A Few Constants of Interest
Note: Values in bold are exact.
| Name |
Symbol
|
Value
|
Unit
|
| Astronomical Unit |
|
1.49598E+11 |
meter |
| Base of natural logs |
e |
2.71828182845904 |
- -
|
| Degree of longitude at equator |
- -
|
68.703
|
miles (statute) |
| Degree of latitude @ 40 degrees |
- -
|
69
|
miles (statute) |
| Pi |
p
|
3.141592653589879
|
- -
|
| Radius of the Earth, Equatorial |
- -
|
6,378.388
|
kilometers
|
| Radius of the Earth, Equatorial |
- -
|
3,963.34
|
miles (statute) |
| Radius of the Earth, Polar |
- -
|
6,356.912
|
kilometer |
| Radius of the Earth, Polar |
- -
|
3,949.99
|
miles (statute)
|
| Sound Velocity in Dry Air @ 0 Deg.C |
- -
|
1,087.1
|
feet/second
|
| Sound Velocity in Dry Air @ 0 Deg.C |
- -
|
331.36
|
meters/second
|
| Speed of light in a vacuum |
c
|
299,792,458
|
meters/second
|
Note: Information on all constants in numerous categories is available at the NIST Reference on Constants, Units and Uncertainty. (NIST = the National Institute of Science and Technology.)
Ohm's Law
| Formula |
|
Notes:
|
| E = I x R |
|
Where: |
I = E / R
|
|
E = EMF in Volts
|
R = E / I
|
|
I = Current in Amperes |
P = I2R
|
|
R = Resistance in Ohms |
| P = V2/R |
|
P = Power in Watts |
Power Conversions
| Description |
Formula
|
|
Notes |
| Watts to dBm: |
dBm = 10 x Log10 [Watts x 103] |
|
Where: |
| dBm to milliWatts: |
mW = 10(dBm/10) |
|
dBm = Decibels referenced one milliwatt |
| dBm to Watts: |
W =10(dBm/10)/100
|
|
W = Watts; mW = milliWatts
|
| |
|
|
|
dB Correction Factor
To correct the dB reading when the measured impedance is different from the meter's basis of calibration:
1.) dBCF = 10log(Calibration Ω / load Ω)
2.) dBActual = dBMeter + dBCF
Where:
dBCF = Correction factor
Ω = Impedance in ohms
Frequency and Wavelength Conversions
| Formula |
|
Notes:
|
λm = 299,792.458 / fkHz
|
|
|
| λm = 299.792458 / fmHz |
|
Where: |
| λft = 983,571.056430446 / fkHz |
|
λm = Wavelength in meters
|
| λft = 983.571056430446 / fmHz |
|
λft = Wavelength in feet
|
| fkHz = 299,792.458 / λm |
|
fkHz = Frequency in kiloHertz
|
| fmHz = 299.792458 / λm |
|
fmHz = Frequency in megaHertz
|
| fkHz = 983,571.056430446 / λft |
|
|
| fmHz = 983.571056430446 / λft |
|
|
Free Space Attenuation
| Formula |
|
Notes: |
a = 96.6 + 20log10 FGHz + 20log10 Dmi
|
|
Where: |
| a = 36.6 + 20log10 FMHz + 20log10 Dmi |
|
a = Attenuation in dB
|
| a = 32.45 + 20log10 FMHz + 20log10 Dkm |
|
FGHz = Frequency in GHz |
| |
|
FMHz = Frequency in MHz |
| |
|
Dmi= Path distance in miles |
| |
|
Dkm = Path distance in kilometers
|
Line-Of-Sight
| Description |
Formula
|
|
Notes:
|
| Optical Line of Sight |
D = 0.866(v2hTX + v2hRX ) |
|
Where: |
| |
|
|
D = Distance in miles |
| Radio Line of Sight (4/3 Earth) |
D = v2hTX + v2hRX
|
|
hTX = Height of the Transmitting Antenna in Feet
|
| |
|
|
hRX = Height of the Receiving Antenna in Feet
|
|
|
