Ramsey Electronics PM10DC, Manual

Page: 32 / 40

PM10DC
y
32
ABOUT VSWR AND TRANSMISSION LOSS
When setting up an antenna, you may think that VSWR match is more critical
than it really is. See the chart to the right to find out how much power is actu-
ally lost due to slight mismatches and how much power is reflected back into
the amplifier where it is lost by heat. It is arguable that a VSWR of 1.38 and
better is more than adequate for transmission powers of up to 500 watts. This
means that at the most you will be getting 2.5% of 500 watts reflected, which
is 12.5 watts. 12.5 watts is really not that much in relation to a high-power am-
plifier, and 12.5 watts lost from power sent over the air will mean nothing to
additional distance coverage. Use caution however, since some transmitters
do not like this much reflected power and instability results, causing spurious
signals and other problems. See your transmitter documentation for more in-
formation on antenna matching.
Note however that most people strive for better than 1.38 simply due to the
fact that they cannot stand the thought of losing even a small percentage of
power due to heat rather than transmission. On very low power transmissions
like micro-power broadcasting, the additional 2.5% of energy not wasted may
bring someone who was in the fringe area into a more acceptable clean trans-
mission range.