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Relation between # of RF carriers and composite power - RF Cafe
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daverali
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Post subject: Relation between # of RF carriers and composite power
Posted: Tue Apr 10, 2007 11:51 am
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Joined: Sat Sep 18, 2004
7:27 pm Posts: 4 Location: Texas
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Is there a rule of thumb for calculating the composite
power as the number of RF carriers is doubled? I
have heard that it is approximately 2 dB increase
when the # of carriers is doubled. Say, equally
powered carriers at 4 dBm each. When the # of carriers
is 2 is the composite power = 4+2=6 dBm and when
# of carriers is 4, then is the composite power
= 6+2=8 dBm and like that Also, is it protocol
dependent? For example, is the 2 dB rule true for
CDMA carriers only and not the GSM/EDGE based carriers?
The thing is that I can measure this in the field
but I would have to take down a live system just
for the measurements. If someone has already come
across this, that would greatly help. Thanks,
Daver
_________________ Daver Malik RF/Wireless
Engineer
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nubbage |
Post subject:
Posted: Mon Apr 16, 2007 5:19 am
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General |
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Joined: Fri Feb 17, 2006
12:07 pm Posts: 304 Location: London UK
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If the system were to be perfectly linear, then
doubling the number of carriers would add 3dB, so
2 x 4dBm carriers would produce 7dBm total power.
I guess the rule of thumb is warning of 2 mechanisms
in practice that reduce the power: 1) the combining
component will itself add some loss into the system
(say 0.5dB) 2)that due to intermodulation the
power at f1 and at f2 (the frequencies of the two
carriers) is reduced a tad (say another 0.5dB) because
some power from each carrier contributes to the
2*f1+f2, 2*f1-f2, 2*f2+f1 and 2*f2-f1 (among others)
unwanted products of adding the carriers in a non-linear
system.
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Posted 11/12/2012
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