SWR
Power Lösses
1:1
=
0
1.3:1
=
2%
1.5:1
=
3%
1.7:1
=
6%
2:1
=
11%
3:1
=
25%
4:1
=
38%
5:1
=
48%
6:1
=
55%
10:1
=
70%
TUNING VOUR ANTENNA
For optimum performance, an SWR meter should be used to tune the antenna. However, since this
meter may cost from §15.00 to §30.00, not everyone may want to invest in its purchase. If possible,
borrow one. If you are unable to borrow one, the RF output meter on your transceiver can be used
as a GUI DE to antenna turning. While it is not 100% accurate, it is generally better than no tuning at
all. Always tune your antenna in an open area. Wires, metal and copper tubing if nearby can effect
the tuning. Never tune an antenna inside a garage, under a metal car port, next to a metal truck, etc.
A.
USING YOUR TRANSCEIVER OUTPUT METER AS A TUNING GUIDE
A fter installing your antenna system, place the whîp halfway into its réceptacle and turn your
transceiver to Channel 20. Depress the switch on your transceiver microphone, and make note
o f the reading on your RF output meter. Loosen the adjustable whip section and move it 1/8 to
1/4 inch down. Again depress the transmit switch, if the reading is the same or lower continue
moving the whip down 1/4 inch at a time until the LOWEST reading is obtained on your
transceiver RF meter. If the reading was higher, move the whip up 1/4 to 1/2 inch the first time
and 1/8 to 1/4 inch thereafter until the LOWEST reading is obtained on the RF meter. That's
rig h t. . . .
THE LOWEST READING. Your RF output meter is a voltage sensing device. It is installed in
the RF output circuit and senses the voltage near the antenna terminal. In a perfectly tuned
system all of the voltage is transferred from the output transistor and passed to the antenna. As
an example, let's use the figure 10. If there is SWR on the line, the forward voltage is 10 and a
reverse voltage appears (let's say it's 2). The meter circuit now sees 20 and shows a higher
reading. You can see that because of the way most RF output meters work, the LOWER your
RF output meter reads the better your antenna is tuned. Of course, if the meter reads less than
1/2 scalę, it may indicate a problem in your set and should be checked. Similarly, an extremely
high reading may indicate a problem in your antenna. An RF output meter can tell you
much . . . especially if you know how to use it.
B.
TUNING YOUR ANTENNA WITH AN SWR METER
Using an SWR meter is the most accurate way to tune an antenna.
Connect the SWR meter as close as possible to the back of the transceiver. Use a double male
connector or a very short piece of RG58/U w ith connectors on each end.
Place the adjustable whip halfway into its réceptacle. Set your transceiver to Channel 20.
Measure the SWR following instructions supplied w ith the meter. A fte r the first measurement,
move the whîp down 1/8 to 1/4 inch and repeat A L L the steps again. If the SWR is lower,
- 13
