|Главная Журналы Популярное Audi - почему их так назвали? Как появилась марка Bmw? Откуда появился Lexus? Достижения и устремления Mercedes-Benz Первые модели Chevrolet Электромобиль Nissan Leaf||
Главная » Журналы » Simple coaxial reflectometer
1 2 3 4 ... 80
simple coaxial reflectometer
The field of radio is a division of die much larger field of electronics. Radio itself is such a broad study that it is still further broken down into a number of smaller fields of which only shortwave or high-frequency radio is covered in this book. Specifically the field of communication on frequencies from 1.8 to 450 megacycles is taken as the subject matter for this work.
The largest group of persons interested in the subject of high-frequency communication is the more than 150,000 radio amateurs located in nearly all countries of the world. Strictly speaking, a radio amateur is anyone interested in radio non-commercially, but the term is ordinarily applied only to those hobbyists possessing transmitting equipment and a license from the government.
It was for the radio amateur, and particularly for the serious and more advanced amateur, that most of the equipment described in this book was developed. However, in each equipment group simple items also are shown for the student or beginner. The design principles behind the equipment for high-frequency radio communication are of course the same whether the equipment is to be used for commercial, military, or amateur purposes, the principal differences lying in construction practices, and in the tolerances and safety factors placed upon components.
With the increasing complexity of high-fte-quency communication, resulting primarily from increased utilization of the available spectrum, it becomes necessary to delve more deeply into the basic principles underlying radio communication, both from the standpoint of equipment design and operation and from the standpoint of signal propagation. Hence, it will be found that this edition of the RADIO HANDBOOK has been devoted in greater proportion
to the teaching of the principles of equipment design and signalpropagation.lt is in response to requests from schools and agencies of the Department of Defense, in addition to persistent requests from the amateur radio fraternity, that coverage of these principles has been expanded.
Amateur radio is a fascinating hobby with many phases. So strong is the fascination offered by this hobby that many executives, engineers, and military and commercial operators enjoy amateur radio as an avocation even though they are also engaged in the radio field commercially. It captures and holds the interest of many people in all walks of life, and in all countries of the world where amateur activities are permitted by law.
Amateurs have rendered much public service through furnishing communications to and from die outside world in cases where disaster has isolated an area by severing all wire communications. Amateurs have a proud record of heroism and service in such occasion. Many expeditions to remote places have been kept in touch with home by communication with amateur stations on the high frequencies. The amateurs fine record of performance with the wireless equipment of World War 1 has been surpassed by his outstanding service in World War II.
By the time peace came in the Pacific in the summer of 1945, many thousand amateur operators were serving in the allied armed forces. They had supplied the army, navy, marines, coast guard, merchant marine, civil service, war plants, and civilian defense organizations with trained personnel for radio,
radar, wire, and visual communications and for teaching. Even now, at the time of this writing, amateurs are being called back into the expanded defense forces, are returning to defense plants where their skills are critically needed, and are being organized into communication units as an adjunct to civil defense gtoups.
1-2 Station and Operator Licenses
Every radio transmitting station in the United States no matter how low its power must have a license from the federal government before being operated; some classes of stations must have a permit from the government even before being constructed. And every operator of a transmitting station must have an operators license before operating a transmitter. There are no exceptions. Similar laws apply in practically every major country.
Glosses of Amateur There are at present six Operator Licenses classes of amateur operator licenses which have been authorized by the Federal Communications Commission. These classes differ in many respects, so each will be discussed briefly.
(a) Amateur Extra Class. This class of license is available to any U. S. citizen who at any time has held for a period of two years or more a valid amateur license, issued by the FCC, excluding licenses of the Novice and Technician Classes. The examination for the license includes a code test at 20 words per minute, the usual tests covering basic amateur practice and general amateur regulations, and an additional test on advanced amateur practice. All amateur privileges are accorded the holders of this operators license.
(b) General Class, This class of amateur license is equivalent to the old Amateur Class В license, and accords to the holders all amateur privileges except those which may be set aside for holders of the Amateur Extra Class license. This class of amateur operators license is available to any U. S. citizen. The examination for the license includes a code test at 13 words per minute, and the usual examinations covering basic amateur practice and general amateur regulations.
