db is a generic term basically meaning: Decibel. A unit for measuring the
relative strength of a signal. Usually expressed as the logarithmic ratio of
the strength of a transmitted signal to the strength of the original signal.
A decibel is one tenth of a "bel".

the key is that it is a ratio... without a reference a ratio is essentially
meaningless. that is why you often hear that station a is 10db louder than
station b... saying that station a was 10db wouldn't mean anything.

dbm has a built in reference. by definition: Decibels referred to 1
milliwatt.
so the reference is 1 mw. do you can say that the power of a source is 0dbm
meaning that it is 1mw, 10dbm is 10mw, 20dbm is 100mw, -10dbm is .1mw, -20db
is .01mw, etc.

i don't know an ip3, but maybe that will give you a start to know what you
are looking for.



"jason" wrote in message
ups.com...
Hello All

I am beginner in RF
I may ask about some silly question and please pardon me
May I know what actually the unit of dbm and db is different from one
another?
If they are different how can we minus the gain in unit of db from a
IP3 in unit of dbm?
Kindly enlighthen
Thank you all


rgds and thanks
Jason

dB is a ratio for example dB = 10 log10 (P1/P2)
so increasing power from 100 watts to 200 watts is 3 dB (3.01dB actually)
But so is increasing power from 10 watts to 20 watts = 3dB
Since it is a ratio -- it is unitless

dBm is referenced to one milliwatt thus is a discrete power level

In the equation above P2 is always one milliwatt

Thus increasing power from 1 milliwatt to 2 milliwatts is 3dBm
From 1 milliwatt to 10 milliwatts is 10dBm etc

Not sure of your reference to ip3 but suspect you mean input third order
intercept point as used in amplifiers
Google ip3 to get explanations of this and how it is measured.
--
Caveat Lector (Reader Beware)


"jason" wrote in message
ups.com...
Hello All

I am beginner in RF
I may ask about some silly question and please pardon me
May I know what actually the unit of dbm and db is different from one
another?
If they are different how can we minus the gain in unit of db from a
IP3 in unit of dbm?
Kindly enlighthen
Thank you all


rgds and thanks
Jason

"Caveat Lector" wrote
dB is a ratio for example dB = 10 log10 (P1/P2)
....snip...
In the equation above P2 is always one milliwatt
___________________

To elaborate, P2 above must be 1 mW only if one wants to calculate dBm.

The equation as it is written above will calculate the relationship in
decibels between any two power values expressed in the same units. For
example, to find the gain of an amplifier in decibels when its input power
is 50 watts and its output power is 1.2 kW:

dB = 10*log(1200/50) = 10*log(24) = 10*1.38 = 13.8

RF

Thanks for the clarification

I meant to say "For dbm In the equation above P2 is always one milliwatt"

Thanks

--
Caveat Lector (Reader Beware)



"Richard Fry" wrote in message
...
"Caveat Lector" wrote
dB is a ratio for example dB = 10 log10 (P1/P2)
...snip...
In the equation above P2 is always one milliwatt
___________________

To elaborate, P2 above must be 1 mW only if one wants to calculate dBm.

The equation as it is written above will calculate the relationship in
decibels between any two power values expressed in the same units. For
example, to find the gain of an amplifier in decibels when its input power
is 50 watts and its output power is 1.2 kW:

dB = 10*log(1200/50) = 10*log(24) = 10*1.38 = 13.8

RF