Wednesday, August 20, 2008

DXers Unlimited - weekend edition Aug 16-17

Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited's weekend edition for 16-17 August 2008
By Arnie Coro CO2KK

Hi mis amigos radioaficionados around the world! This is the weekend edition of your favorite radio hobby program, the one and only that really attempts to cover every single aspect of this wonderful way to enjoy your spare time : RADIO... and when I say RADIO, I mean every single aspect of our hobby that involves in tne way or the other electromagnetic waves... from monitoring the mysterious sporadic E band openings that extend well up into the VHF region of the radio spectrum to the so called natural radio signals, the whistlers that are extra long wave Planet Earth´s own natural radio "noise". We can also detect planet Jupiter's powerful radio signals with a simple homebrew radiotelescope, and yes that´s something that can be done with a very easy to install and rather small antenna system and receiving equipment so simple in fact, that picking up Jupiter's radio emissions is surely my favorite radioastronomy demonstration when someone visits my shack at anytime time that Jupiter is above the horizon... The radio signals from Jupiter sound like waves reaching a sandy beach,and you can be sure that the signals are coming from Jupiter by correlating the astronomical data with your radio observations. When Jupiter is below the horizon the signals are not heard, and you start to pick them up when the big planet can be seen from your location

Si amigos, there are at least 84 different ways you can enjoy the radio hobby, and ham radio contests are certainly one of the most challenging of them all.. Now let's start with one of those very attractive ways of enjoying the hobby, that is turning yourself into an amateur solar observer: Following the solar cycle on a day to day or even hour by hour schedule is, and I warn you all, certainly addictive... and it is also a very rewarding experience, as you will learn a lot about the complex solar-terrestrial relationships that have such a great influence not only on short wave radio propagation, but also in many yet unknown aspects to mankind... Solar cycle gurus will tell you that watching the Sun's activity on a day by day basis is very interesting, and once you master the basics, then you can start making your own propagation analysis that will lead to a much more fruitful enjoyment of whatever time you devote to operate your amateur radio station or your radio listening post...

I have received many requests for HF propagation analysis and forecasts from contest operators in Canada, that were planning to activate the rarely on the air CQ Zone 2, also hams from Germany and the UK have requested a special Arnie Coro contest ropagation guide,that have also been used by several of the most active and rare DX expeditions like one the most succesful Clipperton Island events... The main reasons for such requests for a special contest propagation update are, first of all antenna related, and in second place they are looking for advice on the bands that are more likely to produce the best results during different times of the day...

By the way there are several Internet on line courses that will help you to learn a lot about the solar cycle, and once you master one of them, your capacity to produce accurate and effective HF propagation updates and forecasts will increase significantly...

Item two: Closely linked to item one: Solar activity is at very low levels at this moment, and the effective sunspot number Saturday at 12 UTC was just 2 units, while the mid latitude A index, the geomagnetic disturbance indicator for latitudes below 40 degrees North or so, was at 2 units, so you should expect rather nice propagation on the three tropical bands, 120, 90 and 60 meters plus the AM broadcast band...,but we may soon be under the effects of a high speed solar wind coming from a coronal hole, that will spoil HF propagation still more above 40 degrees North latitude. Due to the very high summer thunderstorms activity, your reception of frequencies from 100 kiloHertz to 6 megaHertz is going to be rather noisy to say the least, and it is expected that the recently formed tropical storm FAY, hovering between Haiti and Cuba at the time you are listening to this program will also act as a big static crashes noise generator because of the thunderstorms associated to the bad weather system.

Item three: ASK ARNIE, la numero uno, the number one most reported section of Dxers Unlimited will follow, after a short break for station ID...

Si amigos ! This is Dxers Unlimited's weekend edition and here is now, as announced, ASK ARNIE, la numero uno, your favorite section of the show, today's question came from several listeners in the USA... they all ask my opinion about power amplifiers for amateur radio stationsthat use MOSFET devices instead of vacuum tubes or bipolar transistors.

MOSFET , is the acronym for Metal Oxide Semiconductor Field Effect Transistor, a technology that has developed at a fast pace during the past five years. The power devices using MOSFET technology are now more rugged and reliable, and what is also important for amateur radio applications, they are becoming less expensive.

Vacuum tubes power amplifiers are still made, and the quality of high power triodes and tetrodes made using the metal to ceramic bonding technologies can best be described as impressive, with the number of service hours achieved going past the ten thousand mark, so, for all practical purposes, ham radio high power linear amplifiers operated under normal conditions will not require replacing the high power tubes for a long time.

But, the fact is that MOSFET amplifiers are gaining in popularity, among other things because they operate at much lower voltages, and the cost of the active devices is going down .

Homebrew amplifiers using MOSFET devices are more difficult to build for the average radio amateur than the equivalent power vacuum tube designs, and some of the parts required for the MOSFET amplifiers are not easy to find, but for the experimentally inclined radio amateur, homebrewing a medium or high power linear for the HF bands should prove to be a challenge that can be met with success.

Among the advantages of the MOSFET amplifiers in the power range from 10 to 100 Watts are that they can be operated with drain voltages not higher than 24 to 28 volts, that lend themselves to the use of modern up to date technology switched mode power supplies that are very efficient and lightweight too.

