Yes, SWR is a dimensionless quantity. dB is, as far as I know, defined
only for power, voltage and current ratios, as the IEEE Dictionary
implies. Since it's defined differently for power than for voltage or
current (so that an increase or reduction in one quantity represents the
same number of dB increase or decrease in the other), anyone using it
for something else would have to clarify how it would be defined in that
context.

Roy Lewallen, W7EL

Cecil Moore wrote:
H. Adam Stevens, NQ5H wrote:

"Cecil Moore" wrote:
The log of the ratio of two SWRs doesn't seem to have much
meaning.

It's called db, Cecil.


The IEEE Dictionary says the ratio of power, voltage, and
current can be expressed in dB. It specifically states
that dB can only be related to power ratios or to parameters
that are proportional to the square root of power ratios.

SWR1 = [SQRT(Pfor1)+SQRT(Pref1)]/[SQRT(Pfor1)-SQRT(Pref1)]

SWR2 = [SQRT(Pfor2)+SQRT(Pref2)]/[SQRT(Pfor2)-SQRT(Pref2)]

The ratio of two SWRs will not reduce to a power ratio or
to the square root of a power ratio.