Radio Habana Cuba: Dxers Unlimited weekend edition for January 13, 2001
By Arnie Coro, radio amateur CO2KK
Hi amigos! Welcome to the weekend edition of your favorite listener-oriented radio hobby program. I am Arnaldo, Arnie, Coro, radio amateur CO2KK... join me for the next sixteen minutes in a tour covering some of the more than 50 ways you and I can enjoy this wonderful hobby....
Here is item one: Well-written, really sophisticated computer software is opening up a new frontier for amateur radio, the detection and use for communications of extremely weak signals...
Item two: Digital TV Dxing now possible in several countries that have already implemented terrestrial digital TV broadcasts, and some very interesting results are found by TV Dxers experimenting with those new signals...
Item three: Want to save time building your own little transistorized regenerative receiver? Then buy yourself a set of amplified computer speakers... they will provide the complete "audio tail end" of your experimental receivers at rather low cost, and you can then use all your spare time to concentrate not on the audio, but on the signal receiving part of your homebrew receiver!!! All it will take is to prepare a shielded audio cable with an appropriate miniplug to connect your receiver board audio output to the amplified speakers' input!!!
Item four: Keyboard to keyboard amateur radio communications is gaining popularity, and no wonder -- so many people nowadays interact with keyboards so much at work that they have become part of our daily lives. So it was natural in my opinion that keyboard communications modes like RTTY and PSK31 would gain in popularity among radio amateur operators worldwide...
Stay right on this short wave frequency for more radio hobby-related information coming to you from Havana...
The name of the show is Dxers Unlimited, we are on the air twice weekly with the most up-to-date short wave plus 50 megahertz band propagation forecasts.
You are tuned to Radio Havana Cuba, and here is Item one in detail: Radio amateurs are making an important contribution to the advancement of radio technology... Sophisticated, well-written computer programs, using the most up to date techniques of audio signal processing with fast machines, are making possible the detection of extremely weak radio signals. In fact detected signals using these Fast Fourier Transform based methods are so weak that they cannot be heard at all using conventional technology... Very slow Morse Code transmissions that send dots that last for 3 full seconds, and dashes that last a full 9 seconds, are now being used on the 136 kiloHertz Low Frequency Amateur Band with absolutely amazing results. And this signal processing technology that uses the computer sound card and specially written software can prove to be a breakthrough for other amateur radio applications also, like Earth Moon Earth communications and the extremely interesting Ionospheric Forward Scatter Propagation Mode....
All it takes to start experimenting with very weak signal reception is a sensitive and stable receiver, a fast computer, and the software -- which is in many cases provided by radio amateurs for free as a goodwill gesture to other amateurs around the world... I ran some weak signal detection experiments Thursday evening, and was amazed of how the carrier from an aviation Non-Directional Beacon, which could not be heard with headphones, showed up very clearly on the computer screen!!!
Now let's jump from the ultrasophisticated technology to a very simple one. Regenerative receivers continue to fascinate radio experimenters worldwide... It is really amazing how even one single transistor can pick up so many stations, and when properly operated receive AM, CW, SSB and even narrow band FM. A few days ago a friend came in with his first regenerative receiver; he wanted to calibrate the dial using one of my digital radios as a reference. He connected his radio to the headphones and we started the process... Then I told him, wait a moment, I want to listen too, so I connected a shielded audio cable to a spare set of amplified computer speakers. "Hey Arnie," he said, "that's a great idea! No need to build the audio output stage; I'll just connect the regenerative receiver's output to a similar set of amplified computer speakers that I already have at home!" After we finished calibrating his radio, something that took us about an hour or so, he went home... The next evening Alberto called me on the phone and made me hear how his amplified regenerative was picking up short wave signals with room-filling volume. See amigos, my friends, mes amis, it is certainly an excellent idea to buy yourself a pair of amplified computer speakers; the ones that have a built-in power supply that connects to the AC power line are better to operate than the ones that use a wall plugged transfomer and DC supply. Amplified computer speakers will provide enough gain for practically any radio project and you will not have to spend time building an audio amplifier, a power supply and connecting to a speaker. SO... you can save time, and use more time to do the actual receiver experiments!!!
BY THE WAY... I tested CM6FG's one-transistor regenerative receiver with my computer's amplified speakers, and reception of AM band broadcast stations was absolutely amazing Thursday evening... I picked up stations from the Eastern part of Cuba, Radio Rebelde on 600 kiloHertz and Radio Victoria on 1050 kiloHertz, Jamaica on 560 kiloHertz, Mexico on 900 kiloHertz and WSB from Atlanta, Georgia on 750 kiloHertz. Reception was excellent, due to a rather low ionospheric absorption index, something that really helps AM Dxing!!!
