Revision 3. Indirect Statement 2. Indirect Command and Request 3. Indirect Questions 3. Reporting a Dialogue or a Conversation 5. Conditional Sentences 1. Making a Wish 3. Formation of Nouns 2. Classification of Nouns 3. The Category of Number 4. The Category of Case 5. Use of Articles with Common Nouns 1. Use of Articles with Proper Nouns 3. Special Difficulties in the Use of Articles 4. Use of Articles in Some Set Expressions 6. Classification of Pronouns 1.
Formation of Adjectives 2. Word Order: Adjective Noun 3. The Comparison of Adjectives 4. Definition, Forms and Place 2. Classification of Adverbs 2. The Gerund 1. The Infinitive 2.
The Participle 3. Definition 2. Prepositions of Place 2. Prepositions of Direction 4. Some Prepositions Confused 5. Revision 6. Prepositions with Forms of Transport 7. The Prepositions of Time 7. Prepositions Expressing Abstract Relations 8. Composite Prepositions Revision Use of Prepositions in Set Expressions The Compound Sentence 2.
The Complex Sentence 2. Subject Clauses 2. Predicative Clauses 2. Object Clauses 2. Attributive Clauses 2. Adverbial Clauses 2. The Emphatic 'Do' 2. Double Negation 3. The Emphatic Construction 'It is. The Emphatic Construction 'It is not until. The Emphatic 'Not. List of Grammar Terms and Keywords Appendix 2.
List of Irregular Verbs Appendix3. Regular Verbs: Spelling Rules Appendix 5. Place and Order of Adverbs in a Sentence Appendix 6. American English Appendix 7. Punctuation Appendix 8. Prepositions and Homonymous Adverbs. Meaning and Use Literature Read more.
Show less. Jism 2. The five magazi nes I sold to IDG. So I can understand what happened at Polaroid. Today I need to buy a good digital cum- em. Am I consideri ng a Kodak'! Har-dc- har. Should I get the latest Nikon. Well , my fil m cam- eras are Olympus and Nikon - mostl y Nikon - so I' ll probably senlc for a Nikon Cool pix digital camera.
Cooked Goose Don't you pi ty the poor bastards who arc addicted to cocaine or heroi n? And those kids exhibiting the monumental stupidity of smoking, bui lding one hell of a lifetime though shall addict ion? Yo u' re a drug addict. No, I'm not talking about drugs like caffeine or alcohol, I' m talking about eating cooked or processed food. I' ve written about all of them except Dr. Edward Ho well. I even review their books in my Wisdom Guide.
Howell ' s research sho wed that rats fed coo ked and processed food li ved about two years. Those eating raw food li ved about three years. In people years that' s the diffe rence between living 75 years our c urrent average and 11 2. Rats fed only processed food ga l fatter and fancr, while their brain weight went down. Howell reported thai before Eskimos were introduced to a cooked diet they mainly lived on raw whale and seal blubber and meat - with no heart dis- ease, cancers, high blood pressure.
They li ved long, healt hy li ves. A stud y was done wit h hogs, where o ne group was fed cooked spuds and the other raw potatoes. Those eating the cooked po tatoes gained we ight rapidly.
Those fed raw potatoes didn't get tar, Howell Slates, "It is impo.. Icing Up Si nce o ur media seems totally fi xat ed on global warming. And that' s the hard packed st uff. Zillions of tons of it. Some global meltdown. In a past essay I included a photo of a hundred-foot derrick in Antarctica which was almost covered in snow after j ust a few years.
So what? One has to do wi th Antarctica not being centered over the Sout h Pol e. If you' ll check the map supple ment in the February National Geographic. I' ve gone into some det ail on the pre- dictions by Nostradamus. Edgar Cayce, and other noted prophets on the co ming virtual ext inction of humanity.
Co ming soon. Prophcts-sbrnofet s. Then you sure haven't been paying attention to my editorial essays where I' ve reviewed the books showing that precognition has been scientifically proven 10 he real. Read Dean Radin' s 71,e Conscious Uni verse. Read my booklet o n [JOin ing. Another thing not good?
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Switched mode power supplies SMPS are relative newcomers to the electronics world. In days gone by, motor-generators, dynamotors, or vibrator supplies were used to convert a battery voltage to some other voltage. Today SMPSes do that job. They are small, lightweight, and relatively inexpensive, and within the construction capability of the home brewer.