(c) Conditional Class. This class of amateur license and the privileges accorded by it are equivalent to the General Class license. However, the license can be issued only to those whose residence is more than 125 miles airline from the nearest location at which FCC examinations ate held at intervals of not more than three months for the General Class amateur operator license, or to those who for any
of several specified reasons are unable to appear for examination.
(d) Technician Class. This is a new class of license which is available to any citizen of the United States. The examination is the same as that for the General Class license, except that the code test is at a speed of 5 words per minute. The holder of a Technician class license is accorded all authorized amateur privileges in the amateur frequency bands above 220 megacycles, and in the 50-Mc. band.
(e) Novice Class. This is a new class of license which is available to any U. S. citizen who has not previously held an amateur license of any class issued by any agency of the U. S. government, military or civilian. The examination consists of a code test at a speed of 5 words per minute, plus an examination on the rules and regulations essential to beginners operation, including sufficient elementary radio theory for the understanding of those rules. The Novice Class of license affords severely restricted privileges, is valid for only a period of one year (as contrasted to all other classes of amateur licenses which run for a term of five years), and is not renewable.
All Novice and Technician class examinations are given by volunteer examiners, as regular examinations for these two classes are not given in FCC offices. Amateur radio clubs in the larger cities have established examin ing coiranittees to assist would-be amateurs of the area in obtaining their Novice and Technician licenses.
The Amateur Bands
Certain small segments of the radio frequency spectrum between 1500 kc. and 10,000 Mc are reserved for operation of amateur radio stations. These segments are in general agreement throughout the world, although certain parts of different amateur bands may be used for other purposes in various geographic regions. In particular, the 40-meter amateur band is used legally (and illegally) for short wave broadcasting by many countries in Europe, Africa and Asia. Parts of the 80-meter band are used for short distance marine work in Europe, and for broadcasting in South America. The amateur bands available to American radio amateurs are.
160 Meters The l60-meter band is di-
(1800 KC.-2000 Kc.) vided into 25-kilocycle segments on a regional basis, with day and night power limitations, and is available for amateur use provided no interference is caused to the Loran (Long Range Navigation) stations operating in this band. This band is least affected by the 11-
year solar sunspot cycle. The Maximum Usable Frequency (MUF) even during the years of decreased sunspot activity does not usually drop below 4 Mc, therefore this band is not subject to the violent fluctuations found on the higher frequency bands. DX contacts on on this band are limited by the ionospheric absorption of radio signals, which is quite high. During winter nighttime hours the absorption is often of a low enough value to permit trans-oceanic contacts on this band. On rare occasions, contacts up to 10,000 miles have been made. As a usual rule, however, 160-meter amateur operation is confined to ground-wave contacts or single-skip contacts of 1000 miles or less. Popular before World War Ц, the l60-meter band is now only sparsely occupied since many areas of the country are blanketed by the megawatt pulses of the Loran chains.
80 Meters The 80-meter band is the
(3500 Kc.-4000 Kc.) most popular amateur band in the continental United States for local rag-chewing and traffic nets. During the years of minimum sun-spot activity the ionospheric absorption on this band may be quite low, and long distance DX contacts are possible during the winter night hours. Daytime operation, in general, is limited to contacts of 500 miles or less. During the summer months, local static and high ionospheric absorption limit long distance contacts on this band. As the sunspot cycle advances and the MUF rises, increased ionospheric absorption will tend to degrade the long distance possibilities of this band. At the peak of the sunspot cycle, the 80-meter band becomes useful only for short-haul communication.
mitters. In Europe and Asia the band is in a chaotic state, and amateur operation in this region is severely hampered.
