# ARRL

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## dBmV

Oct 10th 2022, 17:08

#### avionicsfun@gmail.com

Joined: Aug 18th 2022, 03:08
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Total Posts: 0
Hello, in prepping for my exam and learning about dB as a ratio of output to the input, it raised a question from earlier in my life when I was a cable television technician. When we would use our field strength meters the set the gain on the amplifiers, we would connect to the amplifier output and measure the gain in dBmV. If db is in fact a ratio, why was just the output used to get the gain dB? Thank you in advance! Mike - KK7IMH
Oct 11th 2022, 12:55

#### avionicsfun@gmail.com

Joined: Aug 18th 2022, 03:08
Total Topics: 0
Total Posts: 0
I think I found the answer to my question. It looks like the output of the amp is compared to the mV rather than the amp input. This is what I found: A 1-mV signal across a pure resistance has a level of 0 dBmV. Signals weaker than 1 mV have negative dBmV values; signals stronger than 1 mV have positive dBmV values, assuming the impedance remains a pure resistance and remains constant.
Jun 29th 2023, 06:38

#### ea7gl

Joined: Dec 4th 2020, 08:51
Total Topics: 0
Total Posts: 0
Or in other words, the reference is an absolute value: 1 mV