[Elecraft] OT: math question

AD5MA ad5ma at arrl.net
Wed Mar 30 14:44:20 EST 2005


And while we're on the subject... the correct unit is dB, not dBm.

Remember that dB is a relative term. In the case of amplifier gain, this is
relative. The unit dBm is an absolute unit relative to 1 milliWatt. When the
amplifier is finally built, it will have 50 dBm of output power (assuming it
is driven with enough input signal) and will have 13 dB of gain.

Al.

----- Original Message ----- 
From: "S55M" <s55m at siol.com>
To: <w3fpr at arrl.net>; <Able2fly at aol.com>; <elecraft at mailman.qth.net>
Sent: Wednesday, March 30, 2005 12:41 PM
Subject: Re: [Elecraft] OT: math question


> dBm's
>
> Just remember this (no maths:))) :
> Every 3dB increase is power multiplied by 2 times (1W to 2W is 30dBm to
> 33dBm)
> So 1W+3dB (1x2=2) is 2W+3dB (2x2=4)4W+3dB(4x2=8)8W and so on.
> Every 10dB increase is power multiplied by 10 (1W to 10W is 30dBm to 40dBm
> 100W to 1KW is 50 dBm to 60 dBm the easy one HI)
> And dont care abt digits on calcullator (try to see 0,5dB on Your S-meter
or
> ask someone on the band to change the power from 100W to 50W or from 10W
to
> 5W (3dB) You will see practically no difference.
> Why dBm? Because dBm is power related to 1mW=0dBm .
>
> S55M-Adi
>



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