AMERITRON ATR-20 Instruction Manual - Page 4
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ATR-20 Instruction Manual
The roller inductor has maximum inductance when fully counter-clockwise (turns counter 000) and
minimum inductance when fully clockwise (turns counter approximately 124) on the reference counter.
The capacitors have maximum capacitance at 0 and minimum capacitance at 10. In simple language, as
frequency is increased normal control operating positions rotate clockwise.
Note: Always use the most capacitance (capacitor settings closest to 0) allowing a "match". This
insures the tuner is being operated with the highest power handling capacity and least loss
possible. Use the lowest possible inductance (the highest number possible) on the turns counter.
Increasing the capacitor setting numbers and decreasing the INDUCTANCE number (on a given
frequency) INCREASES matching range. This also REDUCES efficiency and power handling
capability of the tuner!
3.1
Initial Antenna Tuning
1. Tune the exciter into a dummy load (most solid state transmitters are "pre-tuned" to 50 ohms and do
not require adjusting with the dummy load).
2. Select the desired antenna with the ANTENNA SELECTOR.
3. Position the ANTENNA,
settings:
Band
ANT/TRANS
160 M:
1
80 M:
1
75 M:
1.5
40 M:
2
30 M:
2.5
4. Place the POWER switch in the LO and AVG meter positions, apply a slight amount of power (25
to 50 watts).
5. Starting from the recommended INDUCTANCE position for the band used, turn the
INDUCTANCE control counter-clockwise (adding more inductance). Tune for lowest reflected
power and maximum forward power (best SWR).
6. In order, adjust the ANTENNA and TRANSMITTER controls for lowest reflected power (best
SWR). Repeat this step a few times until the reflected power is zero or as close to zero as possible.
7. If SWR did not reach 1:1 in step 5, turn the INDUCTOR control counter counter-clockwise (to a
lower number) and repeat Step 5. For maximum power handling and efficiency, always adjust the
capacitors to the lowest front panel number (highest capacitance) that allows proper antenna
matching. This insures maximum power handling and lowest power loss in the tuner.
8. Fully advance the power and, if necessary, touch up the ANTENNA and TRANSMITTER controls
for minimum reflected power and maximum forward power (lowest SWR). Remove the power.
TRANSMITTER, and INDUCTANCE controls at the following
IND
Band
ANT/TRANS
45
20 M:
93
17 M:
98
15 M:
111
12 M:
116
10 M:
4
IND
3
118
3.5
119
4.5
120
5
121
6
121
Ameritron Antenna Tuner