RADIO HABANA CUBA
DXERS UNLIMITED
MID-WEEK EDITION
TUESDAY, AUGUST 14, 2001
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hi, amigos RADIO-AFICIONADOS!!!! Welcome to the mid-week edition of your favorite radio hobby show, on shortwave and on the world wide web... I am Arnie Coro, radio amateur CO2KK your friend here in Havana, and here is our menu for today:
Item one: unexpected rise in the daily sunspot count, it happened on Monday... more about the solar cycle at the end of the show...
Item two: the low cost 11 or 13 components amateur radio single band transmitter that was described here during our weekend broadcast brought in a lot of feeback from listeners... Just a single type 7400 integrated circuit and an NPN power transistor plus a handful of easy to find electronic components delivers up to 7 watts, making possible some really nice CW contacts... more about the one IC plus one transistor rig, Arnie Coro's ONE PLUS ONE ham rig, later in the show...
Item three: YOU HAVE QUESTIONS, and Arnie tries to answer them... today I'll be answering a question sent in by about ten Dxers Unlimited's fans...
Item four: antenna topics section of the show, dealing today with the 0.28 wavelength vertical monopole and its many practical applications... by adding just.03 wavelength of wire or tubing to a quarter wave vertical, it becomes a much easier to match antenna and also a better perfoming one, too...
All this and maybe a litle more here at Dxers Unlimited's mid-week edition... My sound engineer and producer is Margarita Delgado... I am Arnie Coro in Havana, stay tuned.
Lots of e-mail messages from Dxers Unlimited's listeners around the world requesting more information about the low-cost, easy-to-assemble one IC plus one transistor low power amateur radio transmitter, my ONE PLUS ONE HAM RIG!!! And, YES, all the e-mail was answered during the weekend and Monday, so if you requested the circuit diagram of the one IC plus one transistor rig, take a look at your e-mailbox, as it should be there waiting for you already....
Among the questions asked, I think one was particularly important to answer over the air, and that was the one asking about what type of output power NPN RF transistors can be used in this rig. Well amigos, I have tested several of the most popular NPN RF transistors in the 5- to 10-watt power range with good results... The original one IC plus one transistor rig, the prototype, has a BD137 NPN audio transistor, a type of transistor with a high enough frequency cut-off to work easily up to the 20 meter amateur band... Remember that the output transistor must be selected both for its GAIN, and for the high frequency cut-off.
Normally you will want a transistor with enough gain and with a cut-off frequency of about 10 times the higher operating frequency... So, you can push a BD137 normally rated up to about 220 megaHertz to work up to the 20 meter or 14 megaHertz amateur band, and maybe higher too.
One of the problems with such simple rigs is that you must load them up into a well-matched antenna, otherwise you are running the risk of the high Standing Wave Ratio damaging the output transistor... The one IC plus one transistor rig uses no ferrite core or powdered iron toroids, something that makes things easier for the amateur who does not have access to such specialized high-tech components... I wound the rig's only coil using plastic insulated telephone wire on a length of one inch or 25 millimeters diameter PVC pipe. Others have used different coil forms, like 35 millimeter film cartridges or even the cardboard tube that is used for winding the toilet paper roll...
As you see, the little rig uses no rare and hard-to-find parts... as the variable capacitor is a standard radio receiver air insulated variable removed from an old AC-DC radio. I added to the first prototype's circuit a pair of additional disk ceramic decoupling capacitors of 0.1 microfarads each, and a carbon non-inductive 2-watt resistor. The capacitors are located right next to pin 14 of the IC to ground and right next to the coil's center tap to ground, providing additional bypass.
The 2-watt non-inductive resistor value has to be selected experimentally, it is connected between the output transistor emitter and ground, and its purpose is to provide protection to the output stage... You must experiment amigo! That's part of the fun... a carbon non-inductive resistor of about 15 ohms will be a good start-up point to begin testing your little rig... The power output with that high resistor value in the emitter circuit will be rather low, but using it you can find the right tuning spot for the variable capacitor, and check for possible auto-oscillations. Once you are sure the rig is working OK and delivering anywhere between 500 milliWatts and 2 Watts, you can start to reduce the value of the series emitter resistor.... In the prototype here, I ended up with a 2,2 ohm resistor....
