**EMRFD Message Archive 3088**

MessageDateFromSubject3088 2009-05-23 07:37:47 Kenneth Stringham Power Ratios Well, I was taught that dBm dBmW is the power ratio in deci-Bels relative 1mW in the standard system. This implies 50 ohms for RF and 600 ohms for audio. It would seem to me that one could extend this to a 75 ohms system when dealing with CCTV or CATV applications.

Voltage ratio is not necessarily based on power. An ideal amplifier has a infinite input impedance and a zero output impedance, yet this ideal model has a voltage gain that may be expressed in dB or dBv, dBmV, or any other standard type ratio. The ideal amplifier would have infinite power gain this case. A real amplifier approaches this as close as is practical, but the fact remains the same that the power gain is not equal to the voltage gain, but the voltage gain can still be expressed in dB.

Ken - AE1X3094 2009-05-23 09:07:44 jocjo_john Re: Power Ratios