My answer to the listeners that requested information about the selection of factory built high power amplifiers or new transceivers using MOSFETs or bipolar transistors, is to go to the MOSFET based designs, because they are typically much more rugged than the bipolar transistors, as some of the most recent HF and low band VHF amateur transceivers have clearly demonstrated., si amigos, is my e-mail address where you can send your radio hobby related questions for the ASK ARNIE section of the program, your signal reports and QSL card requests, and also your ideas and suggestions for improving this program... VIA AIR MAIL, send your postcards to Arnie Coro, Radio Havana Cuba, Havana, Cuba... now here is our next item of today's show...

There are now many more radio amateurs in Cuba than ten years ago, our hobby is growing here, and the new ham radio operators have quickly learned how to operate during emergencies. At the moment I am writing the script of this weekend edition of the program ,radio amateurs in the five easternmost provinces of Cuba are getting their stations ready as Tropical Storm FAY is approaching. According to Cuba´s top tropical cyclones expert , ProfessorJose Maria Rubiera, the people living in the eastern provinces should began preparations to deal with heavy rains and tropical storm force winds as the newly formed FAY either makes landfall or passes very near the southern coast of Cuba… Already tropical storm FAY has poured a lot of rain over the Dominican Republic and Haiti, and it is expected to gain more strength when it enters the very warm waters of the Caribbean sea south of Cuba.

As always amateur radio operators provide voluntary emergency communications alternatives , deploying portable stations at remote locations where normal cable and fiber optic phone services may be affected by the storm.

Now, here is the technical topics section of Dxers Unlimited, now ranking as the number three most popular according to listener's correspondence, closely our HF and low band VHF propagation updates and forecasts offered at the end of the program... Today I will tell you about a very simple antenna system for the 2 meters band, that has proven to be very effective during tropical storms and hurricane , as well as other emergencies. It is made with a length of RG58U coaxial cable, but you can make a more rugged version using RG213, or RG8X cables.

This antenna uses a single coaxial connector that is used to connect it to the 2 meter band rig, be it a mobile , a base unit or a handie talkie. The antenna itself is made by removing the outer insulation from the coaxial cable for a certain length, then folding back the shield ofthe cable over itself for a length of 51 centimeters, and leaving the center conductor extending for a length of 49 centimeters. To complete the antenna , you make a coaxial cable choke of 8 turns, that starts its winding at the point where the folded back shield ends… If you have at hand a VHF standing wave ratio meter, then you can make the top end of the antenna a bit longer, and trim its length for minimum standing wave radio at the center of the band… This antenna can be hanged from any available support, and has shown a noticeable gain over a handie talkie´s small antenna, the ones known by hams as rubber duck, because they resemble the tail of a duck. This half wave coaxial dipole can be rolled up for easy transportation, and the fact that it has only one coaxial connector makes it much more reliable than other portable antennas that require insulators at the feed point. My own practical experience is that this antenna is more reliable than the classic J type end fed halfwave dipole made from 300 ohms or 450 ohms transmission line, that requires the coax to be soldered to the twin lead, something that can be the source of trouble , as it has often happened… So follow your amigo Arnie Coro´s advice and homebrew a 2 meters band coaxial cable dipole and keep it ready to provide emergency communications with your amateur radio station whenever needed… Remember that providing emergency communications under the most difficult and challenging circumstances is perhaps the main reason why valuable radio spectrum is allocated worldwide to the amateur radio service !!!

And now that we are talking about emergencies, do remember to include in your emergency communications kit , a line voltage spike protector for your AC power supply, because emergency generators tend to produce very damaging voltage spikes that can kill your equipment if it is not properly protected, nowadays lot of electronic equipment include spike suppresors at the power line input One of the most interesting features of these spike or transient suppressors is that they are designed to fail into a so called heroic failure mode, shorting out the input so that the protecting fuse will blow if the spike reaches the device's preset limit for a certain period of time.

QSL on the air… QSL on the air to amigo Hector in Puerto Rico who sent a very nice e-mail message requesting more information about HF propagation forecasting computer software. I must say that the in my opinion the W6EL HF propagation forecasting program, that is freeware , is certainly the most user friendly, easier to understand and to use of them all…with the added advantage that it will cost you nothing !!! It can be downloaded from several Internet sites and the learning curve is quite fast !!!

So amigo Hector, you can start by downloading and learning how to use the W6EL propagation program, and later on explore other more sophisticated options that are also available.

And now amigos, as always at the end of the show when I am here in Havana, here is our exclusive and not copyrighted, in the public domain, HF propagation update and forecast, together with low band VHF information too. We are still seeing sporadic E openings with some of them reaching the FM broadcast band. Solar flux and sunspot count at rock bottom levels, the flux at only 65 units and ZERO sunspots for many, many consecutive days.The effective sunspot number is an amazingly low TWO, and we are expecting an HF propagation disturbance to begin by Sunday, when a high speed flow of protons from a coronal hole will be reaching the Earth´s magnetosphere… See you all at the mid week edition of the program next Tuesday and Wednesday UTC days, and don´t forget to take a little time to tell me via e-mail what you liked most of this show and any radio hobby related question you may want to ASK ARNIE…
(Source: Arnie Coro/R Havana Cuba)