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Useful Bits of Information

Decibels | Capacitor Self Resonance | Electric Field Levels| Rise Times-Frequency-Length | Frequency-Wavelength-Skin Depth | CISPR 22 Limits

Decibels

dB Power
Ratio		 Voltage
Current
Ratio		 dB Power
Ratio		 Voltage
Current
Ratio
0 1.0 1.0 0 1.0 1.0
3 2.0 1.4 -3 0.50 0.71
6 4.0 2.0 -6 0.25 0.50
10 10.0 3.2 -10 0.10 0.32
12 16.0 4.0 -12 0.05 0.25
14 25.0 5.0 -14 0.04 0.20
20 10E2 10 -20 10E-2 0.10
30 10E3 32 -30 10E-3 0.03
40 10E4 10E2 -40 10E-4 10E-2
60 10E6 10E3 -60 10E-6 10E-3
80 10E8 10E4 -80 10E-8 10E-4
100 10E10 10E5 -100 10E-10 10E-5
120 10E12 10E6 -120 10E-12 10E-6
140 10E14 10E7 -140 10E-14 10E-7

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Capacitor Self Resonance

 
Total Lead Length
  1/4" 1/2" 1"
500 pf 100 MHz 72 MHz 50 MHz
1000 pf 72 51 36
0.01 uf 23 16 11
0.1 uf 7.2 5.1 3.6
0.3 uf 4.2 2.9 2.1
0.5 uf 3.2 2.3 1.6

fo = 1/2p*sqrt(LC)

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Electric Field Levels

  1 m 10 m 100 m 1 km 10 km
1 W 5.5 V/m 0.55 V/m 55 mV/m 5.5 mV/m 0.55 mV/m
10 W 17.4 V/m 1.7 V/m 170 mV/m 17 mV/m 1.7 mV/m
100 W 55 V/m 5.5 V/m 550 mV/m 55 mV/m 5.5 mV/m
1 kW 174 V/m 17 V/m 1.7 V/m 170 mV/m 17 mV/m
10 kW 550 V/m 55 V/m 5.5 V/m 550 mV/m 55 mV/m
100 kW 1.74 kV/m 174 V/m 17 V/m 1.7 V/m 170 mV/m
1 MW 5.5 kV/m 550 V/m 55 V/m 5.5 V/m 550 mV/m

E = 5.5*SQRT (PA)/d, Electric Field in V/m
P = Power at Antenna in watts
A = Antenna Gain (assumed = 1 in Table)
d = Distance from Antenna in meters (for d > l/2p)

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Rise Times - Frequency - Length

tr feq Lcross Lcross/2 Lterm
0.1 nsec 3.2 GHz 1.2 in 0.6 in 0.3 in
0.3 nsec 950 MHz 4 in 2 in 1 in
1 nsec 318 MHz 1.0 ft 6 in 3 in
3 nsec 95 MHz 3.0 ft 1.5 ft 9 in
10 nsec 32 MHz 10 ft 5 ft 2.5 ft
30 nsec 9.5 MHz 30 ft 15 ft 7.5 ft
100 nsec 3.2 MHz 100 ft 50 ft 25 ft
300 nsec 950 KHz 300 ft 150 ft 75 ft
1 usec 320 KHz 1000 ft 500 ft 250 ft

tr = rise time
feq = equivalent frequency (1/ptr)
Lcross = length of one rise time in free space
Lcross/2 = typical length of rise time on cable or printed circuit board (crosstalk)
Lterm = length to terminate on cable or printed circuit board
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Frequency vs Wavelength

F

l

l/2p

l/20
10 Hz 30,000 KM 4,800 KM 1,500 KM
60 Hz 5,000 KM 800 KM 250 KM
100 Hz 3,000 KM 480 KM 150 KM
400 Hz 750 KM 120 KM 37 KM
1 KHz 300 KM 48 KM 15 KM
10 KHz 30 KM 4.8 KM 1.5 KM
100 KHz 3 KM 480 M 150 M
1 MHz 300 M 48 M 15 M
10 MHz 30 M 4.8 M 1.5 M
100 MHz 3 M 0.48 M 15 CM
1 GHz 30 CM 4.8 CM 1.5 CM
10 GHz 3 CM 4.8 MM 1.5 MM

F = Frequency
l = Wavelength
l/2p = Near Field to Far Field Distance
l/20 = Antenna Effects of Wires and Slots
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CISPR 22 Limits

Radiated

Quasi-

Peak

 FREQ (MHz)

Class A

Class B
30-230 40 dBmv/m 30 dBmv/m
230-1000 47 dBmv/m 37 dBmv/m
 
Conducted

Average

 0.15-50 66 dBmv 56 to 46dBmv

0.50-5

 60 dBmv 46 dBmv

5-30

 60 dBmv 50 dBmv

For equivalent values at 3 meters, add 10 dB
For Equivalent values at 30 meters, subtract 10 dB
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