20 Meters At the present time,
(14,000 Kc.-14,350 Kc.) the 20-meter band is by far the most popular band for long distance contacts. High enough in frequency to be almost obliterated at the bottom of the solar cycle, the band nevertheless provides good DX contacts during years of minimal sunspot activity. At the present time, the band is open to almost all parts of the world at some time during the year. During the summer months, the band is active until the late evening hours, but during the winter months the band is only good for a few hours during daylight. Extreme DX contacts are usually erratic, but the 20-meter band is the only band available for DX operation the year around during the bottom of the DX cycle. As the sunspot count increases and the MUF rises, the 20-metet band will become open for longer hours during the winter. The maximum skip distance increases, and DX contacts are possible over paths other than the Great Circle route. Signals can be heard the long paths, 180 degrees opposite to the Great Circle path. During daylight hours, absorption may become apparent on the 20-meter band, and all signals except very short skip may disappear. On the other hand, the band will be open for worldwide DX contacts all night long. The 20-meter band is very susceptible to fade-outs caused by solar disturbances, and all except local signals may completely disappear for periods of a few hours to a day or so.
40 Meters The 40-meter band is high
(7000 Kc.-7300 Kc.) enough in frequency to be severely affected by the 11-year sunspot cycle. During years of minimum solar activity, the MUF may drop below 7 Mc, and the band will become very erratic, with signals dropping completely out during the night hours. Ionospheric absorption of signals is not as large a problem on this band as it is on 80 and 160 meters. As the MUF gradually rises, the skip-distance will increase on 40 meters, especially during the winter months. At the peak of the solar cycle, the daylight skip distance on 40 meters will be quite long, and stations within a distance of 500 miles or so of each other will not be able to hold communication. DX operation on the 40-metet band is considerably hampered by broadcasting stations, propaganda stations, and jamming trans-
15 Meters This is a relatively
(21,000 Kc.-21,450 Kc.) new band for radio
amateurs since it has only been available for amateur operation since 1952. Not too much is known about the characteristics of this band, since it has not been occupied for a full cycle of solar activity. However, it is reasonable to assume that it will have characteristics similar to both the 20 and 10-meter amateur bands. It should have a longer skip distance than 20 meters for a given time, and sporadic-E (short-skip) should be apparent during the winter months. During a period of low sunspot activity, the MUF will rarely rise as high as 15 meters, so this band will be dead for a large part of the year. During the next few years, 15-meter activity
should pick up rapidly, and the band should
support extremely long DX contacts. Activity on the 15-meter band is limited in some areas.
since the older model TV receivers have a 21 Mc. i-f channel, which falls directly in the 15-meter band. The interference problems brought about by such an unwise choice of intermediate frequency often restrict operation on this band by amateur stations unfortunate enough to be situated near such an obsolete receiver.
10. Meter* During the peak of the
(28,000 Kc.-29,700 Kc.) sunspot cycle, the IOmeter band is without doubt the most popular amateur band- The combination of long skip and low ionospheric absorption make reliable DX contacts with low powered equipment possible. The great width of the band (1700 kc.) provides room for a large number of amateurs. The long skip (1500 miles or so) prevents nearby amateurs from hearing each other, thus dropping the interference level. During the winter months, sporadic-E (short skip) signals up to 1200 miles or so will be heard. The IOmeter band is poorest in the summer months, even during a sunspot maximum. Extremely long daylight skip is common on this band, and and in years of high MUF the lO-meter band will support intercontinental DX contacts during daylight hours.
The second harmonic of stations operating in the 10-meter band falls directly into television channel 2, and the higher harmonics of 10-meter transmitters fall into the higher TV channels. This harmonic problem seriously curtailed amateur 10-meter operation during the late 40s. However, with the new circuit techniques and TVI precautionary measures stressed in this Handbook, lO-meter operation should cause little or no interference to nearby television receivers of modern design.
Six Meters At the peak of the sunspot
(50 MC.-54 Mc.) cycle, the MUF occasionally rises high enough to permit DX contacts up to 10,000 miles or so on 6 meters. Activity on this band during such a period is often quite high. Interest in this band wanes during a period of lesser solar activity, as contacts, as a rule, are restricted to short-skip work. The proximity of the 6-meter band to television channel 2 often causes interference problems to amateurs located in areas where channel 2 is active. As the sunspot cycle increases, activity on the 6-meter band will increase.
The V-H-F Bands The v-h-f bands are
(Two Meters and Up ) the least affected by
the vagaries of the sunspot cycle and the Heaviside layer. Their predominant use is for reliable communication over distances of 150 miles or less. These
bands are sparsely occupied in the rural sections of the United States, but are quite heavily congested in the urban areas of high population.
