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Answers to RF Cafe Quiz #10

All RF Cafe quizzes would make perfect fodder for employment interviews for technicians or engineers - particularly those who are fresh out of school or are relatively new to the work world. Come to think of it, they would make equally excellent study material for the same persons who are going to be interviewed for a job.

Click here for the complete list of RF Cafe Quizzes.

Note: Many answers contain passages quoted in whole or in part from the text.

Return to RF Cafe Quiz #10

1. What format would a near-filed communications (13 MHz variety) antenna most likely take?

a) Inductive coil.

Most devices on the market today use an inductive coil to exploit the principle of magnetic induction whereby a current-carrying conductor in motion relative to another conductor induces a similar current.

2. What does SOLT stand for?

c) Short, Open, Load, Through.

In order to perform a full 2—port calibration on a vector network analyzer (VNA), it is necessary to calibrate with both test cables using a certified set of adapters and terminations that meet industry specifications. The VNA then calculates the set of 12 error correction terms necessary to subtract out the effects of the system, including the test cables.

3. Which instrument would be best to use to locate a defective waveguide joint?

d) Time Domain Reflectometer (TDR).

The TDR sends a pulse of energy down the line and measures the length of time the reflected signal takes to return. A region of poor VSWR will reflect a portion of the signal energy that is dependent upon the degree of mismatch. If the entire length of waveguide and the termination are properly matched, there will be no returned (reflected) signal. Many network analyzers have this built-in capability.

4. Which entity in the U.S. determines whether an RF energy-emitting device is allowed to be operated?

a) The Federal Communications Commission (FCC).

Whether the radiation be intentional or unintentional, all products for commercial and private use must pass emissions testing as specified by the FCC.

5. What does 2G, 2.5G, 3G, etc., mean in reference to cellphones?

b) The “generation” of the technology.

1G was the original analog phones. 2G introduced digital technology. 3G ushered in high bandwidth data along with voice, but it was late to arrive, so 2.5G filled the gap. 4G is now in the works.

6. Where would you be likely to find a free wireless Internet connection?

d) All the above.

"a" and '"b" are obvious. See my Kirt's Cogitation for "c."

7. Who hosts the MTT-S International Microwave Symposium?

d) The Institute of Electrical and Electronics Engineers (IEEE).

Since 1958, the IEEE Microwave Theory and Techniques Society (MTT-S), has put on the show.

8. What is the “rule of thumb” for estimating RF signal propagation distance vs. time in free space?

c) 1 foot per nanosecond.

Electromagnetic energy travels about one foot in one
nanosecond in free space (actually 1.01670336 ns), and in one nanosecond, it travels about one foot (actually 0.98357106 ft). The other three choices do not produce such close approximations (1 mm = ,3.3 ps, 1 m = 3.3 ns, 1 in = 85 ps).

9. What is the “rule of thumb” for estimating RF frequency vs. wavelength in free space?a) 300 MHz = 1 meter.
More precisely, 300 MHz has a wavelength of 0.999308193 meters, but the error is about 0.07% - close enough. 100 MHz ≈ 3 m, 300 MHz ≈ 3.28 ft, 100 MHz ≈ 9.84 ft.

10. What is the most unique feature of a Helmholtz coil?

b) Magnetic field lines are extremely uniform within the coil.

This property makes the Helmholtz coil configuration very useful when testing magnetic properties since a device under test can be placed within the coil to free it from influences of outside magnetic field variations. If you chose “A,” you are thinking of a Tesla Coil.

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