Radio Havana Cuba

Dxers Unlimited

Dxers Unlimited's weekend edition for 6-7 February 2010

By Arnie Coro

radio amateur CO2KK

Hi amigos radioaficionados around the world... this is the weekend edition of your favorite radio hobby program ..

I am Arnie Coro, your host here in Havana... as always it is really nice to share with you about seventeen minutes of on the air and on the world wide web time.

Here is now item one: The Sun is waking up.... we are seeing now three active sunspot regions on the solar disk, and satellites keeping watch on the other side of the Sun are showing even more sunspots there too...

This upsurge in solar activity forms part of what is known among radio engineers and hobby enthusiasts as the solar cycle, but a more proper name for it would be “the solar magnetic activity cycle...

This cyclical activity of our nearest star is the main source of a periodic variation in the energy sent towards the Earth by the Sun, something which drives variations in the space weather, and also, to a certain extent produces changes of the weather on the ground.

According to weather records, at least one extended period of a very quiet Sun was the cause of what is known among meteorologists as “ The Little Ice Age ”, that turned areas of Europe into practically polar regions.

Scientists follow the solar cycle by means of carefully counting the frequency and placement of the sunspots that are visible on the Sun.

During the year 2009, the Sun was spotless for a bit more than 70 percent of the days, a total of 260 days to be precise, and that was the tail end of solar cycle 23... one of the longest ever recorded.
As a matter of fact,the Sun had not been so quiet since early into the 20th Century... In other words, we have just witnessed the quietest Sun for almost one hundred years.

But, right now, as you listen to this program via short wave or are picking up the audio from our streaming audio via Internet, the Sun has waken up ! Solar optical observations Saturday , February 6 , are showing three active sunspot regions... something that had not happened since May of 2008...

Scientists are now also equipped with a new tool for looking at the Sun.... satellites that are located orbiting the Sun in positions or orbital slots that make possible to constantly monitor solar activity practically all around the Sun.... something that is changing our capacity to provide short term solar activity forecasts.

Si amigos, yes my friends, oui mes amis.... The sunspots are coming back, and as soon as we see a monthly average above 20, or an average solar flux for the last week above 90 units, you can be sure that short wave propagation conditions are going to be a lot better, with a return of DX on frequencies above 15 megaHertz !

Item two: Compact fluorescent lightbulbs electronic circuit boards are a treasure chest of parts that can be easily recycled and used to make some really nice little radios...

For some time now I have worked together with several other radio hobby enthusiasts on the design , assembling and testing receivers that were built using mostly recycled components recovered from the Compact Fluorescent light bulbs circuit boards...

As we were advancing in the testing of the transistors used as the switching elements on the CFL's we found out that their cut off frequency was rather low... placing a clear limit to the higher frequency band that our radios will be able to operate.

So far, we are able to make those transistors oscillate reliably up to around four megaHertz, making possible to build variable frequency oscillators that operate on the 80 meters amateur band... Using the amazing Polyakov harmonic two diodes mixer, combined with the CFL transistors , we have achieved now a landmark...

It is a 40 meters band direct conversion receiver that uses four transistors recycled from the CFL's, one as the variable frequency oscillator operating at half the received frequency, as required by the Polyakov mixer, and three transistors forming part of the high gain audio amplifier that follows the product detector.

The prototype receiver uses a front end bandpass input filter built around coils wound on small segments of PVC pipe or empty pill bottles...so there is no need to use ferrite or pulverized iron toroid cores.

The project is about to be completed, and we will soon have to sit down and write the detailed, step by step instructions that will make possible assembling the radios, that so far have proven to work very well on the 160, 80 and now also on the 40 meters band...

By using three additional high frequency capable NPN or FET transistors, that can not be found on the lightbulbs circuit boards, the receiver can be made to operate on frequencies up to the 50 megaHertz or 6 meters band, and that is another option that is also in our plans to explore in the near future...

Item three: A lot of fun at our Radio Club's recent meeting, when I took with me the prototype of the two meters band “ FANTENNA”, made by using a discarded electric fan protective mask for the ground plane of a 120 degrees electrical height vertical antenna....

Earlier during the week, I received the visit of a group of radio amateurs from the Guines Radio Club, who came to see a demonstration of the FANTENNA that was going to take place from my second floor open terrace.

