|
CATV dBm, dBmV, and dBµV
Conversions
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the MAX3507
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Sheet for the MAX3509
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MAX3514/MAX3516/MAX3517
Additional
Information: Applications Technical Support
Introduction
CATV circuits operate in a 75 environment. Most RF
laboratories equipped with standard test instruments employ 50 as the standard
interface impedance.
dBmV and dBµV
Most CATV measurements are referenced to voltage and measured in dBmV
or dBµV. In the classic definition, dBmV is referenced to 1mVrms and
output voltage (Vout) is measured in mVrms (EQN1). Since EQN1 is a ratio
of voltage, it can also be measured in mVpp referenced to 1mVpp or any
voltage unit as long as the same units are used.
Inspection of EQN1 shows dBmV to be independent of impedance.
In the classic definition, dBµV is referenced to 1µVrms and output
voltage (Vout) is measured in µVrms (EQN2). Since EQN1 is a ratio of
voltage, it can also be measured in µVpp referenced to 1µVpp or any
voltage unit as long as the same units are used.
Inspection of EQN1shows dBµV to be independent of impedance.
Conversion
of dBm to dBmV
dBm is defined in EQN3.
Pout is measured in mW. The dBm is referenced to 1mW. EQN3 does depend
on impedance of the load as shown in EQN4. Most RF equipment has a 50 load or input
impedance. EQN3 is still valid for any load impedance including 75.
Power depends on load impedance. EQN4 equates power to voltage and load
impedance.
Rearranging terms,
Solving EQN3 for Pout,
Solving EQN1 for Vout,
Substituting EQN3.1 and EQN1.1 into EQN4.1,
Solving for dBmV in terms of dBm,
Using R = 50,
EQN5.2 is valid for 50 measurement equipment.
Solving EQN5.1 using R = 75,
EQN5.3 is valid for 75 measurement equipment.
Using the same technique it can be shown that the relationship for dBµV
to dBmV is
Table 1 and Table 2 show conversions between dBmV, dBµV and dBm in a
50 and 75 environment.
Table 1. Conversions of
Power 50 Ohms
|
dBmV |
dBµV |
dBm 50 |
mVrms |
mW 50 |
|
8 |
68 |
-38.99 |
2.51 |
1.3E-04 |
|
9 |
69 |
-37.99 |
2.82 |
1.6E-04 |
|
10 |
70 |
-36.99 |
3.16 |
2.0E-04 |
|
11 |
71 |
-35.99 |
3.55 |
2.5E-04 |
|
12 |
72 |
-34.99 |
3.98 |
3.2E-04 |
|
13 |
73 |
-33.99 |
4.47 |
4.0E-04 |
|
14 |
74 |
-32.99 |
5.01 |
5.0E-04 |
|
15 |
75 |
-31.99 |
5.62 |
6.3E-04 |
|
16 |
76 |
-30.99 |
6.31 |
8.0E-04 |
|
17 |
77 |
-29.99 |
7.08 |
1.0E-03 |
|
18 |
78 |
-28.99 |
7.94 |
1.3E-03 |
|
19 |
79 |
-27.99 |
8.91 |
1.6E-03 |
|
20 |
80 |
-26.99 |
10.00 |
2.0E-03 |
|
21 |
81 |
-25.99 |
11.22 |
2.5E-03 |
|
22 |
82 |
-24.99 |
12.59 |
3.2E-03 |
|
23 |
83 |
-23.99 |
14.13 |
4.0E-03 |
|
24 |
84 |
-22.99 |
15.85 |
5.0E-03 |
|
25 |
85 |
-21.99 |
17.78 |
6.3E-03 |
|
26 |
86 |
-20.99 |
19.95 |
8.0E-03 |
|
27 |
87 |
-19.99 |
22.39 |
0.010 |
|
28 |
88 |
-18.99 |
25.12 |
0.013 |
|
29 |
89 |
-17.99 |
28.18 |
0.016 |
|
30 |
90 |
-16.99 |
31.62 |
0.020 |
|
31 |
91 |
-15.99 |
35.48 |
0.025 |
|
32 |
92 |
-14.99 |
39.81 |
0.032 |
|
33 |
93 |
-13.99 |
44.67 |
0.040 |
|
34 |
94 |
-12.99 |
50.12 |
0.050 |
|
35 |
95 |
-11.99 |
56.23 |
0.063 |
|
36 |
96 |
-10.99 |
63.10 |
0.080 |
|
37 |
97 |
-9.99 |
70.79 |
0.100 |
|
38 |
98 |
-8.99 |
79.43 |
0.126 |
|
39 |
99 |
-7.99 |
89.13 |
0.159 |
|
40 |
100 |
-6.99 |
100.00 |
0.200 |
|
41 |
101 |
-5.99 |
112.20 |
0.252 |
|
42 |
102 |
-4.99 |
125.89 |
0.317 |
|
43 |
