wrote
While measuring the SWR, the needle fluctuates, as the voice is
modulated. Is the "value of SWR" the highest it hits? What's the
convention?
______________

Probably the ratio of forward to reflected power in your antenna system does
not change with the power applied to it. But many tx circuits that measure
SWR must be manually calibrated for the forward power in the system in order
for an ~ accurate indication of SWR.

The best accuracy is possible using CW output, after calibrating the SWR
meter for that forward power level. As the average power during voice
modulation usually is less than the rated average power capability of the
tx, the varying SWR readings you see when voice modulating might all be
lower than the true SWR of the antenna system.

RF