"Ian Jackson" wrote in message ...

In message , John S
writes
On 9/29/2015 1:45 PM, Wayne wrote:



We always used positive numbers and viewed RL as the difference in dB
between the forward and reflected power.

That makes perfect sense. You could never have a negative dB.

It might be instructive for us all to have a quick look at this information
(especially the last sentence!):

http://www.microwaves101.com/encyclopedias/vswr

"Thus in its correct form, return loss will usually be a positive number.
If it's not, you can usually blame measurement error. The exception to the
rule is something with negative resistance, which implies that it is an
active device (external DC power is converted to RF) and it is potentially
unstable (it could oscillate). Not something you have to worry about if you
are just looking at coax cables! However, many engineers often omit the
minus sign and talk about "-9.5 dB return loss" for example. People that
find it necessary to correct engineers who do this have underwear that is
too tight."

LOL. Yes I have run into people like that.

Years ago, I worked with a young engineer who would ask me the following
question when I said "SWR".
He would ask "Do you mean VSWR?"

After a few of his questions, I constructed a nomograph that would convert
SWR to VSWR for him.
And I even wrote an equation for him. SWR=10(VSWR)/10

hope this doesn't start a new thread