By Arnie Coro
radio amateur CO2KK
Hi amigos radioaficionados… listening via short wave and also by means of our streaming audio from http://www.radiohc.cu. I am your host Arnie Coro, radio amateur CO2KK now ready to start the middle of the week edition of your favorite radio hobby program…
Here is item one… As anyone monitoring the HF bands will easily find out, the low solar activity continues to limit the chances of short wave propagation on frequencies above 15megaHertz, even during the best times of the day at any given location.The exception comes when sporadic E layer openings move the maximum usable frequency up past the 25megaHertz range.
Observations confirm that solar cycle 24 continues to show very weak activity as compared with any of the previous 5 solar cycles. As a matter of fact today Tuesday July 17 we have seen so far twenty consecutive days without sunspots…
Item two: You have questions and I do my best to answer them… Yes amigos, every day the e’mail brings in most interesting questions from listeners all around the world… Like for example the one sent by Manuel from Mexico City, who listens regularly to our 15140 kiloHertz frequency.
Manuel is asking why it is not possible for him in Mexico city to pick up short wave stations from other countries in the Americas besides Cuba, Brazil and his local Radio Educación that he receives via the ground wave signal.
Well amigo Manuel, first of all, let me tell you that at this moment there are few stations on the air on the short wave bands with high enough power to be heard on a regular basis… Venezuela was in the process of installing its first international broadcasting transmitting station, but that project is now at a standstill. And to answer the other part of your question, I will be back in a few seconds after a short break for station ID. I am your host Arnie Coro in sunny Havana, Cuba…
This is Radio Havana Cuba, the name of the show is Dxers Unlimited, and yes amigos, we do QSL, we do send QSL cards to listeners that report our programs, and this is done absolutely free of charge… Now part two of the answer to amigo Manuel, who lives just outside Mexico City.
Besides Radio Havana Cuba, that can be picked up using a rather simple short wave receiving antenna, you may be able also to pick up several stations from Brazil, as well as maybe Peru and Bolivia, are also on the air, especially on the 60, 49 and 31 meters bands, but most of them are using low power and simple low cost antenna systems because they are intended to provide local or regional coverage.
When HF bands propagation conditions are good, you may pick up several of those low power stations from Peru, Bolivia, Ecuador, Colombia and Mexico… reception of those low power short wave broadcasts, mainly on the 60 and 49meters band and also at times on 31 meters…. this will usually take place very late in the evening your local time or just before local sunrise.
For both short wave listeners and amateur radio operators that live in urban areas the installation of an adequate antenna for obtaining best results within the frequency range from 3.5 to 29.7 megaHertz is quite a challenge to say the least. City dwelllers, and especially those who live in apartment building face a great challenge when trying to listen or to operate on the 80 to10 meters ham bands, because of the severe restrictions imposed nowadays regarding the installation of external antennas on any type of building and the extremely high local noise levels.
The rooftops of high rise apartment buildings are an ideal location for VHF, UHF and Microwave operation if you happen to be living at one of the top floors, but are quite useless for that purpose if your apartment is located close to the ground requiring the installation of a very long length of transmission line needed to reach a rooftop antenna and this, if you are fortunate to obtain permission to install it by the building managers.
But, despite all those difficulties, I very often come across a ham radio operator that with a lot of ingenuity manages to operate, for example, on the 20, 17, 15 and 10 meters bands, using different types of compact antennas.
Fortunately the 12 and 10 meters HF bands require a much smaller size of antennas small enough to make them fit across a balcony rail … But 20, 17 and 15 meters are certainly the most popular DX bands when propagation conditions are let’s say, normal or slightly above normal, and that is why people living in housing facilities with severe restrictions as regards to the installation of external antennas try in the first place to put up an antenna system that can be tuned to 20, 17 and 15 meters.
One of the regular Dxers Unlimited’s listeners, who is also an avid ham radio operator, asked about what could be done to install an antenna for the 20, 17 and 15 meters band that could fit into his apartment’s balcony that measured from one end to the other is roughly 5 meters or about sixteen and a half feet. That is just enough to install a dual band 12 and 10 meters fan dipole . His already in use 12 and 10 meters fan dipole has brought some local contacts, and also some DX when the band is open, but as everyone now is fully aware, the 10 meter band openings via the F2 layer are going to become very rare indeed due to the lack of solar activity. Remember what I said at the opening of today’s program , 20 consecutive days without sunspots….
Besides buying an expensive professional magnetic loop antenna with remote tuning, there is another option for our listeners who want to operate on the 20, 17 and 15 meters band.
Go ahead and build a compact short dipole antenna using two easy to make loading coils and two end loading capacitive hats, that will make possible to operate on the 20, 17 and 15 meters bands with rather good efficiency, and also on the 30 meters band with somewhat reduced performance. You must use a balun or balanced to unbalanced, one to one broadband transformer at the feedpoint of the antenna.
The antenna I suggested fits perfectly into a slightly less than 15 feet or five meters of horizontal space, and when fed via factory made or a homebrew one to one balun and using a wide range antenna tuner has proven to provide excellent performance. One good advantage of this antenna is that it can be installed in a couple of minutes when you want to operate or listen to the radio, and likewise it can be taken down and placed in storage at a corner of the balcony !!!
The good efficiency of this antenna design, despite its short length, is due to the use of two carefully built high Q loading coils and the nice looking well designed end loading spiders, that act as an effective capacitive load.
The two loading spiders are built using four wires that are carefully soldered to a circle made of 6 millimeters or about a quarter of an inch copper tubing. Each leg of the antenna is just two and a quarter meters long and they end up connecting to the end loading spiders…The center insulator supports a one to one balun transformer, and the antenna is fed with a short length of RG213 or RG8X coaxial cable that connects it to the antenna tuner.
So far, all our experiments with this antenna have proven that it will work quite well with a simple antenna tuner, making possible to operate on the20, 17 and 15 meters bands, as well as on the12, 10 and even 6meters band too using an antenna tuner.The fact that the antenna is located inside a balcony places some limitations as regards to both the overall coverage and also limits its use to power levels not to exceed 25 watts for safety reasons regarding the exposure to radio frequency energy.
If you want to learn more about this compact antenna system, especially designed for apartment dwellers, just drop me an e’mail to inforhc at enet dot cu, again inforhc at enet dot cu.
And now as always at the end of the show, here is Arnie Coro’s Dxers Unlimited ‘s HF propagation update and forecast. Expect sporadic E openingsto become less and less frequent after the end of July and solar activity continues to be low. The night time maximum useable frequency curve continues to exhibit its usual upward swing that starts after sunset, something typical of the northern hemisphere summer season. Solar flux around 70 to72 units. And please don’t forget to send your signal reports and comments about this and other RHC programs to inforhc at enet dot cu… or via air mail to Arnie Coro , Radio Havana Cuba, Havana Cuba