Dxers Unlimited
Dxers Unlimited's weekend edition for 11-12 September 2007
By Arnie Coro
radio amateur CO2KK
Hi amigos short wave listeners and radioaficionados around the world.. nice to have you listening to our midweek edition of Dxers Unlimited, coming to you from Havana. I am Arnie Coro, radio amateur CO2KK your friend here in Cuba, now ready to provide you with about 17 minutes of on the air and on the web time devoted to our wonderful and fascinating hobby : RADIO !!! Here is item one: Equinoctial propagation conditions now in full swing and already many radio amateur are enjoying daytime
DX on the 20, 17 and 15 meters bands.. even when solar flux is hovering at very low levels just at minimum, minumum solar flux and zero sunspots .. At the same time , and due to the very low solar activity , the 160 and 80 meter radio amateur bands are providing excellent DX during local nights amigos despite the still high summertime static levels !!!
So, seems like at this particular moment we are able to enjoy the best of both worlds, daytime DX on the HF range, and nightime DX on 160 and 80 meters. My good friend AKI, CO2 Charlie India, told me Saturday morning during a QSO we had on the local two meter band repeater that he had worked several Japanese stations on 80 meters CW at sunrise local time here in Havana... And this contacts are possible due to rather low ionospheric absorption and the enhancement provided by the so called
gray line or terminator line propagation, that is the line that separates DAY from NIGHT on planet Earth,actually it is not exactly a thin line at all, it's like a band extending both sides of the actual terminator what makes propagation possible with very low attenuation between locations that are at sunrise and sunset at the two ends !!!
Item three: I recently went to Matanzas province.. Matanzas is located to the East of Havana and is the province where the world famous Varadero Beach at the Hicacos Peninsula receives hundreds of thousands of tourists from all over the world.
The Varadero Amateur Radio Club is often visited by tourists that are also ham radio operators and want to know their Cuban colleagues... Matanzas has several 2 meter band repeaters installed , but two of them are particularly useful when one is traveling by car , as they can be easily reached using a low power hand held FM transceiver. Those amateur 2 meter band FM repeaters are also particularly helpful during the hurricane season, as they provide very effective communications between
hand held, mobiles and fixed stations.
I had the opportunity of talking to many Matanzas radio amateurs during my one day trip to their beautiful province, and as always enjoyed one of the more than 81 ways you and I can have a good time on the radio... mobile ham communications !!!
Item four today will be our antenna topics section, and later item five will answer listeners questions...at the end of the show, as always, our exclusive and not copyrighted HF plus low band VHF propagation update and forecast will bring the program to its end... Stay tuned, I am Arnie Coro in Havana, more of Dxers Unlimited's midweek edition follows in a few seconds..
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Si amigos, this is the midweek edition of Dxers Unlimited coming to you from Havana... Now here is our antenna topics section... today I'll tell you about how you can make yourself a compact antenna that will allow you to operate an amateur radio station or to monitor Dx on the lower frequency ham bands, the ones that are now much more significant as solar cycle 23 comes to an end right at this very moment... My new version of the KK-COMP antenna uses a very well engineered combination of inductive and capacite loading, so its efficiency is certainly above
the average compact antenna for the lower frequencies.
Another neat trick that I used when designing these antennas is to make the diameter of the loading coils as large as practical, so that they will also contribute to radiation and not only do their job as inductive loading to help shorten the antenna.
The experimental version of the KK-COMP antenna benefitted from a very nice experiment, because I made it for the 10 meter band... Doing that in order to be able to test the scale model of the antenna easily. The use of actual, physical scale sized antenna models is in my opinion a reliable method, that makes a nice complement to the use of antenna modelling software.
A full size 10 meter band dipole antenna requires about 5 meters of wire, 2.5 meters for each leg of the dipole... That's for those of you still thinking using feet and inches, is about 16 feet overall length , or 8 feet each side of the center insulator. I decided to reduce the size of the 10 meter band antenna by 50 percent, in other words to make it just 2.5 meters or about 8 feet long, while at the same time retaining a high radiation efficiency. How could I tell if the compact version of the antenna was really efficient or not ?
Well, very easily , by using a test instrument known as a field intensity meter , and a full size antenna used as a reference. The procedure used is very simple, you set up the full size antenna up and in the clear, feed it with 10 Watts of 28.5 megaHertz radio frequency energy and measure the field intensity at a certain distance, typically no less than 10 wavelengths away from the antenna.. and that's
about a city block away in this case.
Then you replace the reference full size dipole, install it at exactly the same height , and proceed to test your experimental compact antenna, measuring the field intensity and writing down the resultant figure.
The a little mathematics will tell you if your compact antenna is doing its job... You can be sure that the compact antenna will never be as efficient as the full size one, but the fact is that my design provides an efficiency that is really utstanding when one considers that the compact KK DASH COMP antenna is half the size of the 10 meter dipole...