AH!!! And before I forget, it is very important to use an appropriate heat sink for the output transistor... Use as large a heat sink as you can afford, and do follow the standard practice of using silicone compound between the transistor's body and the heat sink to enhance the transfer of heat....
As I said during our weekend show, the little one IC plus one transistor rig may be operated on 160, 80, 40,30and even on 20 meters, and you can run up to 15 or even 18 volts to the output transistor's collector, again with a good-sized heat sink. The slight inconvenience of requiring two different operating voltages, 5 volts regulated for the IC and between 10 and 18 volts DC for the output transistor stage, is more than offset by the very easy to build and adjust circuit!!! As a matter of fact, the little one plus one rig is ALSO an excellent code practice oscillator, quartz crystal tester and frequency marker, besides providing enough Radio Frequency output power to allow your amateur radio station to contact stations half way around the world when propagation conditions are in good shape!
Again, the circuit diagram and a brief text description of the ONE PLUS ONE, the one integrated circuit plus one transistor amateur radio transmitter is available to you by just sending an e-mail message to arnie@radiohc.org, or if not yet in cyberspace, send an AIRMAIL post card to Arnie Coro Radio Havana Cuba, Havana, Cuba and ask for the ONE PLUS ONE INFO PACKAGE, and Irma Veitia from our correspondence department will send the textfile and the circuit diagram to you. Let's hope that in the not-too-distant future we will have the nice opportunity of making a nice two-way CW QSO with Dxers Unlimited's listeners that have built this little rig. The ONE PLUS ONE, one of the best practical examples that amateur radio need not be an expensive hobby amigos!!!!
You are listening to the mid-week edition of Dxers Unlimited amigos, and now here is our popular "you have questions and Arnie tries to answer them." Today's question was sent in by 10 listeners of the show... They all want to know what is going to happen as soon as international short wave broadcast stations start using the new DIGITAL RADIO MONDIALE system...
Well amigos, here is my very short answer: Don't worry about DRM, it is still in its infancy, and so far there are no commercially made professional receivers for decoding DRM signals, and as expected consumer radios for the new DRM signals are non-existent at this moment. So doing some crystal ball analysis here, we will surely see a long transition period during which both standard analog AM broadcasts and DRM digital broadcasts will be made available to short wave listeners simultaneously. IF the new DRM technology proves to be really effective and the radios can be mass-produced at low cost, then analog AM short wave broadcasts will slowly fade out of the picture, in a way similar to what has happened to Morse code CW radiotelegraphy after satellite systems became available for search and rescue emergency operations.
NOW just a short note that answers another listener's question: SI, AMIGO, YES MY FRIEND, if you are going to install a vertical antenna, it is ALWAYS a very good idea to make the vertical element longer than a quarter wavelength. By just moving up to 0.28 wavelength, your base impedance will go up very near 50 ohms, making the matching to 50 ohm coaxial cable a lot easier... and if you want your signals to travel much farther, extending the length of the vertical element to around 120 electrical degrees is a very good idea indeed... BUT, matching the 120 electrical degrees long vertical is a bit more complicated.... Anyway, in an upcoming edition of Dxers Unlimited, I'll tell you more about vertical antennas that are both easy to build and do perform nicely.
And now as always at the end of the show, here is Arnie Coro's Dxers Unlimited HF plus 6 meters propagation update and forecast:
Solar flux was near 150 Tuesday morning, the number of sunspots went down to 141, after a unusal increase that happened on Monday... The effective sunspot number, that's the figure to feed your propagation forecating software was 107, and the A index, the planetary geomagnetic disturbance indicator was still rather high, near 15, but moving down as the effects of the gust of solar wind are now almost over.
Expect nice DX conditions after sunset on the 15 and 13 meter bands, lasting for several hours, and we have received reports of several late season sporadic E openings... Now we are only 3 weeks away from the beginning of the wonderful autumn equinoctial DX season, when we all should be able to enjoy some excellent propagation conditions even at the top end of the HF spectrum, so have those 10 and 12 meter band antennas ready for action, amigos!
Arnie Coro CO2KK
Havana, Cuba
August 14, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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