Sunday, August 26, 2007

DXers Unlimited - August 25-26

Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited’s weekend edition for 25-26 August 2007
By Arnie Coro CO2KK

Hi amigos radioaficionados around the world and in orbiting planet Earth…welcome to the weekend edition of your favorite radio hobby program that you are picking up under rather difficult propagation conditions due to a combination of very low solar activity and the effects of a disturbing high speed solar wind impacting into the Earth’s magnetosphere… But, if you stay up late, your lack of sleep will be rewarded by much better propagation conditions than those prevailing during your local daylight hours, as we are still in the summer, when that happens due to the high temperatures reached by the ionosphere in the sunlit hemisphere… Item two:

Despite the poor propagation there are small windows when somewhat better HF conditions make possible picking up DX stations. For example, Friday morning, while testing my new fan dipole that was provisionally installed at just 3 meters, that’s about 10 feet above my reinforced concrete roof, I tried to check in on the 14245 kilohertz DX net, and despite the high noise level, and also high ionospheric absorption about an hour before local noon, I was able to work a station in California and another one in Arizona, where it was much earlier in the morning, so their reception of my signals was much better.

The twenty meter band was open for short skip from Havana to Northern Florida, possibly via a sporadic E cloud and to the west coast of North America via typical F2 layer propagation. The fan dipole is showing a 1.8 to 1 standing wave ratio, possibly due to its close proximity to ground…The antenna is fed with 50 ohms coaxial cable using a one to one balun, or balanced to unbalanced broadband transformer at the feed point. I would had preferred to feed this antenna with a 350 to 400 ohms impedance open wire balanced line, but this wasn’t possible because the way the open wire line had to be routed into the shack…

Tests at the low height above the roof show that the antenna works between 10 megaHertz and 29.6 megaHertz, something that was expected after modeling the antenna using the Japanese freeware MMANA antenna modeling software…This antenna is also a good performer for listening to international short wave broadcast stations operating on the 31, 25, 22, 19, 16, 13 and 11 meter bands. So my new coaxial cable fed fan dipole provides nice reception on seven of the international shortwave broadcast bands, and the possibility of transmitting and receiving on the 30, 20, 17, 15, 12 and 10 meter amateur bands. Efficiency on 30 meters is down by about maybe 2 dB from a reference dipole, while on the 10 meters band it is up by almost the same 2dB as compared to a half wave dipole cut for the 10 meters band.

This antenna is used with my wide range PI network antenna coupler or tuning unit, which provides a one to one standing wave ratio all over the antenna’s operating range.

Of course those losses are higher with the coaxial cable down lead than with the open wire line, but in actual practice it is difficult to tell the difference between the two feed lines. The antenna is made using six wires of identical length, each exactly 5 meters long… one of them is placed horizontally and the other two spread upwards and downwards from the feed point, so that when they reach the end, they are separated by 1 and a quarter meters from the center horizontal wire…

The name of the antenna is a FAN BROADBAND DIPOLE, and ideally it should be fed with an optimized 350 to 400 ohms open wire transmission line…It is a nice general purpose antenna for amateur radio and short wave listening that can be built at low cost and can be installed when only about 12 meters or horizontal space is available, and even less if you install it as a sloper, that is with the antenna tilted at an angle between 20 and 45 degrees.
Si amigos, yes my friends, oui mes amis, you are listening to the weekend edition of Radio Havana Cuba’s Dxers Unlimited. I am Arnie Coro, radio amateur CO2KK and here is item three of today’s program…more radio experiments with the parts recycled from inside discarded compact fluorescent light bulbs. I have just successfully tested two of the power transistors removed from a lamp that broke down when a friend was cleaning it…

Both transistors tested OK and I already used one to replace the series pass power transistor in an old power supply that was built many years ago. It is used now to power an ancient laptop computer that no longer runs from its battery, and the power transistor was damaged when the two output terminal wires touched with each other causing a short circuit, something that in the case of this very old design of simple DC regulated power supply was not taken into consideration… So, I thought that maybe the transistor removed from the damaged lamp could work there, and sure, it works quite well, as both its voltage and current ratings are well above the requirements of the circuit. Now I have two other similar transistors ready to replace the audio output pair of a friend’s amplifier that was destroyed also by a short circuit of the output terminals!!!

