By H. Ward Silver. N0AX
[email protected]

Amateur Radio deals with everything -- from the very, very small to the very, very large -- so it’s particularly important that we know how to work with units of measurement. One of the easiest checks on a calculation is whether the units “work out” they way you expect. To do that requires a certain facility with units, constants and conversion factors -- and no calculator can help you with that! Here’s an opportunity to poke around in your unitary toolbox and see if you recognize some of the pieces there.

1) How big is an Angstrom?
a. 0.1 nanometer
b. 10 nanometers
c. 1 micro-inch
d. 1 milli-millimeter

2) How big is a micron?
a. 1 millionth of a centimeter
b. 1 millionth of a meter
c. 10 angstroms
d. 100 angstroms

3) Which metric prefix represents the largest value?
a. tera
b. exa
c. femto
d. peta

4) Which metric prefix represents the smallest value?
a. atto
b. nano
c. zetta
d. deka

5) Which two of the following are used to calculate the impedance of free space to electromagnetic waves?
a. permeability
b. permittivity
c. porosity
d. permeance

6) A “googol” refers to ten raised to what power?
a. 99
b. 100
c. 101
d. 1000

7) In the equation for thermal noise -- kTB -- what does “k” represent?
a. Constant of Integration
b. Degrees Kelvin
c. Boltzmann’s Constant
d. Planck Length

8) Which of the following is used for power measurements?
a. dBd
b. dBi
c. dBm
d. dBV

9) Rank these units of energy from the smallest to the largest.
a. kW-hr
b. erg
c. BTU
d. Joule

10) What is the unit for transmitted symbols or transitions per second?
a. bits
b. baud
c. bel
d. ber

Bonus Question: Which electrical unit was originally spelled backwards from its complementary unit?

Answers
1. A
2. B
3. b -- 1018
4. a -- 10-18
5. a and b -- the impedance of a medium equals the square root of the ratio of its permeability to permittivity
6. B
7. C -- More accurately known as the Stefan-Boltzmann Constant
8. c -- decibels with respect to 1 mW
9. b - d - c – a
10. b

Bonus: The mho was the unit of conductance -- the complement of resistance -- but has been replaced by the siemens.