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HOW TO TUNE AN ANTENNA
An efficient antenna is a well matched antenna! The PM10DC allows you to
easily match your antenna to your transmitter. Connect the PM10DC between
your transmitter and antenna and set the display to the VSWR mode. You will
see VSWR indicated which is indicative of the quality of the antenna match.
The lower the value, the better the match.
Make note of your current VSWR reading.
If you are using a vertical antenna, add a short length of wire (about an inch
or so) to the tip of the antenna, making it slightly longer. Or if you have a pro-
fessional antenna, telescope the antenna about an inch longer. Did the VSWR
reading go up or down? If the value went down, you are getting closer to a
good match, and the antenna should be longer than it currently is. If the value
went up, the antenna needs to be shorter.
If the value went up, remove the added wire, and see if the VSWR goes
back down. Now this tells you that you are heading in the right direction and
you should start "trimming" your antenna. Be careful though, don't start cutting
long pieces off the antenna; stick with a quarter of an inch at a time. When the
VSWR reading starts to go back up or levels out, stop trimming!
If the value went down, you will have to find a permanent way of appending
a length of durable wire to the end of your antenna. This will depend entirely
on your antenna, but the benefits of a good match are so positive it is worth
the trouble!
Other antennas are tuned in the same manner. We simply adjust antenna
length for minimum VSWR.
How low is low enough? In most cases anything better than 1.5 is consid-
ered good. When we start talking power in the hundreds of watts, then we
would like to see a better match. This is generally due to the reflected power
leading to heating troubles within the amplifier itself. Instead of the power be-
ing transmitted away over the air it now needs to be dissipated inside of the
transmitter. Changing VSWR readings below 1.5 typically don't effect trans-
mission range.
See VSWR and Transmission loss on the next page.
PM10DC 31
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