In recent years it has been found that v-h-f signals are propagated by other means than by line-of-sight transmission. Scatter signals, Aurora reflection, and air-mass boundary bending are responsible for v-h-f communication up to 1200 miles or so. Weather conditions will often affect long distance communication on the 2-meter band, and all the v-h-f bands are particularly sensitive to this condition.
The other v-h-f bands have had insufficient occupancy to provide a clear picture of their characteristics. In general, they behave much as does the 2-meter band, with the weather effects becoming more pronounced on the higher frequency bands.
Starting Your Study
When you start to prepare yourself for the amateur examination you will find that the circuit diagrams, tube characteristic curves, and formulas appear confusing and difficult of understanding. But after a few study sessions one becomes sufficiently familiar with the notation of the diagrams and the basic concepts of theory and operation so that the acquisition of further knowledge becomes easier and even fascinating.
As it takes a considerable time to become proficient in sending and receiving code, it is a good idea to intersperse technical study sessions with periods of code practice. Many short code practice sessions benefit one more than a small number of longer sessions. Alternating between one study and the other keeps the student from getting stale since each type of study serves as a sort of respite from the other.
When you have practiced the code long enough you will be able to follow the gist of the slower sending stations. Many stations send very slowly when working other stations at great distances. Stations repeat their calls many times when calling other stations before contact is established, and one need not have achieved much code proficiency to make out their calls and thus determine their location.
The Code The applicant for any class of amateur operator license must be able to send and receive the Continental Code (soinetimes called the International Morse Code). The speed required for the sending and receiving test may be either 5, 13, or 20 words per minute, depending upon the class of license, assuming an average of five characters to the word in each case. The sending and re-
PERIOD (.) COMMA (,)
INTERROGATION (?) е те* QUOTATION MARK ( ) COLON () SEMICOLON (;) PARENTHESIS С )
WAITSIGNCASJ ш е
DOUBLE DASH (BREAK) ее
ERROR (ERASE SIGN) ♦ e
FRACTION BAR (/) eeeee
END OF MESSAGE Car) е в END OF TRANSMISSION (SK) INTERNAT DISTRESS SIG, (SOS) еввв-с
7Ле Confinenfo/ (or International Morse) Code is vscd for substantially all non-automatic radio communication. DO NOT memorize from the printed page; code is a language of SOUND, and must not be learned visually; learn by listening as explained in the text.
ceiving tests run for five minutes, and one minute of errorless transmission or reception must be accomplished widiin the five-minute interval.
If the code test is failed, the applicant must wait at least one month before he may again appear for another test. Approximately 30% of amateur applicants fail to pass the test. It should be expected that nervousness and excitement will at least to some degree temporarily lower the applicants code ability. The best prevention against this is to master the code at a little greater than the required speed under ordinary conditions. Then if you slow down a little due to nervousness during a test the result will not prove fatal.
Memorizing There is no shortcut to code pro-the Code ficiency. To memorize the alphabet entails but a few evenings of diligent application, but considerable time is required to build up speed. The exact time required depends upon the individuals ability and the regularity of practice.
While the speed of learning will naturally vary greatly with different individuals, about 70 hours of practice (no practice period to be over 30 minutes) will usually suffice to bring a speed of about 13 w.p.m.; 16 w.p.m. requires about 120 hours; 20 w.p.m., 175 hours.
Since code reading requires that individual letters be recognized instantly, any memorizing scheme which depends upon orderly sequence, such as learning all dah letters and all dit letters in separate groups, is to be discouraged. Before beginning with a code practice set it is necessary to memorize the whole alphabet perfectly. A good plan is to study only two or three letters a day and to drill with those letters until they become part of your consciousness. Mentally translate each days letters into their sound equivalent wherever they are seen, on signs, in papers, indoors and outdoors. Tackle two additional letters in the code chart each day, at the same time reviewing the characters already learned.
