Dxers Unlimited's weekend edition 23 -24 June 2007
By Arnie Coro
radio amateur CO2KK
Hi amigos radioaficionados worldwide ! Your short wave receiver is now tuned to Radio Havana Cuba's twice weekly radio hobby program, Dxers Unlimited, with yours truly, Arnie Coro at the microphone. Here is item one: Solar activity still way down, with bottom low solar flux measurements of between 65 and 70 units. The sunspot count is ZERO... yes, you heard it right... a totally spotless Sun for the past several days !
Item two: DRM, Digital Radio Mondiale totally stalled, according to the opinion of several prestigious mass media experts, that rightfully have voiced their opinions: they are saying that without the availability of reliable , easy to tune and above all lower priced radios, capable of picking up the DRM short wave broadcasts , the digital transmission system is doomed to failure.
Besides the lack of receivers at a reasonable cost , those who have already experienced DRM reception not at a one day demonstration, but on a regular , daily basis, are telling engineers that the total drop out of the audio output experienced by DRM broadcasts is very annoying to short wave listeners.
For those of you not familiar with DRM, Digital Radio Mondiale, it is a standard specifically created to broadcast digitally, instead of using the classic analog radio modulation technologies, AM and FM that we listen to every day.
Stations broadcasting using DRM have so far, that I know of , not made public audience research statistics or comments by potential listeners, something that in my humble opinion really doesn't help DRM at all, because lack of such information feedback from the potential audience is something to really worry about.
According to several mass media researchers, the pattern followed during the introduction of DRM technology for short wave broadcasting is basically wrong, because low cost radios for DRM reception have not become available yet, and besides that, the promotion of the technology has also been mishandled by the DRM Consortium, who seems to be much more concerned about the engineering problems regarding the transmitters than with the actual reception of the broadcasts, although that seems to be slowly changing now.
More about digital communications modes later , as Dxers Unlimited's weekend edition continues.. I am Arnie Coro in Havana,
Si amigos, yes my friends, I want to ask each and everyone of Dxers Unlimited listeners around the world a single question today... Get ready for writing it down, as I think this is going to be the second open poll about DRM Digital Radio Mondiale.... In a couple of minutes I will be formulating the question, to give you a chance to find paper and a pen or pencil to write it down..
In the meantime let me add that radio amateurs are using digital communications modes with a high degree of reliability and energy efficiency... A keyboard to keyboard narrow band mode, PSK31 is now , at the low ebb of the solar cycle, becoming more and more popular among those amateur radio operators around the world that have learned how to connect their computers to their radios.
PSK31 transmissions running between 10 and 25 Watts power have proved to be extremely effective on the 20 meters ham band, and as recycled computers become cheaper and their availability increases, more and more radio amateurs around the world are learning how to communicate using PSK31....
Now, ready for today's question...Remember, the one about DRM digital broadcasting technology Here we go...
Ready to copy ?
Have you ever listened to Digital Radio Mondiale, DRM
broadcast transmissions on short wave ?
Again, here is the basic question
Have you ever heard on your radio a Digital Radio Mondiale , DRM broadcast transmission on short wave ?
And in case that your answer is yes:again, in case your answer is yes, give your impressions about those DRM broadcasts regarding quality and reliability of reception.
So, in case you have listened to DRM add your comments about quality and reliability of reception to your YES answer to the question.
As soon as all the answers are received here, I will once again, as I did about a year ago ,compile them and analyze them using standard statistical methods, and of course, made the results of this poll public, by reading them on the air, and publishing them on our website.
Your answers about DRM will certainly help to have a much better picture of what's happening with this technology amigos !
Now, let's go to Arnie's workshop, where an antenna project is in the works, to help several of the new local radio amateurs that have recently obtained their ham radio license.
This antenna is very easy to homebrew and has a very low cost. Readily available materials are used in the project and each antenna comes out of the workshop adjusted for minimum standing wave ratio .
This is a yet another variation of the so called SLIM JIM antenna, made using standard 300 ohms Television twin lead and a length of PVC pipe. The antennas here in Cuba are cut for 145.2 megaHertz , so that they will provide the lowest possible standing wave ratio between 144.5 and 145.5 megaHertz, the most used part of the two meters band all along the Cuban archipelago.
Cuban 2 meter band repeaters operate between 145.110 and 145.490 with one odd frequency repeater in Havana using the European R1 channel of 145.600 , and all use the minus 600 kiloHertz shift.
