Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

[Phys-L] Re: cable number?

At 07:01 AM 1/31/2005, you wrote:
My colleague has a two-prong BNC cable splitter that reads "3.5 dB" on
each connector. His three prong cable reads 3.5 dB, 7 dB, and 3.5 dB. Are
these signal losses? Anyone familiar with this notation?


When power is specified in terms of dB, it is well to look for the
reference against which this log ratio is being measured.
Sometimes I see XdBmW where the comparison is 1 mW.
Here the reference is to attenuation, where the comparison
is evident: the output power is being measured against the input power -
so we expect a 3.5dB output port to show a little less than half the power
available in the input, and likewise for the other 3.5 dB port

But with this other splitter, you can see that it is not possible for all
three
outputs to deliver the rated fraction of the input power
(about 1/2 plus 1/2 plus 1/4 , i.e. greater than 1!)
- unless the splitter is active. [The other alternative is a choice of using
any two of three output ports...]



Brian Whatcott Altus OK Eureka!