Friday, January 21, 2011

DXers Unlimited mid-week ediiton, Jan 18-19

A new edition of DXers Unlimited which includes Arnie's opinion on the present state of the DRM (Digital Radio Mondial) system for shortwave broadcasting. Thanks to Arnie for sharing this with our blog readers.
Gayle Van Horn

Radio Havana Cuba
Dxers Unlimited
Dxers Unlimited's mid week edition for 18-19 January 2011
By Arnie Coro
radio amateur CO2KK

Hi amigos radioaficionados all around the world ! Welcome to the mid week edition of Dxers Unlimited... I am your host, Arnie Coro, radio amateur CO2KK and here is item one of today 's show...A quiet Sun … solar flux hovering just above 80 units, as solar cycle 24 continues to lay dormant despite the fact that it is now officially a two years old cycle !!!

Item two; More about what can now be described properly as the ill-fated digital short wave broadcasting mode... DRM, Digital Radio Mondiale, a fiasco by all standards, because there are no receivers available to pick up those digital broadcasts. DRM has not won the public 's acceptance although it has technical advantages over the classic amplitude modulated, double side band plus full carrier transmissions.

Several years ago, I had the opportunity to exchange points of view with several persons involved in the development of the Digital Radio Mondiale or DRM for short wave broadcasting, and unfortunately they did not listened to people like yours truly, that warned them of the fact that DRM for international broadcasting was not winning the prospective audience for a long list of reasons, among them the most basic one of them all: It was four years ago impossible to buy a receiver to pick up DRM broadcasts at a reasonable price, and today a radio that will allow reception of DRM on the HF bands is still not available. Let me clarify that I am talking about a receiver that may be sold at the same price, or even a slightly higher price than what is normally asked for those medium priced radios that are the ones that sell best among short wave listeners.

In my opinion the stations that are still broadcasting their short wave transmissions using the DRM modulation technology are simply wasting their money, they are dilapidating their budget and add to that the fact that they are also polluting planet Earth, because there is absolutely no reason to run a high power transmitter with DRM when practically no one is listening !!!

Add to that the annoying, the most annoying problem with the present DRM technology, that consists of total audio cuts when the signal levels have to deal with a deep fade. In contrast with the classic AM that gently fades in and out, DRM signals just vannish, producing that very annoying total silence, that later is replaced with clear audio … So far the software used does not incorporate the possibility of a high degree of redundancy that could certainly deal with the more or less frequent periods of total silence when the signals fade .

DRM for both the medium wave broadcast band and the FM bands is another story, because ground wave propagation in the case of AM is a much more rugged propagation mode, but FM has the multipath problem with all its negative effects.

As the number of international broadcast stations continues into a downward trend, and the budgets assigned to many of them, except perhaps those involved in religious propaganda transmissions, is reduced, it is quite clear that DRM , Digital Radio Mondiale for short wave broadcasting has totally failed, and the probability of recovery are , if any, very slim.

Stay tuned for more radio hobby related information coming from Havana.
I am your host Arnie Coro, radio amateur CO2KK back in a few seconds after a really short break for station ID purposes....

You are listening to Radio Havana Cuba, this is the mid week edition of Dxers Unlimited, our twice weekly radio hobby program … Now here is item three of today 's show. I have received a large number of requests about the 40 meters direct conversion receivers circuit diagrams offered to those interested in building a simple, yet very effective radio receiver that tunes from 7000 to 7300 kiloHertz, but that can have its tuning range extended up to 7500 if you have a special interest in monitoring the 41 meters international short wave broadcast band that is now starting at 7200 kiloHertz, because the International Telecommunications Union decided at a Conference to grant amateur radio users the frequency segment between 7000 to 7200 kiloHertz on a worldwide basis.

Once again this has proven to be a very well thought decision by spectrum policy makers, because amateurs have used the new segment granted to them in Regions I and III as a very effective area to handle much needed emergency communications. Previous to that decision that became effective in 2009, the Regions I and III amateur radio operators could only use the narrow 100 kiloHertz band between 7000 to 7100 kiloHertz, where all communications modes had to make their way through high levels of interference, especially between 7030 and 7100 kiloHertz. After the implementation of the new 40 meters band , spanning from 7000 to 7200 kiloHertz worldwide, communications have become a lot easier because single side band operators are making a very effective use of the newly available to them 7100 to 7200 segment of the band.

Now going back to the simple direct conversion, Polyakov harmonic detector receiver circuit diagrams, let me add that the original version was designed for headphones use, in order to make it a very effective emergency communications receiver that could operate for long periods on battery power. But, you can certainly add a single integrated circuit audio amplifier module, to boost the volume to loudspeaker level, although at the price of having to add a line operated power supply or use much larger batteries.

There are many tips available regarding this receiver ' s family, including the use of a much more elaborate variable frequency oscillator and of audio filters for optimizing CW Morse Code radiotelegraphy and single side band and AM mode voice modulated signals.

The barebones version of the receiver can be put together in a single working session, if you wind the coils before starting to solder the parts. I have used the isolated circuit boards glued to a printed circuit board backplane to assemble several of these radios, but now, thanks to a local radio amateur friend who is an excellent draftsman, we have a printed circuit board layout that when totally assembled gives the radio the looks of a professional job !!!

You can learn more about simple Polyakov harmonic detector receivers by sending an e'mail to inforhc at enet dot cu... Again , inforhc at enet dot cu !

Feedback from listeners reached me every day, via e'mail and also on the amateur bands, whenever I have the time available to go on the air and work a few stations. One of my favorite spots is on the 20 meters band, on 14 060 kilohertz that has become a nice meeting place for QRP or low power ham operators from all around the world. When propagation conditions are above average, it is quite normal to be able to work stations running 5 watts and even lower power transmitters that are operating from Europe and Africa. But reaching Asia requires exceptional propagation, that is only available when the solar flux figures run above the 100 mark for several days. The courtesy and respect that prevails on the 14 060 kiloHertz QRP frequency is really outstanding and to be commended amigos. There you can find operators that send slow CW to really help beginners or old timers that are coming back to the world of the Morse code enthusiasts.

On 14060 you won't find high speed machine sent CW , and it you hear someone sending slowly and making mistakes, be patient, ask for repeats when necessary, and also send slowly when answering. CW, Morse Code hand sent and received by ear radiotelegraphy requires that you concentrate on what you are doing, and after enjoying it for some time, you will find that your operating skills develop spontaneously. But of course that you can also do your homework and practice with the aid of a computer.

There are several excellent freeware programs that can be downloaded from websites that offer them free of charge, as a contribution to the development of amateur radio. There are two such programs that I really like and recommend, one comes from the United Kingdom, it is known as the Koch, or Kilo, Oscar Charlie Echo, the Koch method of learning and them improving your CW Morse code skills, it was written by G4FON … the other program that I also like a lot is interactive... G4FON Koch Trainer is a relatively small download , it is easy to set up and really works very well... The other CW training program that I like a lot is called Morse Machine, and it is also freely available for downloading... Morse Machine is totally interactive, and it really helps to boost the speed of your reception one you have mastered all the 41 characters used by the International Morse Code...
(Arnie Coro/Radio Havana Cuba)