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."

.




--
Ian