I began looking through the presentation on the nano,
and immediately caught an error in the table comparing
"ham conventions" versus "More modern conventions".
For "no reflections" the correct return loss expressed in dB
is a positive infinite value, not negative as shown in the table.
More pragmatically, the return loss of any passive device is
a positive number of dB. For example, a "pretty good termination"
might show a return loss of +32 dB.
I know that many people get this wrong. But if you pay attention
to the meaning of the word 'loss', then a negative value in dB
really means a gain (reflected signal more powerful than the
incident signal), which really is possible for active devices like
amplifiers etc.
I once gave a demo of a home brew Time Domain Reflectometer
(TDR) at a club meeting, and finished up with a DUT which I had
lovingly crafted with a tunnel diode to produce return gain over
a wide band. I showed this, pointing out that the reflected signal
was larger than the incident, then challenged the audience to
say what was in the box. Only one guy got it right.
Dana (K8YUM)
