[Amps] coaxial stub on amplifier output

Bill, W6WRT dezrat1242 at yahoo.com
Sat Apr 3 14:56:23 PDT 2010


ORIGINAL MESSAGE:

On Sat, 3 Apr 2010 09:48:29 -0700, James Colville <jimw7ry at gmail.com>
wrote:

>Get your calculator out.  30dB down from 1500 watts is how much power?
>
>
>1500 watts=+61.8 dBm minus 30 db (which is what the harmonic would be down
>normally) =  +30dBm.  +30dBm = 1 watt. Evenif the harmonic is only down 25
>db, that is only 3 watts.

REPLY:

Don't need a calculator. Each -10 dB = 10x power reduction.

10 dB down from 1500 watts is 150 watts.
10 dB down from 150 watts is 15 watts.
10 dB down from 15 watts is 1.5 watts.

Ergo, 30 dB down from 1500 watts = 1.5 watts.

An even quicker way if you have a calculator that does exponents:
Convert dB to B (i.e. divide by 10) then figure 10 to the B power,
which becomes the power reduction factor, in this case 1000, and
divide the original power by 1000. Answer = 1.5 watts.

This example is for power reduction but the same principle applies to
power increases. Just multiply instead of divide.

73, Bill W6WRT




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