domingo, 5 de julio de 2009

Radio Havana Cuba - Dxers Unlimited's weekend edition 4-5 July 2009‏

Sunday, July 5, 2009
By Arnie Coro Radio amateur CO2KK

Hi amigos radioaficionados around the world and also in Earth orbit.

I am Arnie Coro,radio amateur CO2KK, your host here at RHC´s twice weekly radio hobby program.

Now here is item one: New solar activity showing up...

It is from solar cycle 24, and the sunspot active region is already generating flares as it continues to develop at a very fast pace. But it would take at least one more day before we see the effects of sunspot active region 1024 amigos !. The optical sunspot count is now at 17, and it may move upward during the rest of the weekend.

At the request of Dxers Unlimited listeners that experienced difficulties picking up the mid week edition of the program due to the very low ionospheric activity ...

Here are some parts of that show, repeated here today during our weekend edition.

All the world´s ionospheric vertical incidence sounders are,registering a very weak ionosphere, due to the very low free electrons count per cubic centimeter, that is the yardstick used by scientists to measure ionization. Maximum useable frequencies at the peak times are not exceeding more than 25 megaHertz, and then this is happening for very short periods of time. It would take a significant increase in solar activity to improve HF propagation by means of the NORMAL ionosphere layers.

So, if you happen to pick up DX signals on frequencies above 25 megaHertz, , or are able to listen to very short skip on the 20 and 15 meters amateur bands, you can be sure that they are reaching you via the Sporadic E clouds that are typical of this time of the year and that have nothing to do with solar activity.

Item two: this one is also from the mid week edition that went on the air and on the WEB on Tuesday and Wednesday UTC days...

From time to time the world receives news about a sensational new antenna system … it happens over and over, only to end up to be yet another scam to funnel money into the pockets of bandits, or in the best case, the claims for the ultra miniature antennas with the efficiency of a huge rhombic or curtain array may come from someone that , although honest may be absolutely ignorant of electromagnetic wave theory…

Once again we are hearing about what looks like yet another case of impossible performance claims...This seems to be the case with a Swiss invention, quote , unquote on the word invention, that goes under the name of the ROOMCAP antenna, whose inventor claims that the 1.5 meters long piece of metal and a coil is capable of replacing a full size half wave dipole antenna on the lower frequency amateur bands.

The inventor, again quote, unquote on the word inventor, refuses to provide information about his antenna, and is requesting one hundred dollars to be paid to him for a compact disc with the instructions on how to build his ROOMCAP magic antenna…

Before he was banned from several of the amateur radio and antennas Internet e mail lists he was posting messages with his supposedly magic antennas , asking list members to visit a web site where he is showing the latest test of his antenna , something I did at once, only to find that the antenna test is a comparison between a two wavelengths horizontal loop and the very short 1.5 meters long ROOMCAP placed on the roof of a small car…

And amigos, that is like comparing apples and oranges, because the Swiss inventor is ignoring the standard procedure to field Test HF antennas that calls for installing not one but two reference antenna systems, a quarter wave vertical monopole over a ground screen of 120 quarter wave radials, and a vertical half wave dipole, with the lower branch of the dipole at a quarter wavelength above the ground, and fed with a transmission line that must leave the center of the elevated vertical dipole at a 90 degrees angle …

So amigos, be aware that false claims about small HF antenna´s performance are constantly appearing , especially now that it is so easy to create a website and fill it with what best could be described as rubbish…

More radio hobby related items coming up in a few seconds when the mid week edition of Dxers Unlimited continues in just a few seconds… I am Arnie Coro in Havana

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Si amigos, you are listening to Radio Havana Cuba´s Dxers Unlimited radio hobby program and now here is item three our technical topics section that will be dealing a bit more about simple homebrew radios, the ones that you can show with pride to family and friends while bringing in loud and clear several of the world´s international broadcast stations.

I remember a few years ago , when a friend visited my shack and left with a small plastic bag full of electronic components and two circuit diagrams that I had drawn for him.

