RADIO HABANA CUBA
DXERS UNLIMITED
WEEKEND EDITION
SATURDAY, SEPTEMBER 1, 2001
By Arnie Coro CO2KKSend your comments, questions and ideas to: arnie@radiohc.org
Hi, amigos RADIO-AFICIONADOS!!!! Welcome to the weekend 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: once again solar cycle 23 is producing some very interesting activity... 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 I described here during a recent broadcast continues to bring in a lot of feeback from listeners...
At the San Cristobal Radio Club in Pinar del Rio, western Cuba, Jose Luis CM2LM stroke one tested the circuit and sent an e-mail telling me that he was amazed how the 7400 would make very sluggish quartz crystals oscillate, even some that won't oscillate at all using other traditional circuits, 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...Our long-time friend Bruce VE6XTC wants to know why resistors used in electronics have such odd values, instead of what he thinks are more logical round number values... stay here, and you will learn why resistors are made in one percent, five percent, ten percent and twenty percent tolerance series...
Item four: antenna topics section of the show dealing today with the 0.33 wavelength vertical monopole and its many practical applications ...and you will learn about one of Arnie Coro's tricks to use 75 ohms coaxial cable, yes the one that is plentiful and costs less, with these 0.33 wavelength long vertical antennas, YES, by making it just 0.33 wavelength of wire or tubing it becomes a much easier to match antenna, and also a better perfoming one too, as your take off angle will be LOWER!!!
All this and maybe a litle more here at Dxers Unlimited's weekend 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, and as always, those who have sent their request via e-mail have enjoyed our super fast answer... See, I read all the e-mail sent to arnie@radiohc.org several times each day, so usually the answers to your questions and request for our popular TECHNICAL INFO PACKAGES goes via INTERNET the same day I receive it....So at the request of many listeners, here is a review of the ONE PLUS ONE QRP or low power very simple amateur radio transmitter.
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...As this question keeps coming in from many listeners, here is the answer once again:
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 cutoff to work easily up to the 20 meter amateur band...There are many NPN medium power audio transistors that have a transition frequency, an Ft high enough to make them good candidates for the output stage of the ONE PLUS ONE, but, if you have the opportunity of using an NPN transistor specifically designed for Class C or D RF service, by all means use it!!!
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 a 220 megaHertz transition frequency to work up to the 20 meter or 14 megaHertz amateur band, and maybe higher too. By the way, the transition frequency of a solid state device is the frequency at which amplification becomes unity, in other words, the frequency at which the transistor in this case ceases to amplify at all!!!
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, and this applies to ALL SOLID STATE OUTPUT STAGE RIGS...
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... later I assembled a second rig, and this time I wound the coil using a one and one half inch or 37 millimeters diameter PVC pipe, and that coil required, as expected, a smaller number of turns.
In the most recently built ONE PLUS ONE rig, which is now almost ready, I used an epoxy fiberglass board that includes the 4.7 volts zener diode and dropping resistor needed to power the 7400 integrated circuit from the PLUS 12 volts supply...
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, something very useful when you are experimenting and SURE -- you must experiment, amigo! That's part of the fun...
A carbon non-inductive resistor of about 15 ohms will be a good startup 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 have explained here previously, this little one IC plus one transistor rig may be operated on 160, 80, 40,30 and 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!!!
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 text file and the circuit diagram to you...
You are listening to the weekend edition of Dxers Unlimited, amigos... and here now is our popular "you have questions and Arnie tries to answer them!" Today's question sent in by Bruce VE6XTC. He wants to know why resistors used in electronics have such odd values:
Arnie, why is a resistor marked 470 ohms or 560 ohms instead of 500 or 550 ohms?Well amigo Bruce, electronic designers and manufacturers -- in the era before integrated circuits made their appearance -- decided to use three or four standard value series resistors of specific tolerance. That is, one percent tolerance, five percent tolerance, and usually twenty percent tolerance. The idea behind this decision is a very clever one, as the standard series of component values would make possible very easy to follow electronic designs...
See amigo Bruce, let's say you have a resistor of 470 ohms, a twenty percent component may come out of the factory with an actual real value of very near 550 ohms if on the high side, and very near 420 ohms if on the low side.... Following this logic, you will then realize that the series of values are dependent on the tolerance of the components... twenty percent components are the most common and less expensive ones, ten percent components are more expensive, but you can select closer values for your applications, while 5 percent tolerance components were only considered at some very specific circuit applications because of the fact that they are more expensive. One percent tolerance parts are still more expensive, and thus used only in critical circuit applications... The same idea applies to capacitors, again explaining the rather odd values like 68 picofarads, 91 picofarads and the like!!!
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 0.33 wavelength, that is a vertical element that is one third of a wavelength long, your base impedance will go up very near 75 ohms, making the matching to standard low cost 75 ohm TV type coaxial cable a lot easier... All you will need between the center conductor of the coaxial cable and the base of the vertical is a series capacitor to cancel the reactance present there... Here I use the 0.33 wavelength vertical for the 2 meter ham band... It is a very inexpensive and effective antenna when you use it with 4 radials in a ground plane configuration...
The 0.33 wavelength vertical is my favorite low cost antenna for Dxing on 10 meters with my little 25 watt SSB and CW rig, the one I keep right next to the computer.... So whenever I am writing a script or running new software, the 10 meter band radio, connected to the one third wavelength long vertical is kept scanning from 28.1 to 28.5 megaHertz searching for possible openings.... that's why I catch so many 10 meter band openings, amigos... the beacons that operate from 28.2 to 28.3 megaHertz will tell me that the band is open, even when there is no amateur station on the air and then, after picking up the beacon or beacons that are a surefire indication that there is propagation, I start calling CQ DX... and in most instances one or several amateurs come back to my calls. SI AMIGOS... YES MY FRIENDS... OUI MES AMIS, the TEN METER HAM BAND is open for DX much more than anyone can imagine... Monitor the 10 meter BAND BEACONS from 28.2 to 28.3 megaHertz and you will hear it for yourself...
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 activity during the past few days has been mostly MODERATE and several Solar Flares have erupted, sending first radiation towards the Earth and later, charged particles that have disturbed the planet's magnetosphere... There are now three solar active regions that could at anytime generate more flares... SOLAR FLUX is very near 200 units, and that is a very good figure, as the combination of an approaching equinoctial season and solar flux above 150 units is ideal for the higher frequency bands to open up during the local daylight hours and just after sunset...
Now we are only one week 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!
Prepared 01-Sep-2001; received by NY Transfer 03-Sep-2001
Arnie Coro CO2KK
Havana, Cuba
September 1, 2001Postal address:
Arnie Coro, "Dxers Unlimited"
Radio Havana Cuba, Havana, CUBA
e-mail: arnie@radiohc.org
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