Another possible application of the recycled power transistors removed from the small printed circuit boards inside the compact fluorescent energy saver lamps is as radio frequency amplifiers for low frequency amateur radio transmitters, maybe up to the 80 meters band, but not higher because the transition frequency, that is the frequency at which amplification by the device equals to one, for these transistors is no higher than 20 megaHertz or so…The typical accepted ratio for RF amplifier transistors is that they should have a transition frequency of at least ten times the frequency that they are going to operate as an amplifier.

Sure my friends, just by recycling electronics equipment you will be able to have a nice stock of parts that will cost you nothing and provide a lot of options for building new circuits.
You are listening to Radio Havana Cuba, the name of the show is Dxers Unlimited and I invite you to send your signal reports and comments about this and other Radio Havana Cuba programs to my e-mail address: and VIA AIR MAIL, send your postcards and letters to Arnie Coro, Radio Havana Cuba, and Havana, Cuba…

Now here is our next item… its la numero uno, the most popular section of Dxers Unlimited… YOU HAVE QUESTIONS, and Arnie answers them… Today’s question was sent by listener
Randolph from Vancouver, Canada. Randy as he signs his e-mail tells me that he listens to our 6000 kilohertz program from 05 to 07 hours UTC, but he says that he is also able to pick our 11760 kilohertz English broadcast during his local early afternoon hours. Randy wants to know if would be possible to make a compact antenna for the 6000 kilohertz frequency because he calculated the size of a half wave dipole and came up with a total length of 23.83 meters that is a bit more than 78 feet, and he says that there is not enough space available for such a long
antenna at his QTH.

Well amigo Randy, you can make a much shorter antenna and still have it resonate on 6.000 megaHertz, something easily achieved with the use of two loading coils that are inserted at points halfway between each leg of the dipole. I have already sent you a very easy to work with computer program that will allow you to calculate how to build your two coils, using easily available materials. Many radio amateurs around the world use such compact inductively loaded antennas, especially popular among the designers of Yagi type beam antennas capable of working on the three most popular higher frequency ham bands, 20, 15 and 10 meters. Those Yagi beam antennas use four coils on each element, that are part of wave traps used to isolate part of the antenna so that it will operate on three bands. Amigo Randy, you can also add another pair of wire element in pararell with the main six megaHertz band antenna, so a nice combination dual band or tri band antenna can be built at very low cost, and let me tell you that these antennas are pretty effective.

AH… before I forget… if you want to resonate the antenna exactly to a center operating frequency, then you will need at least an instrument known as a grid dip meter , in order to be able to actually measure the frequency at which the antenna resonates, after you install the two loading coils. My experience with the software program I use to calculate the coils is that it produces very accurate results, but if you really want to have the antenna tuned to an exact frequency of resonance, then the use of at least a grid dip meter is essential.
This is the weekend edition of Dxers Unlimited and here is item five … DX tips for radio amateurs, that can make very good use of them if you happen to live in North America and the Caribbean and do stay awake well into the late evening… Yes, these tips are particularly effective starting at around midnight your local time, I repeat if you live anywhere in North America and the Caribbean…

Propagation along the darkness path to your west and southwest will provide some nice contacts for radio amateurs and possibilities of monitoring for short wave listeners into Australia, New Zealand, Japan and many of the Pacific islands. Several high power broadcast transmitting stations will provide nice “beacons” to tell you how the band conditions are behaving at any given moment. Transmitters in the Philippines, Australia, New Zealand, Japan, South Korea equipped with big antennas will be the first ones to be heard and the last ones to fade out, while lower power amateur radio stations will be start to be heard when the opening improves and disappear when propagation starts to drop…

At this time of the year and stage of the solar cycle, it is certainly nice to stay up late, because your chances of working or hearing DX increase many times as compared to daytime operation.

And now amigos as always at the end of the show, here is Arnie Coro’s Dxers' Unlimited’s propagation update and forecast… Just one sunspot group and it is certainly a small and of simple structure, so the daily sunspot number is the rock bottom 12, a bit higher than during the previous several days with zero sunspot count. The proton density of the solar wind has increased quite a bit, and that may trigger geomagnetic disturbances at high latitudes. The general description for short wave propagation conditions can be resumed with one single word: POOR, because of the combination of very low solar activity and the incoming high speed solar wind with high proton density…

Don’t expect Sporadic E openings, because the season has now, for all practical purposes arrived to its end… Tune in for the mid week edition of Dxers Unlimited next Tuesday and Wednesday UTC days amigos, and don’t forget to send your signal reports, comments about the show and radio hobby related questions to or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba.