1. Radio Math Notes For FCARC Technician License Class Session 2b
April 11, 2013

2. The decibel (dB) is a logarithmic unit that indicates the ratio of a physical quantity (usually power or intensity) relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities.[1] A decibel is one tenth of a bel, a seldom-used unit named in honor of Alexander Graham Bell.
A change in power ratio by a factor of 10 is a 10 dB change. A change in power ratio by a factor of two is approximately a 3 dB change.
Source: Wikipedia

3. dB power ratio amplitude ratio
(~2)
(~2)
(~1/2)
(~1/2)

4. There are several different mathematical relationships you will be expected to know how to use to pass the Technician license exam
Voltage, current and resistance (Ohm's Law)
Voltage, current, and power
Wavelength, frequency, and speed of light

5. All of these involve three quantities.
So if you know how to deal with a relationship
like A=B*C
you should be able to deal with all of these.
Not everyone learns things the same way....

6. For some people the easiest thing is to memorize all of the possible combinations:
A=B*C
B=A/C
C=A/B

7. A mathematician would think it through like this:

8. To get B all alone first switch the sides: B*C = A
Start with this: A = B*C
To get B all alone first switch the sides:
B*C = A
divide both sides by C
(B*C)/C = A/C
But C/C = 1, so Cs on the left cancel
B = A/C
You can get the formula for C the same way

9. Some find a visual memory clue helps:
In the circle choose
one symbol to put on
the left of the “=” and
the other symbols will
be in the correct
relationship

10. A = B * C
B = A / C
C = A / B

11. Ohm's Law
E= I*R
I=E/R
R= E/I
Power
P= I*E
E=P/I
I=P/E
Frequency &Wavelength
c=L*f
L=c/f
f=L/c

12. Sometimes physical intuition is what helps you remember:
Obviously if resistance increases, you need more
voltage to get the same amount of current

13. Sometimes physical intuition helps you remember:
If resistance increases, you need to push harder (more voltage) to get the same amount of current
E= I*R

14. Here are a couple of other things to help you remember....

15. Some prefixes Watts Kilowatts Megawatts Gigawatts Who Killed Mother
Goose?

16. International System of Units
( SI from French: Le Système international d'unités)

17. More prefixes