License Exam Quiz #317

The inspiration for this week’s quiz is Johann Carl Friedrich Gauss, born 30 April 1777 in Braunschweig, Germany. The Gaussian distribution is probably the first thing people will recognize, and that does have relevance to radio in modeling thermal noise, signal processing, and information theory. Gauss also developed the Method of Least Squares (linear regression) which is useful for identifying signal strength and direction, and so has application in RADAR and direction finding. Working with Wilhelm Weber, they explored magnetism and electricity building one of the first electromagnetic telegraphs and laying down some of the theory and experimental groundwork that would later influence James Clerk Maxwell and the understanding of radio wave propagation. (Weber, has a unit of measure named for him, we should probably make him a quiz inspiration...October!) Gauss’s Law helps describe electric fields, capacitive behavior, and the design and analysis of antennas. Gauss also performed work in the area of number theory, modular arithmetic, and quadratic residues which today are used in things such as phase-shift keying, error correction, and spread spectrum radio communication. Satellites, GPS, radio-astronomy, we could go on but let’s get to some questions!

T4B07 What does a DMR “code plug” contain?

A. Your call sign in CW for automatic identification

B. Access information for repeaters and talkgroups

C. The codec for digitizing audio

D. The DMR software version

G3C03 Why is skip propagation via the F2 region longer than that via the other ionospheric regions?

A. Because it is the densest

B. Because of the Doppler effect

C. Because it is the highest

D. Because of temperature inversions

E8D01 Why are received spread spectrum signals resistant to interference?

A. Signals not using the spread spectrum algorithm are suppressed in the receiver

B. The high power used by a spread spectrum transmitter keeps its signal from being easily overpowered

C. Built-in error correction codes minimize interference

D. If the receiver detects interference, it will signal the transmitter to change frequencies

Answers:

T4B07 = B (Modular arithmetic is foundational to error correction)

G3C03 = C (Electromagnetism, a stepping stone for Maxwell’s work)

E8D01 = A (Primitive roots, modular arithmetic, quadratic residues contribute to pseudorandom number generators, linear feedback shift registers, and spreading codes.)