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Saturday, August 10, 2013

1965 Ham License Answers

Novice:
  1. Question #9: What method of frequency control is required to be used in the transmitter of a station licensed to the holder of a Novice Class License? The frequency must be crystal-controlled.
  2. Question #13: What is the maximum permissible percentage of modulation of an amateur radiotelephone station? 100%
  3. Question #17: What is the relationship between a fundamental frequency and its second harmonic; its third harmonic, etc.? The second harmonic is twice the frequency of the fundamental, the third harmonic is three times the fundamental frequency, and so on. A harmonic is always related to its fundamental frequency by an integral multiplier; i.e., 2, 3, 4, 5, 6, etc.
  4. Question #23: How is the actual power input to the tube or tubes supplying energy to the antenna of an amateur transmitter determined? The input power is determined by measuring the direct-current plate oltage and the d.c. plate current to the tubes in the final stage in the transmitter. The power input is equal to the plate voltage multiplied by the plate current in amperes.
  5. Question #27: What is meant by a "parasitic" oscillation? A parasitic oscillation is one not essential to the operation of the equipment and usually occurring on a frequency considerably removed from the operating frequency.
General:
  1. Question #1: Name the basic units of:
    • electrical resistance - ohm
    • inductance - henry
    • capacitance - farad
    • current - ampere
    • electromotive force or potential difference - volt (electromotive force is a fancy term for "voltage")
    • power - watt
    • energy - joule
    • quantity - coulomb
    • magneto-motive force - gilbert
    • frequency - cycles-per-second, or cycles (nowadays known as "hertz")
     
  2. Question #10: What is the principal reason for using a filter in a plate power-supply system? The principal reason for using a filter in a plate power-supply system is to smooth out the a.c. ripple component in the output and make it "pure d.c."
  3. Question #19: What undesirable effects may result from operation of an unneutralized triode r.f. amplifier in a transmitter? Self-oscillation may result, with consequent radiation on undesired frequencies, possibly outside an amateur band.
  4. Question #69: What is meant by a "doubler" stage? A vacuum-type circuit in which the output circuit is tuned to twice or doube the frequency of the input circuit.
  5. Question #71: What is the reciprocal of resistance? Conductance, measured in mhos ("ohms" spelled backwards)
  6. Question #106: What precaution should be taken to protect filter capacitors connected in series? Resistors having a value of approximately 100,000 ohms should be shunted across each capacitor to equalize the d.c. voltage drops and thus prevent breakdown of the individual capacitors.
Extra:
  1. Question #4: What factors determine the core losses in a transformer? Core losses are one of two types, hysteresis and eddy-current losses. Hysteresis losses vary with the type and volume of iron or steel used in the core and with the operating frequency and magnetic flux density. Eddy-current losses vary with the volume and resistance of the core material, the thickness of the laminations, and frequency and the flux density.
  2. Question #7: In a Class-C r.f. amplifier, what ratio of load impedance to dynamic plate impedance will give the greatest plate efficiency? The highest possible load impedance will give the greatest efficiency, since the ratio of the power in the load to power lost in the plate becomes larger as the ratio of load impedance is increased. However, under these conditions, the power output is relatively small.
  3. Question #12: During 100 percent sinusoidal amplitude modulation, what percentage of the average output power is in the sidebands? 33 1/3% The average power output would increase 50% with such modulation; i.e., a 100-watt unmodulated carrier output would rise to 150 watts. Sidebands carry the excess of 50 watts, which is 1/3 the total.
  4. Question #25: What are synchronizing pulses as used in television transmitters and receivers? Synchronizing pulses used in television transmitters and receivers are pulses of extremely short duration which ensure that trace lines across the face of the picture tube in the receiver are synchronized with the trace lines in the television camera.
  5. Question #34: What determines the operating frequency of a magnetron oscillator? Its dimensions and the electric and magnetic field intensities; also, the associated circuit constants.
  6. Question #46: If the conductors in a 2-wire r.f. transmission line are replaced by larger conductors, how is the surge impedance affected, assuming no change in the center-to-center spacing of the conductor? The surge impedance is lowered.
  7. Question #63: What is the purpose of the mosaic plate in a television camera? To what item of photographic equipment is it similar in function? To store an electrical image corresponding to the visual image focused upon it, for later scanning by an electron beam to translate the electrical image into a television signal. Its function is similar to that of the film in a photographic camera, which similarly stores the image for later development.
  8. Question #92: What are the "Baudot" and "Seven Unit" codes? How are they used? Both are used in teleprinter operation. Baudot used with synchronous printers, 7-unit with start-stop printers. Each transmitted character has assigned to it a fixed time interval divided into units, 5 for Baudot and 7 for 7-unit teletype. A particular character is distinguished by a unique combination of mark and space units in that particular codes being used in all cases.
  9. Question #120: What is the meaning of the term "frequency swing" in reference to frequency-modulation transmitters? The peak difference between the maximum and minimum values of the instantaneous frequency.
  10. Question #136: What is the ohms per volt of a voltmeter constructed of a 0-1 d.c. milliammeter and a suitable resistor which makes the full-scale reading of the meter 500 volts? 1000 ohms per volt.
  11. Question #181: What is meant by low-level modulation? That applied to an early or intermediate stage of a transmitter (instead of to the final amplifier) i.e., at a point where the power level is comparatively low.
  12. Question #204: State where antenna impedance is usually measured. At the point where the antenna is fed. The value so measured is frequently converted into an equivalent value at a current loop.
  13. Question #219: Define a "back-wave" and explain what causes it. A signal emitted during key-up conditions. In make-break keying, it may be caused by energy from unkeyed exciter stages leaking through a keyed amplifier (because of improper neutralizations, etc.) or by parasitic oscillation. In frequency-shift keying the "space" signal in the back-wave.