AMERITRON ATR-20 Instruction Manual - Page 2

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ATR-20 Instruction Manual

1.2

Peak Reading SWR/Wattmeter

The ATR-20's cross-needle meter displays peak or average FORWARD power, peak or average

REFLECTED power, and SWR.

The wattmeter can be used without the tuning network by setting the ANTENNA SELECTOR to any of

three COAX DIRECT positions of the antenna selector. The wattmeter is active in all six positions of

the ANTENNA SELECTOR switch.

The ATR-20 must have a power source, or the meter won't function. Power can be provided by an

external 12 Vdc supply (negative ground only) or an internal 9 Volt "transistor radio" battery. The meter

lamp will not illuminate unless an external supply is used.

Battery life is greatly increased through use of an RF controlled solid state battery switch. After a short

period of inactivity, the battery is electronically disconnected.

Full scale forward and reflected power range is controlled by the left METER switch, selecting 3000

watt (HI) or 300 watt (LO). If your transmitter runs more than 300 watts of peak output power, set this

switch to the 3000 watt HI (in) position. If your transmitter has less than 300 watts of peak output, set

this switch to the 300 watt LO switch position (out). Peak envelope power (PEP) is measured by placing

the PEAK or AVG push button (middle METER button) in the PEAK (in) position.

Peak and average power values are equal with steady unmodulated carriers such as closed-key CW,

RTTY, FSK, or FM. The meter reading on these modes will be the same in either peak or average

modes. On SSB, the ratio of PEP to average power varies with different voice and modulation

characteristics. With most voices, the PEP reading is three to five times higher than the average voice

power reading.

Forward power is displayed on the left-hand FORWARD meter scale. This scale is calibrated from 0 to

300 watts and is read directly in the 300 watt LO METER position. Each picket (scale mark) represents

5 watts below 10 watts, 10 watts between 10 and 100 watts, and 25 watts between 100 and 300 watts. In

the 3000 watt (HI) position, multiply the forward power scale 10 times (EXAMPLE: 50 = 500 and 150

=1500 watts).

Reflected power is read on the right-hand REFLECTED meter scale. Full scale reflected power is 60

watts when the meter switch is in the LO position , and 600 watts in the HI position. This scale is

marked with a picket every one watt below 10 watts and every 5 watts above 10 watts. This scale is also

multiplied by 10 when using the HI meter power position.

Power readings are most accurate over the upper half of the meter scales. When measuring power with a

less than perfect match, subtract reflected power from forward power. The result will be the true power.

SWR is read directly from eleven red SWR curves that range from 1:1 to infinity. SWR is measured by

observing the point where forward and reflected meter pointers cross. The SWR is indicated by the red

curve closest to the pointer crossing point. No cumbersome or time consuming SWR sensitivity

adjustments are required with this method.

The power meter and turns counter are backlit with internal lamps. The meter and counter lamps require

power from an external 12 Vdc source. A rear panel jack accepts a 2.1 mm coaxial plug with the center

conductor positive (+) and the outer sleeve negative (-) for powering lamps and metering circuitry. The

negative lead (outer sleeve) is grounded inside the tuner. A meter ON / OFF switch turns the meter and

turns counter lamps off and on, and also turns the meter circuitry off when using battery power.

1.3

Antenna Selector

Ameritron Antenna Tuner