that can be easily assembled at the site.

My tests using a 10 Watts power output transceiver on the 20 meters band with the wonderful PSK31 digital keyboard to keyboard mode with the SEGMENTED LOOP WITH WINGNUTS placed on my terrace, provided two way contacts with stations in 10 countries and three continents even though solar flux was at rock bottom levels. I then proceeded to install a compact loaded dipole that is half the size of a standard 20 meters band half wave dipole, and prepared a switching arrangement so that the two antennas could be switched back and forth immediately, so as to be able to compare signals, both when receiving and when transmitting. The results after many comparative tests showed that the time spent building the SEGMENTED LOOP WITH WINGNUTS, was worth every minute of it…My previous experience with the compact dipole for portable operation had left a very good impression, but the new loop antenna exceeded all my expectations, with the only inconvenience that if I wanted to move from the 14.070 kiloHertz PSK31 center frequency to the SSB voice segment of 20 meters, I had to retune the magnetic loop tuning capacitor for minimum standing wave ratio when transmitting or simple for maximum signal when receiving… Si amigos, yes my friends, oui mes amis… one inch by one inch that is 25 milimeters by 25 milimeters aluminum angle , 10 milimeters bolts and starwashers, pressure washers and wingnuts , about three hours of your weekend spare time , a high quality variable capacitor , a coupling loop made of number 8 copper wire and a length of 50 ohm coaxial connector for the particular radio you are going to use with the antenna are all the materials needed to homebrew it… The complete step by step building instructions with photos are now in the works, and soon to be completed into a dot pdf file that can be sent via e-mail, so if you are interested in the possibility of homebrewing this portable antenna, just send me an e-mail to arnie@rhc.cu, or a postcard VIA AIR MAIL to Arnie Coro , Radio Havana Cuba, Havana Cuba.

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You are listening to the mid week edition of Dxers Unlimited and here is item three of today’s show…Digital Television Dxing is a new addition to my list of the many ways one can enjoy our radio hobby… According to reports from several listeners, Digital TV is much more difficult to receive at long distances that analog signals, but I have not yet been able to test Digital TV DX myself, so can’t provide an opinion on this subject… anyway, the fact is that our hobby continues to develop and to bring up challenges, like this new one, Digital TV Dxing amigos… Item

four: Just a few days for 2007 to come to its end, and several of the

2008 handbooks editions are now circulating… The two most popular for short wave listeners are the World Radio and TV Handbook and Passport to Worldband Radio… I haven’t seen them yet, but I can tell you that buying one or the two of them is well worth the investment as the editors do make a big effort to provide the most up to date information for radio hobbysts.

For amateur radio operators, the Radio Society of Great Britain Radio Communications Handbook is in my humble opinion an essential consulting book at every radio amateur station… and certainly a more complete compilation than the ARRL Radio Handbook.

Item five: Here is LA NUMERO UNO, the most popular section of Dxers Unlimited… YOU have questions and Arnie tries to answer them as fast as possible. Today’s first question came from listener Jordan from Canada… He wants to know how the so called precipitation static can be overcomed… He explains that when it snows at his location, radio reception on the short wave bands becomes very difficult and that a local very experienced radio amateur told him that this was due to a phenomenon known as "precipitation static"… Well amigo Jordan your ham radio friend was absolutely right… and it can also happen when it is raining at a time that the atmosphere is paradoxically with a very low water content… snow static, and rain static can’t be cleared by any known method that I know about… You simply must relax and wait until the noise clears amigo !

The second question came from the United Kingdom, where listener Milton, who picks up our 11760 kiloHertz frequency during the early morning local time, wants to know about the relative popularity achieved by the many different digital communications modes that amateur radio operators have now access to and are allowed by their telecommunications administrations to use. Well amigo Milton, without any doubts the PSK31 keyboard to keyboard mode is the most popular one of them all, with more and more ham radio operators around the world using it… The PSK 31 mode can be implemented even using old computers and simple to install and operate software, and after a few QSO’s you can become familiar with it and its outstanding capability to provide DX communications using very low power. Other more sophisticated digital modes require more bandwidth and have so far not become so popular . Digital voice is now making slow headway , and a recent version of a digital voice mode that uses a less than one and half kiloHertz bandwith is now undergoing regular testing by radio amateurs. So far the experiments show that the software used to encode and decode the voice is good enough to produce practical results, but it also seems that it does require more polishing on the part of the software developers as decoding isn’t easy at all and the voices that come out of the loudspeakers are very, very similar to robots of science fiction films !

And now amigos, as always at the end of the program , here is our exclusive and not copyrighted , in the public domain, Arnie Coro’s Dxers Unlimited’s HF plus low band VHF propagation update and forecast… Solar activity is hovering between low and very low… There is a very interesting sunspot emerging from the limb of the solar disk that will be capturing the attention of solar scientists during the next several days because of its high solar latitude location. Solar flux was around