SLIM JIM antennas built using TV twin lead fitted inside PVC pipes are very rugged and reliable, and they are also very easy to transport and install, providing a lot of gain over the typical 2 meters band Handy talkie short vertical antennas that are connected directly to the rig, the so called rubber duck or more properly short helical loaded vertical antennas.
At my workshop, the standard procedure for assembling this antenna takes about one hour, and the antenna comes out with either a female coaxial connector at the bottom , or with a length of coaxial cable, usually about 3 meters or 10 feet to which a male coaxial connector is attached. The length of the PVC pipe is such that at the bottom of it there is room to fit a mast U clamp, so the antenna can be easily attached to any existing pipe mast.
Comparative measurements done between the Handy talkie's factory short antennas and our home brew one show that ours provides anywhere between 6 and up to 10 dB gain over the rubber duck antennas, depending on how long or how short the rubber duckies are, and to which part of the 2 meters band they are tuned.
Without any doubt this variation of the J pole antenna, also known as the SLIM JIM, shows better performance than the classic 300 ohm twin lead J pole, and that's why we are home brewing them here . Information provided at the website of Professor L.B.Cebik, that has the URL
www.cebik.com is extremely useful to help you to design a SLIM JIM antenna for the two meters band. again the URL or W4RNL website is www.cebik.com, where you will find lots of extremely useful and very well written as well as easy to understand antenna related information.
QSL on the air, QSL on the air, to all Dxers Unlimited's listeners that have requested the Hybrid Regenerodyne Homebrew Receiver files via e-mail... Now a the dot zip package is available for sending via e-mail but it took, yours truly quite some time because I must admit that I am not particularly good at doing computer electronic schematic diagrams... I do need to practice a lot more, so that the schematic diagrams come out faster.
The dot zip file contains all the required information to build the Hybrid Regenerodyne receiver and its power supply ,so I will start e-mailing it to all of you who have requested it. Let me remind you that this is a very flexible receiver design, aimed at experimenting on all bands from the AM medium wave broadcast band up to the 6 meters or 50 megaHertz amateur band.
The audio amplifier module and power supply are built on a separate chassis and are housed inside a nice wooden cabinet that serves also as the loudspeaker baffle, and this module will work very well also as a standalone unit for further radio hobby experiments that you may want to perform in the future.
The radio receiver's radio frequency module and detector are built on a separate chassis, with the regenerative vacuum tube detector contained into a very tightly shielded enclosure to prevent leak trough of signals at the detector's operating frequency from coming in. The detector's tuning range is practically unpopulated during the local daylight hours, but during the evening, signals in the range from 1.7 to 4.0 megaHertz may leak trough past the front end and into the detector, so that's the reason that the detector has to very extremely well shielded in an enclosure made of steel if possible, so that it will provide both magnetic and electrostatic shielding.
The regenerative detector's coil of the prototype was wound on a beautiful ceramic form, that I installed well removed from the walls of the enclosure, so as to keep the coil's Q as high as possible.
Si amigos, you may start thinking about the next radio project: Arnie Coro's Hybrid Homebrew Regenerodyne .... send your request to be included in the HHR receiver's mailing list to arnie@rhc.cu, again, arnie@rhc.cu, and all information about this and other regenerative receiver projects will be sent directly to your e-mail address amigos !!!
Radio is a wonderful hobby, and I can assure you that the unique experience of listening to a radio that you have built yourself is something that you have to experience in order to really understand it !!!
And now amigos, as always at the end of the show, here is Arnie Coro's HF plus low band VHF propagation update and forecast. Solar activity is way down, and we haven't seen more big solar flares during the past several weeks, .... Solar flux is now around 70 units and moving down, but, we may see periods of geomagnetic disturbances during the next two to three days. Local evening propagation conditions are going to be good between 3 and 15 megaHertz. At around local sunrise, the maximum usable frequency curve will show a very slow upward swing, because of the low solar flux prevailing at this moment. The Sporadic E season is now in full swing so watch for E skip signals on low band TV stations, channels 2 to 4 in the Americas, and for 10 and 6 meter amateur bands DX anywhere in the northern hemisphere. See you next Tuesday and Wednesday Sunday UTC days amigos, at the midweek edition of Dxers Unlimited. Don't forget to send your comments about this program to arnie@rhc.cu , or VIA AIR MAIL to Arnie Coro, Radio Havana Cuba, Havana, Cuba.
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