103 |
-3.99 |
141.25 |
0.399 |
|
44 |
104 |
-2.99 |
158.49 |
0.502 |
|
45 |
105 |
-1.99 |
177.83 |
0.632 |
|
46 |
106 |
-0.99 |
199.53 |
0.796 |
|
47 |
107 |
0.01 |
223.87 |
1.002 |
|
48 |
108 |
1.01 |
251.19 |
1.262 |
|
49 |
109 |
2.01 |
281.84 |
1.589 |
|
50 |
110 |
3.01 |
316.23 |
2.000 |
|
51 |
111 |
4.01 |
354.81 |
2.518 |
|
52 |
112 |
5.01 |
398.11 |
3.170 |
|
53 |
113 |
6.01 |
446.68 |
3.991 |
|
54 |
114 |
7.01 |
501.19 |
5.024 |
|
55 |
115 |
8.01 |
562.34 |
6.325 |
|
56 |
116 |
9.01 |
630.96 |
7.962 |
|
57 |
117 |
10.01 |
707.95 |
10.024 |
|
58 |
118 |
11.01 |
794.33 |
12.619 |
|
59 |
119 |
12.01 |
891.25 |
15.887 |
|
60 |
120 |
13.01 |
1000.00 |
20.000 |
|
61 |
121 |
14.01 |
1122.02 |
25.179 |
|
62 |
122 |
15.01 |
1258.93 |
31.698 |
|
63 |
123 |
16.01 |
1412.54 |
39.905 |
|
64 |
124 |
17.01 |
1584.89 |
50.238 |
|
65 |
125 |
18.01 |
1778.28 |
63.246 |
|
66 |
126 |
19.01 |
1995.26 |
79.621 |
|
67 |
127 |
20.01 |
2238.72 |
100.237 |
|
68 |
128 |
21.01 |
2511.89 |
126.191 |
Table 2. Conversions of
Power 75 Ohms
|
dBmV |
dBµV |
dBm 75 |
mVrms |
mW 75 |
|
8 |
68 |
-40.75 |
2.51 |
8.4E-05 |
|
9 |
69 |
-39.75 |
2.82 |
1.1E-04 |
|
10 |
70 |
-38.75 |
3.16 |
1.3E-04 |
|
11 |
71 |
-37.75 |
3.55 |
1.7E-04 |
|
12 |
72 |
-36.75 |
3.98 |
2.1E-04 |
|
13 |
73 |
-35.75 |
4.47 |
2.7E-04 |
|
14 |
74 |
-34.75 |
5.01 |
3.3E-04 |
|
15 |
75 |
-33.75 |
5.62 |
4.2E-04 |
|
16 |
76 |
-32.75 |
6.31 |
5.3E-04 |
|
17 |
77 |
-31.75 |
7.08 |
6.7E-04 |
|
18 |
78 |
-30.75 |
7.94 |
8.4E-04 |
|
19 |
79 |
-29.75 |
8.91 |
1.1E-03 |
|
20 |
80 |
-28.75 |
10.00 |
1.3E-03 |
|
21 |
81 |
-27.75 |
11.22 |
1.7E-03 |
|
22 |
82 |
-26.75 |
12.59 |
2.1E-03 |
|
23 |
83 |
-25.75 |
14.13 |
2.7E-03 |
|
24 |
84 |
-24.75 |
15.85 |
3.3E-03 |
|
25 |
85 |
-23.75 |
17.78 |
4.2E-03 |
|
26 |
86 |
-22.75 |
19.95 |
5.3E-03 |
|
27 |
87 |
-21.75 |
22.39 |
6.7E-03 |
|
28 |
88 |
-20.75 |
25.12 |
8.4E-03 |
|
29 |
89 |
-19.75 |
28.18 |
0.011 |
|
30 |
90 |
-18.75 |
31.62 |
0.013 |
|
31 |
91 |
-17.75 |
35.48 |
0.017 |
|
32 |
92 |
-16.75 |
39.81 |
0.021 |
|
33 |
93 |
-15.75 |
44.67 |
0.027 |
|
34 |
94 |
-14.75 |
50.12 |
0.033 |
|
35 |
95 |
-13.75 |
56.23 |
0.042 |
|
36 |
96 |
-12.75 |
63.10 |
0.053 |
|
37 |
97 |
-11.75 |
70.79 |
0.067 |
|
38 |
98 |
-10.75 |
79.43 |
0.084 |
|
39 |
99 |
-9.75 |
89.13 |
0.106 |
|
40 |
100 |
-8.75 |
100.00 |
0.133 |
|
41 |
101 |
-7.75 |
112.20 |
0.168 |
|
42 |
102 |
-6.75 |
125.89 |
0.211 |
|
43 |
103 |
-5.75 |
141.25 |
0.266 |
|
44 |
104 |
-4.75 |
158.49 |
0.335 |
|
45 |
105 |
-3.75 |
177.83 |
0.422 |
|
46 |
106 |
-2.75 |
199.53 |
0.531 |
|
47 |
107 |
-1.75 |
223.87 |
0.668 |
|
48 |
108 |
-0.75 |
251.19 |
0.841 |
|
49 |
109 |
0.25 |
281.84 |
1.059 |
|
50 |
110 |
1.25 |
316.23 |
1.333 |
|
51 |
111 |
2.25 |
354.81 |
1.679 |
|
52 |
112 |
3.25 |
398.11 |
2.113 |
|
53 |
113 |
4.25 |
446.68 |
2.660 |
|
54 |
114 |
5.25 |
501.19 |
3.349 |
|
55 |
115 |
6.25 |
562.34 |
4.216 |
|
56 |
116 |
7.25 |
630.96 |
5.308 |
|
57 |
117 |
8.25 |
707.95 |
6.683 |
|
58 |
118 |
9.25 |
794.33 |
8.413 |
|
59 |
119 |
10.25 |
891.25 |
10.591 |
|
60 |
120 |
11.25 |
1000.00 |
13.333 |
|
61 |
121 |
12.25 |
1122.02 |
16.786 |
|
62 |
122 |
13.25 |
1258.93 |
21.132 |
|
63 |
123 |
14.25 |
1412.54 |
26.604 |
|
64 |
124 |
15.25 |
1584.89 |
33.492 |
|
65 |
125 |
16.25 |
1778.28 |
42.164 |
|
66 |
126 |
17.25 |
1995.26 |
53.081 |
|
67 |
127 |
18.25 |
2238.72 |
66.825 |
|
68 |
128 |
19.25 |
2511.89 |
84.128 |
September 2001 | 
