On Thu, 2 Sep 1999, james nolan wrote:
> The SWR meter that checks the boat radio, cable and antenna measures the
> standing wave ratio of the radio signal on the cable. The SWR is the ratio
> of the maximum voltage to the minimum voltage of the standing voltage wave
> on the cable. A high SWR causes the transmitter to heat up and decreases the
> transmitted signal power. The maximum and minimum voltages occur at two
> different places on the cable (related by the wavelength of the signal) and
> yet the SWR meter needs only to be inserted in one place and that place
> along the cable is not particular. How does the SWR meter know the peak and
> minimum voltages on the cable since it may not be installed at either the
> location of a peak or minimum?
>
> Jim Nolan P-19, P-15, L138T, LGYC #6
Actually the SWR can be measured either by voltage (vswr) or current.
Another way to measure it is by measuring the amount of power that is
going forward (toward the ant.) and comparing it to the amount of power
that is being reflected back toward the transmitter. That kind of
measurment can be made at any point along the feedline and give a good
indication of the vswr along the feedline. This is the usual method used
with cheap, convienent equipment. Just remember one thing...if your
feedline has infinite loss, the swr reading at the transmitter will say
1:1 (whatever power forward and 0 power reflected because of the feed line
loss) but you won't be putting out much of a signal!
Why do I somehow think that you know these things....are you asking them
specifically to help the rest of us think about them?????
Rich Gort W7JVL
WWP19 #202 SAYOKO
Lake Stevens, WA