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roustabout
Joined: 30 Jun 2004
Posts: 52
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 14 Oct 2004 2:29 dBm...which is larger? |
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Assume that mobile
receivers require minimum of 100dBm received power to operate. Plot the
corresponding attachment map. Plot the received power of the contour points
based on the larger values of the signal power from both transmitters.
Am i correct....i have to find values which are less than or equal - 100 dBM. So the values that i have to look for are - 101 , - 103
Please help me clear this up. I'm confused
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IanP
Joined: 05 Oct 2004
Posts: 6346
Helped: 1505
Location: West Coast
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| 14 Oct 2004 2:57 Re: dBm...which is larger? |
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Please remember that dBm is not a value of a signal but it is ratio between power of two signals: reference (0dBm) and this one that you measure. So -101dBm indicates that the power of a signal is lower than that of -100dBm. If you go to the oter side of 0dBm the story is opposite: 1dBm indicates more power then 0dBm.
I hope this is of any help to you... 
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roustabout
Joined: 30 Jun 2004
Posts: 52
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| 14 Oct 2004 3:36 Re: dBm...which is larger? |
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refering to the first post....
the mobile needs min signal of - 100 dBm. larger value of the signal means that ... one have look for signal >= - 100 dbm in order to operate...
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djalli
Joined: 10 Nov 2001
Posts: 887
Helped: 15
Location: 1600 Pennsylvania Avenue, Washington DC 20500
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| 14 Oct 2004 6:25 dBm...which is larger? |
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100dBm=1E10 mili watts or 10000 kiloWatts
101dBm=1.2589E10 mili watts or 12589 kWatts
-100dBm=1E-10 mili watts or 0.1 picoWatts
-101dBm=1.2589E-10 mili watts or 0.12589 picoWatts
is this correct?
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echo47
Joined: 07 Apr 2002
Posts: 4205
Helped: 565
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| 14 Oct 2004 6:54 dBm...which is larger? |
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IanP, you are thinking of dB. dBm is an absolute power measurement, "decibels relative to a milliwatt".
Yes djalli. The handy equation is: dBm = 10 * log(watts / 0.001)
Guys, be careful with plus and minus signs, and 'm' and 'M'. 
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amraldo
Joined: 29 Aug 2004
Posts: 255
Helped: 23
Location: egypt, cairo
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| 14 Oct 2004 10:25 Re: dBm...which is larger? |
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| larger values in dbm are -90 dbm,...., 0dbm, 110dbm,.....
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devrimaksin
Joined: 13 Oct 2004
Posts: 93
Helped: 9
Location: Dallas, Texas, USA
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| 15 Oct 2004 2:37 Re: dBm...which is larger? |
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| dBm is an absolute power value refered to 1mW
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djalli
Joined: 10 Nov 2001
Posts: 887
Helped: 15
Location: 1600 Pennsylvania Avenue, Washington DC 20500
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| 15 Oct 2004 6:55 dBm...which is larger? |
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Engineers do it because in decibels multiplication is addition and division is substraction.
To be honest they call engineers lazy because of that, I heard it a lot. Do you think this is right?
here is beauty of decibels:
21mW/0.25mW = 84mW *
in dBM
21mW=13.222dBm
0.25mW=-6.0206dBm
so 13.222dBm-(-6.0206dBm)=19.25dBm /*just substraction*/
10^(19.25/10)=83.99 * same!
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pico
Joined: 30 Sep 2001
Posts: 261
Helped: 6
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| 15 Oct 2004 8:09 dBm...which is larger? |
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roustabout;
The value that you have to look for should be -99, -98,... -90dBm which are more than -100dBm, remember it's in minus sign (-).
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