By Arnie Coro
radio amateur CO2KK
Hola amigos radioaficionados all around the world, now listening to the weekend edition of Dxers Unlimited. I am your host Arnaldo, Arnie, Coro, radio amateur CO2KK wishing you excellent reception of this program. yes this is for sure the one and only radio hobby program covering all aspects of our wonderful way of really having a good time playing with our radios….
Item one : Solar activity update…. Provisional International monthly mean Sunspot Number for November 2018 : 5.9 (five point nine) , again 5.9 ie the provisional international monthly mean Sunspot number for the month of November…. Now more data:
Maximum : 15 on 12, 16, 17, 24
Minimum : 0 on 1, 2, 3, 4, 5, 6, 7, 11, 20, 21, 22, 23, 27, 28, 29, 30
Predictions of the monthly smoothed Sunspot Number using the last provisional value, calculated for May 2018 : 7.5 (+-5%) This very accurate data about solar activity confirms that cycle 24 is still in progress, moving slowly towards its minimum and I may add that several small reverse polarity high latitude sunspots reported recently confirm that solar cycle 25 is now beginning…..
Last week I asked the question …. Have you ever tried assembling a crystal radio set ? Adding my comments that crystal radios provide the builder with a unique experience by picking up radio stations with a receiver radio that uses no batteries or connection to power lines. Today I want to tell you more about one of the best performance crystal sets ever designed, the brainchild of the famous American radio wizard Ben Tongue of Blonder Tongue Laboratories fame.
Yes amigos , there are more than 91 well documented different ways of enjoying the radio hobby, and here I am to tell you about some of them today. From La Habana Cuba this is the the weekend edition of Dxers Unlimited, and here is item one…
Requests about the circuit diagrams and building instructions several of Ben Tongue’s super efficient crystal radio sets continue to reach me, and as usual I have already sent them via e mail to those who asked for that valuable and unique information….. Also requests for my Super Islander Mark Six direct conversion short wave receiver keep coming in to my email inforhc at enet dot cu…. and as soon as they are received, it takes just a few seconds to send the electronic reply via the Internet…
By the way listeners that have built the different versions of this receiver, that forms part as a module of a more complex amateur bands transceiver tell me that the project was an easy going task that could be built using standard available parts. By the way, my Super Islander Mark Six direct conversion receiver is sensitive enough that it can also form part of a minimalist low cost amateur radio station that uses separate receiver and transmitter modules with a common power supply.
Yes amigos I am really happy about how listeners keep telling me how pleased they are about its performance, and also comment about the fact that the Super Islander Mark Six receiver uses no rare , hard to find electronic components.
More feedback from listeners of this program…. Another Dxers Unlimited fan told me via e’mail that he was amazed by the excellent performance of the very simple single transistor product detector mixer circuit, used in that direct conversion type of receiver , that was easy to set up and provides an extra conversion gain when compared with diode detectors. So far all builders of the Super Islander Mark Six direct conversion receiver have opted for a frequency coverage within the range between about 4 and 10 megaHertz , with special emphasis on a bandspread option that covers the first two hundred hiloHertz of the 40 meters amateur band where most local and DX activity is concentrated.
This is Radio Havana Cuba, the name of the program is Dxers Unlimited and it is on the air twice every week, promoting the enjoyment of this wonderful hobby… Now item three:
More about the Super Islander Mark Six receiver schematic…. Using battery power supply is essential for optimum performance of direct conversion receivers in general and my Super Islander Mark Six is no exception. I also recommend the use of a variable tuning dual bandpass input filter between the antenna and the radio frequency amplifier stage because it helps to suppress out of band signals. As a matter of fact inserting well designed bandpass input filters ahead of any radio receiver that covers the short wave spectrum has improved the performance of many low cost radios..
By the way, yes I confirm that my dual tuned bandpass input filter has its coils wound on small plastic medicine bottles, that are fixed to the printed circuit board by glueing the cap with epoxy cement or super glue to the board , and then you just carefully screw the pills container coil form to the captive cap….
I have built the standard two sections RF filter and a three sections version using a very simple screening enclosure made from pieces of double sided circuit boards… If you are good at cutting those circuit boards nice and square, the input filter module will have very nice looks, something everyone that sees the prototype likes to comment…
Following the dual tuned bandpass input filter is the cascode variable gain radio frequency amplifier stage, made with two quite common NPN silicon transistors, type 2N2222 or similar ones… The circuit is very stable and it feeds the one transistor product detector that uses also a 2N2222 or a higher gain low noise transistor if you want to squeeze more gain and reduce the conversion noise.
After the product detector comes the audio module sub assembly, that already exists in two versions, one a very simple low parts count one, and the other more complex board that includes two audio filters that are in my opinion a really worthwhile addition to this and many other home brew radio receiver projects.
Poor propagation conditions during last week’s program brought reports from listeners asking to repeat the ASK ARNIE section of the show. Now let me reply again to the question sent by listener Rex from London, Ontario, Canada… Rex asked how he could listen to the 49 meters band, that is the 6 megaHertz region of the short wave spectrum using the regular Super Islander Mark Six he has just built …. and here is the answer. You simply retune the VFO, down from the 7 megaHertz minimum frequency for the 40 meters band coverage by adding a few more turns to the tuning coil of the variable frequency oscillator to achieve a coverage from about five point nine to six point two megaHertz…..
Amigo Rex! if you want to pick up our 6000 kiloHertz or our six thousand one hundred and sixty five kiloHertz English language evening broadcasts using the Super Islander Mark Six, then you must use a reception mode known as EXALTED CARRIER RECEPTION…
It is really very easy to use it in practice, just zero beat the carrier of the AM station… and the audio will come out nice and clear… if your VFO is stable, it is going to stay in full synchronization with the station’s carrier frequency … Exalted carrier reception has its advantages too, and any single side band receiver can be used for picking up AM broadcast stations using it with a great advantage…
Yes amigos, si my friends, oui mes amis… a low parts count, straightforward radio receiver design that you can home brew and use it later as a platform for making many experiments, including a band switching arrangement with up to date frequency synthesizers is available by the name Arnie Coro’s Super Islander Mark Six. You can send for the circuit diagram and a text file with the how to build it instructions by just sending an e’mail to inforhc at enet dot cu… again , inforhc at enet dot cu, or Via Air Mail to Arnie Coro, Radio Havana Cuba, Havana, Cuba
Now our next radio hobby related item, the topic, aircraft scatter signals reflections, now in use by some experimentally minded radio amateurs who happen to live nearby to highly traveled airways…. If you have operated a 2 meters or a 70 centimeters FM amateur transceiver, the aircraft scatter propagation mode may have shown up in the form of sudden signals enhancements and a special form of flutter… when a large sized aircraft is along the propagation path between you and another station… Aircraft scatter signals can extend the range of the regular two or 70 centimeters band stations by at least two hundred miles or even more, and you will not require any special equipment or training to use this unique form of propagation.
See you all at the middle of the week edition on the air Tuesday and Wednesday UTC amigos, just after the half hour news bulletin here at Radio Havana Cuba