The 60 Hz transformers and chokes arc big and heavy, hut they arc devi ls we know and have learned to li ve with. But when we need to operate from a bat- tery. Of course, we can still generate 60 Hz with a motor generator T he power density, watts-per-cu. While some newer SMPSes have den- sities of 20 watts-per-cubic- inch, most home bui lders will accept a much lower power density. The home-built supplies may not be the most compact.
Instead of generating 60 Hz, why not 60 kH:t. The trans- formers and induct ors wi ll be much smaller and the filtering much easier. Arguing against a hi gh frequency is component availabilit y. High frequency transformers arc small and easy to wind: A few turns on a ferrite core for an SMPS looks pretty good. As an example, obtaining 28 volts from a 12 volt source can he achieved with a DCIDC converter: A high fre- quency osci llaLor followed by an am- plifier.
Then rectified and filtered. Thi s solution is certai nly simple, hut it has no regulation and must be manually adjusted. SNIPSes arc regulated and often have a lot of other hells and whist les not essential to generati ng a stable voltage such as over or under voltage protecti on, current limiting.
Once you know what the necessary parts are and what they do you can add these extra funct ions. Ssqs filIId progr1tll nlllblt.. What were tri vial parasitics at 60 Hz become serious problems at 60 kHz and at kHz everything is critical : Leads " Ii " j.. ReputerCW lD. Operating with higher frequencies voltage changes or as the load changes. An unregulated supply is certainly simple, but adding regulation need not be a deal breaker.
It can be as simple as following the unregulated supply with a zenor diode or a three terminal regu- Iator, This is a rather inefficient ap- proach. Another more complex but efficient method is to control the drive to the power oscillat or. An even more complex scheme is to sense the DC output and automatically control the. This is an SMPS. Controlling the output power of an SMPS isn' t like controlling the output of a linear amplifier. The output power is controlled by changi ng the duty cycle of the drive.
A push-pull ampli- fier is shown in Fi g. When each transi stor is on for full alternate hal f r - - - - - - - - - - - - - - - - - - - - cycles the output will be maximum, but when each transi stor is on for only a part of the half cycle, the output will be less. Changing the duty cycl e of the drive is the smart way to change the output voltage. RI j ust stabilizes the frequency with changes in supply voltage.
RI can have any value but something in the range of three to ten times R2 is typi cal. Large values of RI can limit the maximum frequency, so at kHz a value of about three limes R2 is safe.
The output of the monostable, U2A and U28, is approximately 11O. When R5 is made variable the pul se width can be varied. R5 controls the DC output of the converter. A pulsewidth: modulator is an essential part ofan SMPS. A sample of the DC output can be f ed back to control the output. The di ode' s di ssipation is in- creased and the load on the source is al so much hi gher than expected.
The rippl e increases as well. All in all a bad si tuation. Schottky diodes and ultra fast diodes have much shorter reverse recovery times and minimize reverse recovery prohlems. Schott ky diodes arc an ex- cellent choice in that they have reverse recovery times of a few picoseconds and forward voltage drops of about 0. Unfortunately Schottky di- odes have a PlY peak inverse voltage of only about 30 or 40 volts.
Us ing ultra fast diodes like the Motorola MUR or 41 0 provide a nice safety factor for operating frequencies of several hundred kilohertz. The power amplifier and rectifiers are shown in Fig. While MOSFETs are voltage con- trolled de vices, it takes time to charge their input capacitance and raise the gate voltage.
The capacity at the input is not just the gate-source capacity plus the gate to drain capacity; the old bug-a-boo Mill er effect gets into the act. The input capacity of an amplifier with a resi sti ve load is: is the gate-source capacity, is the gate-drain capac ity, and A is the voltage gain. To complicate the maucr, C gd is not constant like in a vacuum tube but changes with gate to drain voltage. MOSFET manufacturers gi ve the in- put capacity in terms of the total charge needed to be charged to switch the rated drain current when the supply is the rated drain voltage.
Since MOSFETs are maj- ority carrier de- vices, they do not suffer from re- covery time, and when dri ven hard enough can switch in a few nanosec- onds.
Diode reverse recovery time is a different problem. During the reverse recovery time a di- ode conducts equal- ly well in the re- verse direction, not a good situation. Reverse recovery times of diodes is short enough to he ignored at 60 HI" but at higher fre- quencies reverse recovery time can be a signifi cant frac- tion of the period of the operating fre- quency.