Avoid memorizing by routine. Be able to sound out any letter immediately without so much as hesitating to think about the letters preceding or following the one in question. Know C, for example, apart from the sequence ABC. Skip about among all the characters learned, and before very long sufficient letters will have been acquired to enable you to spell out simple words to yourself in dit dahs. This is interesting exercise, and for that reason it is good to memorize all the vowels first and the most common consonants пеп.
Actual code practice should start only when the entire alphabet, the numerals, period, com-
These code characters are used in languages other than English. They may occasionally be encountered so it is well to know them.
ma, and question mark have been memorized so thoroughly that any one can be sounded without the slightest hesitation. Do not bother with other punctuation or miscellaneous signals until later.
Sound - Each letter and figure must be Not Sight memorized by its sound rather than its appearance. Code is a system of sound conimunication, the same as is the spoken word. The letter A, for example, is one short and one long sound in combination sounding like dit dah, and it must be remembered as such, and not as dot dash.
Proctice Time, patience, and regularity are required to learn the code properly. Do not expect to accomplish it within a few days.
Dont practice too long at one stretch; it does more harm than good. Thirty minutes at a time should be the limit.
Lack of regularity in practice is the most common cause of lack of progress. Irregular practice is very little better than no practice at all. Write down what you have heard; then forget it; do not look back. If your mind dwells even for an instant on a signal about which you have doubt, you will miss the next few characters while your attention is diverted.
While various automatic code machines, phonograph records, etc., will give you practice, by far the best practice is to obtain a study companion who is also interested in learning the code. WЪen you have both memorized the alphabet you can start sending to each other. Practice with a key and oscillator or key and buzzer generally proves superior to all automatic equipment. Two such sets operated between two rooms are fine-or between your house and his will be just that much better. Avoid talking to your partner while practicing. If you must ask him a ques-
tion, do it in code. It makes more interesting practice than confining yourself to random practice material.
When two co-learners have memorized the code and are ready to start sending to each other for practice, it is a good idea to enlist the aid of an experienced operator for the first practice session or two so that they will get an idea of how properly formed characters sound.
During the first practice period the speed should be such that substantially solid copy can be made without strain. Never mind if this is only two or three words per minute. In the next period the speed should be increased slightly to a point where nearly all of the characters can be caught only through conscious effort. When the student becomes proficient at this new speed, another slight increase may be made, progressing in this manner until a speed of about 16 words per minute is attained if the object is to pass the amateur 13-word per minute code test. The margin of 3 w.p.m. is recommended to overcome a possible excitement factor at examination time. Then when you take the test you dont have to worry about the jitters or an off day.
Speed should not be increased to a new level until the student finally makes solid copy with ease for at least a five-minute period at the old level. How frequently increases of speed can be made depends upon individual ability and the amount of practice. Each increase is t to prove disconcerting, but remember you are never learning when you are comfortable.
A number of amateurs are sending code practice on the air on schedule once or twice each week; excellent practice can be obtained after you have bought or constructed your receiver by taking advantage of these sessions.
If you live in a medium-size or large city, the chances are that there is an amateur radio club in your vicinity which offers free code practice lessons periodically.
Skill When you listen to someone speaking you do not consciously think how his words are spelled. This is also true when you read. In code you must train your ears to read code just as your eyes were trained in school to read printed matter. With enough practice you acquire skill, and from skill, speed. In other words, it becomes a habit, something which can be done without conscious effort. Conscious effort is fatal to speed; we cant think rapidly enough; a speed of 25 words a minute, which is a common one in commercial operations, means 125 characters per minute or more than two per second, which leaves no time for conscious thinking.
Perfect Formation When transmitting on the of Chorocters code practice set to your
partner, concentrate on the quality of your sending, not on your speed. Your partner will appreciate it and he could not copy you if you speeded up anyhow.
If you want to get a reputation as having an excellent fist on the air, just remember that speed alone wont do the trick. Proper execution of your letters and spacing will make much more of an impression. Fortunately, as you get so that you can send evenly and accurately, your sending speed will automatically increase- Remember to try to see how evenly you can send, and how fast you can receive. Concentrate on making signals properly with your key. Perfect formation of characters is paramount to everything else. Make every signal right no matter if you have to practice it hundreds or thousands of times. Never allow yourself to vary the slightest from perfect formation once you have learned it.
