On 9/29/2015 4:36 AM, Jeff wrote:
On 29/09/2015 00:57, Jerry Stuckle wrote:
On 9/28/2015 6:18 PM, Ian Jackson wrote:
In message , Roger Hayter
writes



It would probably make more sense to call return loss "return gain",
but, since it is always less than one, that would merely cause a
different set of ambiguities.

The reflected signal is an attenuated version of the forward (source)
signal. It is a 'loss' - in exactly the same way as the signal at the
output end of an attenuator is an attenuated version of the source
signal at the input end. The RLR (in dB) is the ratio of the what you
put in to what you get out. It cannot be less than 1, so the RLR is in
positive dB. There is absolutely no ambiguity. No one in RF engineering
quotes or uses negative values for RLR (or for attenuators). The greater
the RLR, the less signal is reflected.




The ratio of output to input can never be greater than one - so the log
of that can never be positive.

I.E. 100W in and 50W out is -3db, not +3db.


Yes, that is a GAIN of -3db. When considering RL you are looking for a
reduction (LOSS) in the reflected power so the sign changes.

It is just common sense.

Jeff

OK, so I have a system with gains and losses of +3, +1, +5, +2. What it
the total gain of the system?

In college we learned to consider everything a "black box". You don't
know whether it is active or passive, an amplifier or an attenuator.
All you know are the characteristics. If the output has +db over the
input, it is an amplifier. -db indicates a loss.

The same is true when modeling antennas. The antenna connection is a
black box. Returned power is always less than power going into it.

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