Ignore reverse recovery time at your peril. Ordinary silicon rectifi ers begin to depart from the ideal at a kilohertz or so. For example, the INX series of silicon rectifiers has recovery times of about nsec. That is, the di ode continues to con- duct in the reverse direction for 0. When the frequency is 20 kHz the polarity changes every 25 usee and 0. Reverse recovery time of di odes, and storage time of bipolar transi stors add to the design problems. Operates on VOC. Great for attention gelling displays, party oecoratlons, nighf time warning signal s A red 5mm LED with flasher chip is attached to a battery snap that snaps onto a 2 AA cell batlery holder.
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Quan"""" Lon"ad. N 2 , the turns ratio squared, 1. The magnetizing impedance should be greater than 5. A toroidal transformer wound on a core of Ferronics B material is quite suitable for frequencies up to kHz. As a first cut the 11 core is large enough to comfortably accommodate the necessary windings, but as wi ll be shown a single core will saturate. Two cores stacked can increase the effective area and ease that concern.
L computes to be 12 IJ. H for one turn. A usable flux density is less than 3, Gauss in each core. For two stacked cores the flux density is 7, Gauss.
A L is the inductance index, the ductance of one turn. A l is given as 6, nH for the 11 - core. When two cores are stacked, A e doubles and doubles the inductive index. Remember, each pass of the wire through the hole is one turn. The transformer has 2 turns cen- tertapped for the primary and 8 turns ccntertapped for the secondary, or a turns ratio of four to one.
The second- ary impedance reflected into each half of the primary is IIN 2 or 1. The magnetizing impedance of each half of the pri mary is 21tfL p or 7. The total current in the primary is the magnetizing current plus the reflected secondary current. The maximum The gate current is a spike of current that decays exponentially to zero as the input capacitance is charged.
But the peak current is still rnA. The output current of the CMOS gates is only a couple of mils so that more cur- rent is requi red to switch quickly. Emitter followers QI and Q2 provide the higher current. Since the emitter followers are not saturated their ri se and fall times are fast.
The transformer is a crucial item in the design of the supply. Designing the proper transformer is not a walk in the park, but it' s not a deal breaker.
Selection of the wire size depends on the currents involved, and the num- ber of turns depends on the required inductance and the step-up desi red. The ampere turns dictate the core size. The turns ratio sets the step up or down of the voltage. If the main DC source i s a 12 V car battery, the voltage can vary from 9 V to If it is desired to build a 28 V 1 A supply powered from a car battery, a ratio transformer would step up 9 volts to about 36 volts peak and step up With reasonable transformer efficiency and losses in the amplifier and rectifi- ers, the output should he 30 V mini- mum and at least 50 V maximum.
A toroid will probably be easier to work with than a pot core, but compromises will have to be made. The turns ratios must be whole numbers. Selecting a core that has the perme- abi lity and saturation characteristics is the key consi deration. The impedance of the primary with the secondary open should be as large as practical, certainly greater than three times the loaded impedance. The secondary im- pedance reflected into the primary is the secondary impedance di vided by 73 Amateur Radio Today.
March 13 Fig. The TL J is a switch mode pulsewidth modulation controt l C. U2 is a com- parator that controls the amplitude of the sawtooth. U3 compares the saw- tooth voltage with a pul ses.. The sawtooth ampli tude is deter- mined hy the hysteresis around U2. Whe n the vo ltage on CI the output of UI exceeds the voltage on the nonin- vert ing input of the comparator U2, the output of U2 goes to near zero and Cl is discharged through DI toward 0.
When the volt- age on CI fa lls below the voltage on the inverti ng input. Wi th a 10 volt supply and the values shown in Fig.
The positi ve going output ofU2 also provi des the clock for U4 of Fig. The frequency of the sawtooth is de- tcnnined by how rapidly the voltage on CI rises from 0. A charging current of 0. The constant current charging CI is obtained wi th QI.
R I controls the gate source vol tage, and consequently the drain current. For the 2N Under these condi tions R I would be 1. Unfortunately, the drain current vs. A variable R l of 5k will probably suffice. While the value of R I can be calculated, a more pract ical solution is to just adj ust the source resistor to produce 0. If yo u want to do the math, an accu- rate prediction of the val ue of RI can be made when the parameters of the per amp.
In a mul ti-layer wi nding transformer the wi re size should be greater than circular mils per amp. As an aside, MIL specs limit the wi re size in a harness to at least circular mils per amp. The core has enough ID to easil y allow 18 AWG to be used for both the primary and sec- ondary. The temperature rise of 18 should be well within the temperature limits of any enameled wi re.