If possible, get a good operator to listen to your sending for a short time, asking him to criticize even the slightest imperfections.
Timing It is of the utmost importance to maintain uniform spacing in characters and combinations of characters. Lack of uniformity at this point probably causes beginners more trouble than any other single factor. Every dot, every dash, and every space must be correctly timed. In other words, accurate timing is absolutely essential to intelligibility, and timing of the spaces between the dots and dashes is just as important as the lengths of the dots and dashes themselves.
The characters are timed with the dot as a yardstick, A standard dash is three times as long as a dot. The spacing between parts of the same letter is equal to one dot; the space between letters is equal to three dots, and that between words equal to five dots.
The rule for spacing between letters and words is not strictly observed when sending slower than about 10 words per minute for the benefit of someone learning the code and desiring receiving practice. When sending at, say, 5 w.p.m., the individual letters should be made the same as if the sending rate were about 10 w.p.m., except that the spacing between letters and words is greatly exaggerated. The reason for this is obvious. The letter L, for instance, will then sound exactly the same at 10 w.p.m. as at 5 w.p.m., and when the speed is increased above 5 w.p.m. the student will not have to become familiar with what may seem to him like a new sound, although it is in reality only a faster combination of dots and dashes. At the greater speed he will merely have to learn the identification of the same sound without taking as long to do so.
m 1 !
Diagram illustrating relative lengths of dashes and spaces referred to the duration of a dot. A dash is exactly equal in duration to three dots; spaces between parts of a letter equal one dot; those between letters, three dots; space between words, five dots. Note that a slight increase between two parts of a letter will make it sound like two letters.
Be particularly careful of letters like B. Many beginners seem to have a tendency to leave a longer space after the dash than that which they place between succeeding dots, thus making it sound like TS, Similarly, make sure that you do not leave a longer space after the first dot in the letter С than you do between other parts of the same letter; otherwise it will sound like NN.
Sending vs. Once you have memorized the Receiving code thoroughly you should concentrate on increasing your receiving speed. True, if you have to practice with another newcomer who is learning the code with you, you will both have to do some sending. But dont attempt to practice sending just for the sake of increasing your sending speed.
When transmitting on the code practice set to your partner so that he can get receiving practice, concentrate on the quality of your sending, not on your speed.
Because it is comparatively easy to learn to send rapidly, especially when no particular care is given to the quality of sending, many operators who have just received their licenses get on the air and send mediocre or worse code at 20 w.p.m. when they can barely receive good code at 13. Most oldtimers remember their own period of initiation and are only too glad to be patient and considerate if you tell them that you are a newcomer. But the surest way to incur their scorn is to try to impress them with your lightning speed, and then to request them to send more slowly when they come back at you at the same speed.
Stress your copying ability; never stress your sending ability, yit should be obvious that
that if you try to send faster than you can receive, your ear will not recognize any mistakes which your hand may make.
fingers to become tense. Send with a full, free arm movement. Avoid like the plague any finger motion other than the slight cushioning effect mentioned above.
Stick to the regular hand key for learning code. No other key is satisfactory for this purpose. Not until you have thoroughly mastered both sending and receiving at the maximum speed in which you are interested should you tackle any form of automatic or semi-automatic key such as the Vibroplex ( bug ) or an electronic key.
PROPER POSITION OF THE FINGERS FOR OPERATING A TELEGRAPH KEY
The fingers hold the knob and act as a cushion. The hand rests lightly on the key. The muscles of the forearm provide the power, the wrist acting as the fulcrum. The power should not come from the fingers, but rather from the forearm muscles.
Using the Key Figure 4 shows the proper position of the hand, fingers and wrist when manipulating a telegraph or radio key. The forearm should rest naturally on the desk. It is preferable that the key be placed far enough back from the edge of the table (about 18 inches) that the elbow can rest on the table. Otherwise, pressure of the table edge on the arm will tend to hinder the circulation of the blood and weaken the ulnar nerve at a point where it is close to the surface, which in turn will tend to increase fatigue considerably.