Two days later he calls me on the phone and says… Coro, listen to this, and sure, I was able to hear our own Radio Havana Cuba's Spanish language program over the phone line… Amigo Carlos then said that what I was hearing was coming out of the radio he had just completed to build following the first of the two circuit diagrams he had taken home . That radio receiver was picking up our 12000 kiloHertz transmission from the Bauta transmitting center with just a one meter long wire antenna attached to it.

Carlos then told me that the regeneration control was working very smoothly and that he was able to pick a popular amateur radio morning round table on 40 meters by advancing the regeneration control until the single side band signals were received clearly.

Now listen to this: the circuit diagram of that radio uses just four active devices, draws very little current from the power supply and can be built into a very small box. The three transistors used are common NPN type signal devices that Carlos recycled from a TV set, and the integrated circuit audio amplifier was the LM380 IC I gave him.

Carlos told me that he had wound several coils, and that so far he was able to pick up stations from the low end of the AM broadcast band up to the 19 meters or 15 megaHertz international short wave broadcast band.

He then asked about the possibility of switching the coils , so I started to look into my parts bins to see if I could find a dual pole three, four or five positions wafer switch, and fortunately my search was rewarded with the finding of a very nice looking ceramic wafer switch, two poles and five positions that Carlos has already put to good use in a second radio he has built…

He has left the first experimental receiver that was mounted on a small piece of half inch plywood, as a demonstration project to be taken to our next radio club meeting, as there are many other club members interested in home brewing simple receivers… Carlos and I talked about the tools that he had used to build the two radios, and he said all he needed to homebrew the radios where a 30 Watts soldering iron, a set of long nose pliers, a side cutter plier and a small screwdrivers set, plus his digital multi meter .

Carlos knows how to identify the different electronic components very well, and he also is good at following a circuit diagram, two very important elements that are essential requirements if you want to start homebrewing radios.

Si amigos, yes my friends, oui mes amis, developing your skills to homebrew radio equipment is one of the 84 ways of enjoying this wonderful hobby , yours and mine: RADIO… …..

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QSL on the air, YES, QSL on the air to Dxers Unlimited´s listeners that have requested the Polyakov simple short wave Receiver circuit diagram… I now have ready here a small text file with more information about that very simple circuit , that uses just two signal diodes , a transistor injection oscillator and a two transistors audio amplifier …

Of course amigos Jules and Sarah that you can add an integrated circuit audio amplifier following the two transistors of the receiver´s audio stage, and that will bring up the set´s volume to room filling levels…

But, you will need more current from the power supply, so the batteries will last much less than when they are feeding just the three transistors of the original receiver design.

Answering a question sent by amigo Edward from the UK, I must emphasize that the Polyakov detector is not your best option for listening to AM stations , because you must keep the frequency of the injection oscillator within just a few cycles per second from the AM station´s carrier frequency or otherwise your audio will show a sort of growling sound that is very annoying.

Do remember that the Polyakov detector requires that the local injection oscillator operates at half the receiver´s frequency , something that is very useful as it is easier to make oscillators more stable when they operate on lower frequencies.

As a matter of factI have used the Polyakov antiparallel diodes mixer,that by the way is the correct name of the circuit, to down convert a 2 point two GigaHertz signal to a 144 megaHertz IF, and it worked very well also in this particular application.

When used as a product detector you actually have two main frequencies at the output, and one of them is, of course, the audio from the station you want to hear !!!.

As compared with a four diode double balanced product detector, the Polyakov twin antiparallel diodes product detector has several advantages, and one of them is the fact that the injection oscillator frequency is operated at half of the signal frequency…

For those of you that have not yet sent a request for the dot pdf file of the ultra simple 40 meters amateur band Polyakov detector receiver, let me remind that the e-mail address to send your request to is inforhc@enet.cu, again slowly and using the phonetic alphabet… inforhc@enet.cu... It is a very small size computer file that is sent as an e-mail attachment, as a matter of fact it is only 32 kilobytes of data so it will be downloaded just after pushing the download key of your computer.

