2 clarify the mystery (again
)
dBm is 1 milliwatt (NOT millivolt) reference.
Its used when POWER levels r compared, not VOLTAGE.
When fixed VOLTAGE (absolute value) is discussed in reference 2 POWER, impedance HAS GOT to b mentioned.
BECAUSE: as we all know POWER= VOLTAGE 2 (square) / impedance.
In a known application such as pro-audio, transmission etc. , impedance is assumed 2 b known, thus omitted.
SO: When U were measuring an RF transmission device, the unit was 0 dBm = 1 milliwatt (WATT, WATT
) across a 50 Ohm load, which is a known transmission standard.
In other words U were measuring 0dBm(50).
The VOLTAGE U were measuring was : V= root of ( P x R)= root of (0.001 x 50) = 0.2236067 Volts.
So
0dBm(50) > 0.2236067 Volt
If U were measuring a TV system the standard would have been 75 Ohms.
If U were measuring a PRO-AUDIO system the standard would have been 600 Ohms.
When the application / impedance is not clearly stated, dBm is written WITH the impedance value as in:
קוד: |
dBm(600) 0dBm(600)> 0.7745966 V = ~0.775V
dBm(75) 0dBm(75)> 0.2738612 V = ~0.274V
dBm(50) 0dBm(50)> 0.2236067 V = ~0.224V
|
dBmW is the generic form when no application is mentioned, thus no VOLTAGE is referenced.
BTW: There is a unit defined as dBW, for the transmission standard. However, it is referenced to 1Watt = 1000 milliwatt.
0 dBW =1 watt measured with respect to 50 ohms.
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Sorry 4 all the numbers flying around, they may disturb a tender soul or 2.
But this is YODA talking NOT ME!!! The little green MF pops out of his swamp every now & then
From now on Ill keep my moth shut and go back 2 being the COOL blonde Jedi knight that I m
Like, 0dBm?
DUH?
There. I feel much better now
Peace,
Zooot.