The knob of the key is grasped lightly with the thumb along the edge; the index and third fingers rest on the top towards the front or far edge. The hand moves with a free up and down motion, the wrist acting as a fulcrum. The power must come entirely from the arm muscles. The third and index fingers will bend slightly during the sending but not because of deliberate effort to manipulate the finger muscles. Keep your finger muscles just tight enough to act as a cushion for the arm motion and let the slight movement of the fingers take care of itself. The keys spring is adjusted to the individual wrist and should be neither too stiff nor too loose. Use a moderately stiff tension at first and gradually lighten it as you become more proficient. The separation between the contacts must be the proper amount for the desired speed, being somewhat under 1/16 inch for slow speeds and slightly closer together (about 1/32 inch) for faster speeds. Avoid extremes in either direction.
Do not allow the muscles of arm, wrist, or
Difficulties Should you experience difficulty in increasing your code speed after you have once memorized the characters, there is no reason to become discouraged. It is more difficult for some people to learn code than for others, but there is no justification for the contention sometimes made that some people just cant learn the code. It is not a matter of intelligence; so dont feel ashamed if you seem to experience a little more than the usual difficulty in learning code. Your reaction time may be a little slower or your coordination not so good. If this is the case, remember you can still learn the code. You may never learn to send and receive at 40 w.p.m., but you can learn sufficient speed for all non-commercial рифовев and even for most commercial purposes if you have patience, and refuse to be discouraged by the fact that others seem to pick it up more rapidly.
When the sending operator is sending just a bit too fast for you (the best speed for practice), you will occasionally miss a signal or a small group of them. When you do, leave a blank space; do not spend time futilely trying to recall it; dismiss it, and center attention on the next letter; otherwise youll miss more. Do not ask the sender any questions until the transmission is finished.
To prevent guessing and get equal practice on the less common letters, depart occasionally from plain language material and use a jumble of letters in which the usually less commonly used letters predominate.
As mentioned before, many students put a greater space after the dash in the letter В than between other parts of the same letter so it sounds like TS. C, F, Q. V, X, Y and Z often give similar trouble. Make a list of words or arbitrary combinations in which these letters predominate and practice them, both sending and receiving until they no longer give you trouble. Stop everything else and stick at them. So long as they give you trouble you are not ready for anything else.
Follow the same procedure with letters which you may tend to confuse such as P and L, which are often confused by beginners.
THE SIMPLEST CODE PRACTICE SET CONSISTS OF A KEY AND A BUZZER
The buzzer is adjusted to give a steady, high-pitched whine. If desired, the phones may be omitted, in which case the buzzer should be mounted firmly on a sounding board. Crystal, magnetic, or dynamic earphones may be used. Additional sets of phones should be connected in parallel, not in series.
1.5 TO 4.5 VOLTS OF BATTERY
INEXPENSIVE 500 OHM POTENTIOMETER --t VOLUME CONTROL
PHONES, 1 TO 4 PAIR
THESE PARTS REQUIRED ONLY IF HEADPHONE OPERATION IS DESIRED
Keep at it until you always get them right without having to stop even an instant to think about it.
If you do not instantly recognize the sound of any character, you have not learned it; go back and practice your alphabet further. You should never have to omit writing down every signal you hear except when .the transmission is too fast for you.
Write down what you hear, not what you think it should be. It is suфrising how often the word which you guess will be wrong.
Copying Behind All good operators copy several words behind, diat is, while one word is being received, they are writing down or typing, say, the fourth or fifth previous word. At first this is very difficult, but after sufficient practice it will be found actually to be easier than copying close up. It also results in more accurate copy and enables the receiving operator to capitalize and
10 к 0.5W
2000 SX PHONES
SIMPLE TRANSISTOR CODE PRACTICE OSCILLATOR
An inexpensive Raytheon CK722 transistor requires only a single IA-volt flashlight battery for power. The inductance of the earphone windings forms part of the oscillotory
circuit. The pitch af the nofe may be changed
by varying the value af the two capacitors connected across the earphones.
punctuate copy as he goes along. It is not recommended that the beginner attempt to do this until he can send and receive accurately and with ease at a speed of at least 12 words a minute.