After the measurements were finished I proceeded to operate my 10 meter rig using the KK DASH COMP, and reports coming from radio amateurs in eleven different ountries, from Canada to Argentina, and from Spain to South Africa confirmed that the very small antenna is working very well..
The KK DASH COMP uses a combination of two loading coils and two spiral wound capacity hats .The loading coils are located at the center of each wire element, and the spiral wound capacity hat are placed at the ends.
The use of a combination of inductive and capacitive loading is what makes the antenna very efficient, because the presence of the circular spiral wound capacity hats at the ends of the elements makes possible to reduce the number of turns of each loading coil, and that in turn reduces the losses introduced by the coils.
I must add that the small sized KK-DASH COMP antenna with its two end loading spirals is a very nice looking signal grabber, as the 30 centimeter diameter spirals give it a very distinctive look indeed... UPSCALING the design results to the 40 meter band gave me a 7 megaHertz antenna that is the size of a standard 20 meter band dipole, and that according to my measurements is just -2 dB down from the full size radiator... And that minus 2 dB difference is easily compensated by increasing the transmitter power output just a bit. For the many radio amateurs around the world that suffer from lack of real estate to be able to install full size lower bands antennas, the KK DASH COMP is a practical, low cost, solution that you can homebrew during a single weekend... If you found this information useful and want to know more about my KK DASH COMP compact inductive and capacitive loaded antenna, just send me an e-mail to arnie@rhc.cu, or an AIR MAIL postcard to Arnie Coro, Radio Havana Cuba,Havana, Cuba.
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Reaching you via short waver, and also available on the world wide web and via the Hispasat I D satellite,transponder 79 vertical polarization, in English from 05 to 07 UTC, this is Radio Havana Cuba, the name of the show is Dxers Unlimited, and this is our modest twice weekly contribution to the development of the radio hobby amigos !!!
Here is now ASK ARNIE, THE most popular section of the program ,. according to what your letters and e-mail messages tell me evey week.. Question one today: Came from several listeners located in Australia, New Zealand, Japan, the USA and Nigeria... they all want to me to provide an answer to their question.
They want to know if it will be worthwhile to buy a radio receiver that is not operating , in other words a broken down radio... Each of those that wrote quotes a particular model of radio, and as expected, the price asked for the radios was quite reasonable.. and two of them just had to pick up the broken radios given away by friends. Well amigos, first things first...
When buying or picking up for free a radio receiver that is not operating to its full factory parameters you are certainly running a risk...but if the price is low enough, or the radio is just given away to you I can assure you that it will be a win-win deal,because , and now listen carefully to this, in the extreme case that the receiver may not be repaired, you will end up with lots of useful electronic
components that can be effectively recycled and used for many radio hobby related experiments.
The other side of the coin will show you that many radio receivers, especially those built before 1970, can be rather easily repaired and restored back to like new or even better than when new conditions..For example, so called boat anchors, or old vacuum tube communications type receivers,often come back to life by just changing a few electrolytic capacitors,( something that is absolutely essential to do) then replacing paper bypass capacitors and checking the vacuum tubes for emission and transconductance. First generation solid state communications receivers are also a lot easier to repair than the most modern microprocessor controlled radios. My advise is that you stay away from the more modern receivers , because they are very difficult to repair, and in many cases they can not be put back to work because of the way they were built !!!
Follow your friend's Arnie Coro advice and look around at hamfests and flea markets, garage sales or even ask friends if they happen to have an old radio somewhere in the attic or garage... You will be pleasently surprised when that old radio comes back to life giving you many hours of listening enjoyment... AND, if you don't have too much space to keep them, then the repaired radio can be passed along to a newcomer to the hobby at cost, or perhaps for free !!!
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QSL,QSL on the air to the many Radio Havana Cuba listeners that have sent so many nice signal reports recently... Our Chief Engineer at the Bauta transmitting station is very happy with the reports I have forwarded to him and his crew...
And now as always at the end of the show, our exclusive and not copyrighted HF propagation update and forecast.. the daily optical sunspot count is now ZERO , and the effective sunspot number or SSN is now only 4 . The planetary A index on Friday was 2 , and it seems like it will be staying at very low levels.
Microwave solar flux will be moving slowly up to values around 65 to 70 units, Again amigos we are now reaching the autoum equinox, here in the northern hemisphere. So,its time to be active on the radio amigos, you can always return to the workshop and play with your equipment when HF propagation conditions take a tu rn for the worse later in the year !!!
Don't forget to send your comments about today's program, radio hobby related questions and QSL requests to arnie@rhc.cu of VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba... hope to have listening to our mid week edition of Dxers Unlimited next Tuesday and Wednesday UTC days...