Pcrmvar may be a bi t diffi- cult to strip. A pulse width modulator PWM shown in Fig. The PWM is a basi c functional block of all switched mode power supplies. The vari able pulsewidth in the our- put of U3 of Fig. Decreasing the vol t- age narrows the output pulse. The sawtooth is generated by a con- stant current linearly chargi ng the ca- pacitor Cl.
The voltage on C I is isolated from the following circuits by magn enzmg current exists when the main battery voltage is maximum. The maximum total n ux B is J. The transformer can be wound on ei- ther a ferrite potcorc or a toroid core. In most cases a toroi d is easier to come by and gaping the core is avoided. In either case, a good rule of thumb is to make the primary 's magnetizing cur- rent.
That is make the inductance as high as practical. A two turn primary would have an induc- tance of 48 ohms but the field strength would be 2. Selecting a core is primarily a matter of finding a core that can support the needed ampere-turns without saturat- ing the core. That is, keeping the mag- netic flux Gauss be low the saturation point of the core. The core material de- termines the field strength Oersteds that can be supported.
The wire size used depends on the RMS curre nt the wire will be carryi ng. The val- ues given in the data sheets for the 2N arc pretty loose: l oss' the drain current with gate-source volt- age zero, is between 5 rnA and 1 rnA, and cutoff voltage Voff' the gate- source voltage that reduces the drain current to less than I uA, is between 0.
The MPFI02 limits are looser. Not very close, but all is not lost. A supply of 6 to 20 volts or so, a resi s- tor in the order of 10k and a voltmeter and milliammeter will be needed. Con- nect the positive voltage to the drain and the negative side to the source.
Short the gate to source of the JFET and measure the drain current loss. Connect a 10k or so resistor in the source. Measure the voltage V g , across the resistor and the resulting drain cur- rent I o ' With Vp and I D known, the value of V,, f can he computed with equation 3. With these values of l oss and V olf established, the gate-source voltage needed to produce a parti cular drain current can be calculated with equation I.
The drain current of a JFET is essen- tially independent of the drain-source voltage when the drain-source voltage is above pinch-off. For a typical 2N, pinch-off is a couple of volts for drain current of less than I rnA.
In Fig. PWM is accomplished by comparing the sawtooth voltage to a variable control voltage obtained from potentiometer R6. When the sawtooth voltage on the inverting input of U3 is less positive than the voltage on the noninverting input, the output is high and stays high until the sawtooth ex- ceeds the voltage on the inverting in- put. Reducing the positi ve voltage to the inverting input from R6 decreases the width of the positive pul se on the output of U3, and increases the width of the low.
In a D flip- flop. The outputs arc kHz square waves kHz divided by 2 Continued on page 16 3 days. Unsurpassed Outside Vending: Area. Ut enimnisi ut aliquipea. Our innovative 5-step web development process helps us to develop a variety of websites. Ranging in complexity from small static sites to large enterprise solutions, the process below helps us deliver perfection every time.
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In this talk, Colin will discuss some of the common space weather indices, their sources and possible meanings and how a deeper understanding of these may be used to understand HF propagation through the ionosphere. He will talk about his experiences and experiments in Uganda and Rwanda. Useful for travellers but also for UK operators trying to put out a good signal with a quite simple antenna. Contest Hints from Start to Finish by Lee Volante, G0MTN A selection of tips and ideas suitable for newcomers to contesting, but which will also give the more experienced contest entrant something to think about.
Areas covered include pre-contest planning and analysis, station design, and of course on-air operating skills development. Come and see how TV home makeover shows are relevant to contesting! It will be a general talk with no detailed setting up of the station.
I shall discuss what software to use, where to find RTTY and PSK, some hints and tips on setting up the equipment and macros in order to enhance their operating on datamodes. Make the Most of Your Antenna Opportunities by Steve Knowles, G3UFY A fairly light-hearted, very-low-mathematics look at antennas for those just coming into contesting, especially those with limited space and resources, including the briefest of introductions to modelling and Polar Diagrams.
Should you compromise or specialise—or convenience vs inconvenience? By looking at some popular designs Steve will try and answer that question as well as deal with. Store-bought or homebrew and care and maintenance dealing with safety issues where prevention is better than cure.
Sporadic-E by Jim Bacon, G3YLA Jim will be bringing us up to date on the latest season of Sporadic-E and revealing the results of some new techniques to try to second guess the likely locations. He will also introduce a new item to the amateur radio community from the world of weather and propagation with a review of current research to examine the effects of climate change upon the ionosphere.
Knowledge of the duct parameters—e.
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