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Just to complete the information about the easy to homebrew Polyakov detector receiver for the amateur bands, let me add that a 30 meters band version requires the use of a five megaHertz variable frequency oscillator, that at the same time provides an excellent calibration mark, because you only need to zero beat the five megaHertz injection oscillator to any time and frequency standard station that uses this frequency or also 10, 15 and 20 megaHertz. The amateur 30 meters band starts at 10.1 megaHertz and it is a digital modes only ham band, in other words you won´t hear any phone stations from 10.1 to 10.150 megaHertz, or at least you should not hear any voice signals there, although from time to time illegal stations do use that range of frequencies for their outlaw activities…

The ultra simple receiver uses a one transistor variable frequency injection oscillator, but a more sophisticated , and of course more complicated version uses a classic three transistors VFO or variable frequency oscillator, that is made of a Colpìtts oscillator stage, followed by a two transistors buffer for optimum isolation.

Using a field effect transistor for the oscillator stage increases both long term stability and makes the circuit less sensitive to small voltage and temperature variations, because the FET or field effect transistors are high impedance devices that provide much better performance than bipolar transistors when used in oscillator circuits.

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ASK ARNIE , si ASK ARNIE, yes ASK ARNIE is the most popular section of this program, and Dxers Unlimited listeners from all around the world send their questions that when answered here have made possible for many other listeners to learn more about radio and solve some practical problems too.

Today´s question sent by Mathias from Bremen in Germany is typical of type of request I get here every day, Mathias wants to know what would be the best amateur band or bands to set up at his soon to be on the air ham radio station, and he adds, Arnie , of course that I am looking for your answer regarding the relation between the present phase of the solar cycles and what may be or may not be worthwhile .

Well amigo Mathias, it is clear now that solar cycle is over , and that we have a very slow start up of cycle 24that may extend for a period even as long as a year more, and solar activity is going to remain within effective sunspot numbers that won´t go higher than 20 units or 30 units…

Under such circumstances, my advice is that whatever resources you are going to invest on your ham radio station, should go to antenna systems from 160 meters to 20 meters.. You will find that most of the time , at this phase of the solar cycle 24 , frequencies above 18 megaHertz will simply won´t propagate trough the ionosphere most of the time … But, from time to time, as for example during the summer months you may hear some activity on 12 and 10 meters via sporadic E skip….

Amigo Mathias , if your budget is limited try installing a 40 meters band half wave dipole as high and as in the clear as possible, and add to it a pair of twenty meters band elements, so that you will end up with an effective three bands antenna…

The 40 meters band dipole, the 20 meters band dipole that are both half wavelength resonant antennas and then your 40 meters band antenna will also perform quite nicely as a three half waves center fed system on the

15 meters band. If you are planning to use , as you explain in your e-mail a modern high tech solid state transceiver with a built in automatic antenna tuner, feeding the above mentioned antenna with 50 ohms coaxial cable via a one to one balun will allow you to enjoy amateur radio during the next two years or so, and allow enough time for the future installation of a rotatable multiband Yagi antenna that will provide optimum performance during the peak years of the new solar cycle.

And now as always at the end of the show here is Arnie Coro´s Dxers Unlimited´s HF plus low band VHF propagation update and forecast for this weekend and the first three days of next week…The chain of zero sunspots count was broken by the sudden outburst of a new active region, number 1024 that scientists affirm belongs to new solar cycle 24. It is growing at a fast pace, and it may signal the long awaited start up of cycle 24 as we were all expected it to happened.

Happily a lot of sporadic E skip all over the northern hemisphere, with the maximum useable frequency curve moving some days well past the FM broadcast band...

The E skip openings have included great double, triple and even four hops propagation events…

See you next Tuesday and Wednesday UTC days at the weekend edition of the program amigos… !!!

Posted by Arnaldo Coro at 9:16 AM

via Yimber Gaviria, Noticias de la Radio
http://yimber-gaviria.blogspot.com

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