Amigos, YES, we do QSL one hundred percent here... Just send your signal reports, comments about this show and other Radio Havana Cuba programs to Arnie Coro, Radio Havana Cuba, Havana, Cuba... use Air Mail, and a postcard will do!!! Via e-mail, send your QSL request, signal report, comments about the show and any radio hobby related questions to arnie@radiohc.org, and you will receive the fastest possible reply to your questions, via e-mail and also on the air....
And now let's go to the very popular section of the show, now in its ninth year on the air.. YOU HAVE QUESTIONS and Arnie answers... The question today is from a listener in the USA who wants to know more about digital signal processing for radio reception... Well amigo, that's not a question as such, but I think that it does deserve an answer....
Digital signal processing as we know it today is done essentially at low frequencies; most radios using this technology do all the digital signal processing at a very low intermediate frequency around 12 to 20 kiloHertz; a typical frequency used is 15 kiloHertz. The front end of the receiver is absolutely conventional, as well as the IF or intermediate frequency amplifiers and frequency synthesizers, but once we arrive at the 15 kiloHertz IF, everything is done the digital way. So, as more and more sophisticated extra-large-scale integrated circuits are designed for this purpose, we will see that more and more new receivers will be built using DSP or digital signal processing. Among the many advantages of DSP technology is that you can change a lot of parameters by just writing software!!! Say you want a very narrow filter for extra-weak signal reception, or that you want to experiment with a different Automatic Gain Control time constant... all it will take to implement the changes is adding a few more lines of programming.... and fortunately it seems like at least some digital signal processing receiver manufacturers are making the source code for their radios as open as LINUX, so that everyone can benefit from software written by others!
Now item five of today's weekend edition of Dxers Unlimited...a quick tour of my workbench. This week the workbench is pretty crowded, which is not unusual -- a beautiful old frequency meter is almost ready to be added to my workshop shelf of measuring equipment, and the 586 100 megaHertz computer is still stuck, as I have not been able to find the motherboard's instruction manual yet... the problem is that the onboard serial ports don't seem to work, and when I try to add external to the mainboard, that will also won't work... so the machine cannot be used with the radios, as the computer-to-radio interface works via the serial ports.
Right next to the troublesome computer is my neighbor's cordless telephone that was recently struck by lightning!!! It was a not-too-difficult repair job, and as always, when working with radio gear, I learned something new... This particular cordless phone uses a very interesting frequency-hopping technology!!!
But my pet project nowadays is still very much at the center of the main workbench...it is the single-band amateur band radio that I designed to be built step by step, first providing the newcomer to the hobby with a receiver, which later can be upgraded to a fully operational 10-watt output transceiver!!!
And now amigos, as always at the end of the show, here is Arnie Coro's propagation update and forecast, valid for the frequency range from 3 to 50 megaHertz. First of all, Dxers Unlimited listeners who live at latitudes above about 40 degrees North may witness another session of Aurora Borealis visual displays plus Radio Auroras propagation. This may or may not happen, all depending on how the coronal mass ejection's particles from last Wednesday's solar burst reach the Earth's magnetosphere. The minimum solar activity for this last rotation is now a thing of the past, so from today until around the 17th or 18th of January, solar activity will show a more or less steady increase. But don't expect sensational outbursts of solar flares, although sunspot region 9306 is certainly a very interesting one indeed, that may produce at least a couple of M class flares.
Short wave reception conditions are going to be rather nice during the rest of the week, and amateur radio operators will enjoy excellent DX on the 40 meter band during the local evening hours. The 31 meter international short wave broadcast band, spanning from around 9.4 megaHertz all the way up to very near 10 megaHertz, will be an excellent choice both for regular listening of your favorite broadcasts and for hunting for DX during the late local evening hours. Due to the fact that the solar flux will stay above 170 units for the rest of the month, radio amateurs will enjoy many hours of nice propagation on the 10, 12 and 15 meter bands on an everyday basis!!!
As always, I will be operating CO2KK my amateur radio station on the 10 meter band, using 28.5 megaHertz as my favorite parking spot for both working DX and chatting with Dxers Unlimited's listeners who are also amateur radio operators... And don't forget that your comments about the show are really important to keep Dxers Unlimited as a favorite of people like YOU who enjoy the more than 50 ways that make radio such a great hobby!!!
Arnie Coro CO2KK
Havana, Cuba
January 13, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
To Arnie Coro's Dxers Unlimited
Back to NY Transfer's RHC main page