Radio Receiver Design
This reference focuses on understanding and designing radio receivers and systems, presenting the characteristics of individual receiver components and their interaction in cascade.
TABLE OF CONTENTS Radio Receiver Design
1.5: Signal Standards
1.5 Signal Standards
The decibel format is commonly used to express absolute power or voltage levels. To do this, we replace P 1 in Equation 1.3 with a standard value. For example, if we are dealing with a system where milliwatt power levels are common, we might choose P 1 to be 1 mW and Equation 1.3 would become
| (1.11) |  |
where
P Measured,mW = the power level measured in mW,
P Measured,W = the same power level measured in watts.
Note that Equation 1.11 defines the dBm standard.
dBm
dBm is the oldest standard way of expressing measurements. It was originally devised by a telephone company to measure signal levels on their lines and has been widely adapted. The reference power for dBm is 1 milliwatt. (The m in dBm stands for power referenced to 1 mW) A quantity expressed in dBm represents an absolute power level, for example, P out = 20 dBm.
| (1.12) |  |
| (1.13) |  |
The impedance of a telephone line is about 600 ohms; hence 1mW (or 0 dBm) measures a little less than 0.775 V RMS. In a 50-ohm system, a 1 mW or 0 dBm sine wave has a RMS voltage of 0.224 V RMS.
dBW
dBW is a power measurement referenced to 1 watt. dBW is an absolute unit for expressing power level and is widely used in the world of transmitting equipment.
| (1.14) |  |
| (1.15) |  |
Example 1.2: dBm and dBW
Find an expression relating dBm and...
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