The antenna testing session took place around noon on Thursday, and what we did was to compare how the FANTENNA and a standard factory built helically wound short vertical antenna worked. The short vertical , known among radio amateurs as the “rubber duck ” , because it resembles the wagging tail of a duck, is known in Spanish as “ la gomita” , or the “ little piece of rubber”... and it comes as the de facto standard antenna system for the 2 meters band hand held FM transceivers or handie-talkies...

What we found out during our comparative tests was really impacting... Using the FANTENNA, connected to the FM handie talkie with a short length of 50 ohms coaxial cable type RG58U, we could access and establish perfect communications by way of the Salon mountain top repeater, located about 50 miles away from Havana...

We even made several nice two way contacts with stations located on the Cuban archipelago second largest island, the Isle of Youth, that are able to reach the Salon mountain repeater across the Gulf of Batabano...

Then we reconnected the rubber duck antenna and tried to access the repeater with it... we even moved around to try to find a sweet spot, a trick that 2 meter band operators learn after some time operating on that band... well, we finally found a place right at the balcony rail were we could hear the 145.110 repeater better, and even could access it, but the reports received from other radio amateurs said that the signal from CO2KK was very poor and masked by a high noise level...

Switching back to the FANTENNA, the other stations reported that we had again a clear signal , with perfect Q5 copy !!!

The group of hams from the Guines Radio Club quickly took notes on the details of how to build the FANTENNA, and as expected asked me why the vertical element was much longer than the standard quarter wave whip .

I explained that according to antenna theory, as verified by using a well known antenna modelling software known as MMANA-GAL, the 120 electrical degrees high vertical had more gain than the quarter wave antenna, and also, the vertical radiation pattern concentrated more energy near to the horizon, a great advantage when you want to communicate with ground and ground mobile stations. Jorge, CM3JAM, the President of the Guines Radio Club in La Habana province, went home with his group promising to put on the air several FANTENNAS very soon.

By the way, matching the 120 degrees or one third of a wavelength vertical radiating element is done very easily with a small length of coaxial cable that is used to cancel the antenna's inductive reactance....Using this ultra simple matching system, we achieve a one to one standing wave ratio after spending some time experimenting with the length of the coaxial cable series capacitor...

Now, let me add that the diameter of the electric fan's protective mask or cover should be no less than 15 inches for best results, although I had at hand a 12 inches diameter one and it worked OK too, after spending a few minutes with the SWR meter pruning the length of the coaxial cable matching capacitor.

Technnically speaking, the FANTENNA is a 120 degrees high radiator working into a ground plane... that is formed by the many metal wire spokes of the fan protective mask... It is certainly a very low cost approach to building a 2 meters band antenna for FM communications, and as one of the visitors from Guines told me, it is also a very nice club project too. Stanby now for a few seconds, as we proceed to a short break for station ID amigos, I am Arnie Coro, CO2KK

…...............

This is Radio Havana Cuba, the name of the show is Dxers Unlimited and here is now item four of today's program... a last minute update about the FANTENNA... known is Spanish as “ Antena Ventilador ” You have just heard about how this antenna has a low take off angle... and that is a very nice feature for working the low earth orbit or LEO amateur radio satellites... and also the International Space Station too.

If you figure out the cost of Arnie Coro's FANTENNA, you can confirm once again that amateur radio is a hobby that we all can enjoy on a shoestring budget !!!

My prototype FANTENNA required three meters or about 10 feet of RG58U very flexible coaxial cable, a BNC male connector, a 65 centimeters length of 10 millimeters diameter aluminum tubing, and a 15 inches or 38 centimeters diameter fan protective mask recycled from a burned out desktop fan !!! I also had to prepare a short length of RG58U used for the reactance cancelling matching capacitor …

I used an aluminum plate disk that was placed at the center of the fan protective cover to locate there an insulator to which the vertical element is attached. Total time spent in assembling the prototype was about two hours, but now they can be made in less than an hour after we learned the “ optimum how to ” of the assembly process...

Amigos, its already time for our exclusive and not copyrighted HF propagation update and forecast, that includes when required a VHF update too.

Solar activity is moving up, three active sunspot regions now clearly seen , with two of them still to be named, solar flux should be reaching 85 units pretty soon... Expect possible higher latitudes propagation disturbances at the beginning of next week …