It requires a considerable amount of training to dissociate the action of the subconscious mind from the direction of the conscious mind. It may help some in obtaining this training to write down two columns of short words. Spell the first word in the first column out loud while writing down the first word in the second column. At first this will be a bit awkward, but you will rapidly gain facility with practice. Do the same with all the words, and then reverse columns.
Next try speaking aloud the words in the one column while writing those in the other column; then reverse columns.
After the foregoing can be done easily, try sending with your key the words in one column while spelling those in the other. It wont be easy at first, but it is well worth keeping after if you intend to develop any real code proficiency. Do not attempt to catch up. There is a natural tendency to close up the gap, and you must train yourself to overcome this.
Next have your code companion send you a word either from a list or from straight text; do not write it down yet. Now have him send the next word; after receiving this second word, write down the first word. After receiving the third word, write the second word; and so on. Never mind how slowly you must go, even if it is only two or three words per minute. Stay behind.
It will probably take quite a number of practice sessions before you can do this with any facility. After it is relatively easy, then try staying two words behind; keep this up until it is easy. Then try three words, four words, and five words. The more you practice keeping received material in mind, the easier it will be to stay behind. It will be found easier at first to copy material with which one is fairly familiar, then gradually switch to less familiar material.
Automatic Code The two practice sets which Mochines are described in this chapter
are of most value when you have someone with whom to practice. Automatic code machines are not recommended to anyone who can possibly obtain a companion with whom to practice, someone who is also interested in learning the code. If you are unable to enlist a code partner and have to practice by yourself, the best way to get receiving practice is by the use of a tape machine (automatic code sending machine) with several practice tapes. Or you can use a set of phonograph code practice records. The records are of use only if you have a phonograph whose turntable speed is readily adjustable. The tape machine can be rented by the month for a reasonable fee.
Once you can copy about 10 w.p.m. you can also get receiving practice by listening to slow sending stations on your receiver. Many amateur stations send slowly particularly when working far distant stations. When receiving conditions are particularly poor many commercial stations also send slowly, sometimes repeating every word. Until you can copy around 10 w.p.m. your receiver isnt much use, and either another operator or a machine or records are necessary for getting receiving practice after you have once memorized the code.
Code Practice Sets
If you dont feel too foolish doing it, you can secure a measure of code practice with
the help of a partner by sending dit-dah messages to each other while riding to work, eating lunch, etc. It is better, however, to use a buzzer or code practice oscillator in conjunction with a regular telegraph key.
As a good key may be considered an investment it is wise to make a well-made key your first purchase. Regardless of what type code practice set you use, you will need a key, and later on you will need one to key your transmitter. If you get a good key to begin with, you wont have to buy another one later.
The key should be rugged and have fairly heavy contacts. Not only will the key stand up better, but such a key will contribute to the heavy type of sending so desirable for radio work. Morse (telegraph) operators use a light style of sending and can send somewhat faster when using this light touch. But, in radio work static and interference are often present, and a slightly heavier dot is desirable. If you use a husliy key, you will tind yourself automatically sending in this manner.
To generate a tone simulating a code signal as heard on a receiver, either a mechanical buzzer or an audio oscillator may be used. Figure 5 shows a simple code-practice set using a buzzer which may be used directly simply by mounting the buzzer on a sounding board, or the buzzer may be used to feed from one to four pairs of conventional high-impedance phones.
An example of the audio-oscillator type of code-practice set is illustrated in figures 6 and 7. An inexpensive Raytheon CK-722 transistor is used in place of the more expensive, power consuming vacuum tube. A single pen-lite l!4-volt cell powers the unit. The coils of the earphones form the inductive portion of the resonant circuit. Phones having an impedance of 2000 ohms or higher should be used. Surplus type R-14 earphones also work well with this circuit.
The circuit of Figure 6 is used in this miniature transistorized code Practice oscillator. Components are mounted in a small plastic case. The transistor is attached to a three terminal phenol ic mounting strip. Sub-miniature /aclis ore used for the key and phones connections. A bearing aid earphone may also be used, as shown. The phone is stored In the plastic case when not in use.
1 2 3 4 ... 80
© 2022 AutoElektrix.ru
Частичное копирование материалов разрешено при условии активной ссылки