Kenwood AT-120 Antenna Tuner

Introduction

The Model AT-120 is a high-performance HF antenna tuner designed to meet your antenna-tuning requirements. It is a modification of the popular AT-200 antenna tuner, offering a compact and lightweight design suitable for both amateur radio shacks and mobile or field operations. The AT-120 integrates an antenna coupler, an SWR meter, and an antenna switch.

This unit has been engineered and manufactured under rigid quality standards to provide satisfactory and dependable operation for many years. Should any trouble arise, please contact your dealer, the nearest KENWOOD service facility, or the factory.

After Unpacking

Save the shipping container and packing materials in case your unit needs to be transported for remote operation, maintenance, or service.

NOTE: If disregarded, inconvenience only. No risk of equipment damage or personal injury.

CAUTION: Equipment damage may occur, but not personal injury.

Features

1. High performance HF antenna tuner, a modification of the popular AT-200.
2. Compact and lightweight, suitable for shack, mobile, or field operation.
3. Consists of an antenna coupler, SWR meter, and antenna switch.
4. Designed for Amateur bands between 3.5 MHz and 30 MHz.
5. Antenna MATCHING or THROUGH operation is selectable via a BAND-switch.
6. SWR meter operates in both THROUGH and MATCHING modes.
7. Includes a mounting bracket for mobile operation.
8. Panel meter can be illuminated by an external power source.
9. The antenna matching circuit is effective in reducing TVI as it acts as a band-pass filter.

Contents

• AT-120 Specifications
• Section 1. Preparation for Use
• Section 2. Controls and their functions
• Section 3. Operation
• Section 4. Circuit Description
• Section 5. Additional Information
• Schematic Diagram

AT-120 Specifications

1. Antenna Coupler

• Frequency range: 5 amateur bands from 3.5 to 29.7 MHz
• Input impedance: 50Ω
• Output impedance: 20 to 300Ω, unbalanced.
• Through power: 150 W max. (3.5 MHz band, 120 W)
• Insertion loss: Less than 0.5 dB at optimum match.

2. SWR Meter

• Frequency range: 3.5 to 29.7 MHz
• Max. power: 150 W
• Measurable range: 1.0:1 to 10:1
• Min. power required: 2 W

3. General

• INPUT Connector: UHF type (50Ω)
• ANT Connector: UHF type (50Ω)
• GND: Wing nut and STUD.
• Dimensions: 152(6")W x 60(2-3/8")H x 159(6-1/4")D mm (inch)
• Weight: 1.6 kg (3.5 lbs) approx.

Section 1. Preparation for Use

Accessories

Carefully unpack your AT-120 Antenna Tuner and verify the following accessories are included:

• Operating manual: 1 copy
• Mounting bracket: 1 piece
• Mounting hardware:
• Screw, 4 mm diameter: 4 pieces
• Flat washer, 4 mm diameter: 4 pieces
• Lock washer, 4 mm diameter: 4 pieces
• Nut, 4 mm diameter: 4 pieces
• Wing Bolt, 4 mm diameter: 4 pieces
• Polyethylene washer: 4 pieces
• 2P power plug: 1 piece
• Ground lug: 1 piece

Interconnection Cable

To connect your AT-120 with the TS-120S(V), or other transceiver, an interconnection cable is required. Refer to Figure 1 for details.

Figure 1. Cable Assembly shows how to prepare the RG-8/U coaxial cable for connection. Ensure the cable is cut evenly, the sheath is scored and removed without cutting the braid, and the braid is trimmed and tinned. Slide the coupling over the cable and carefully solder the connector, avoiding excessive heat that could melt the insulation.

Meter Illumination Power

Power for the meter lamp is supplied from an external power source. Use the supplied 2P (PIN) plug for power-supply connection. Observe polarity. (disregard polarity) Figure 2. Meter Power Connection illustrates the connection.

Section 2. Controls and Their Functions

Front View

Figure 3. Front view displays the front panel controls:

1. Meter: Reads SWR (standing-wave ratio) and is illuminated (external power required).
2. CAL (Calibrate)/SWR Switch: To measure SWR, set this switch to the CAL position. Adjust the CAL control until the meter pointer swings to the CAL line. Then, depress the switch to the SWR position and read the SWR.
3. CAL (Calibrate) Control/Meter Lamp Switch: Used to calibrate the meter. Adjust as described above (item 2). The meter lamp lights when the control is pulled on.
4. BAND Switch: Set this switch to the band in which you are operating. The "THROUGH" position connects the antenna directly to the transceiver, bypassing the coupler, while still allowing SWR measurement. CAUTION: DO NOT operate the band switch while transmitting, as equipment damage WILL occur.
5. R TUNE: Adjusts the resistive component of antenna impedance.
6. X TUNE (Transmit Tuning) Control: Adjusts the reactive component of antenna impedance.

Rear View

Figure 4. Rear View shows the rear panel connections:

1. INPUT Connector: Accepts the HF input signal from the antenna connector on the transceiver.
2. ANT Connector: Accepts the antenna coaxial cable.
3. GND post: Connect the GND post to the transceiver GND stud using the shortest possible cable and the supplied ground lug.
4. 12 VDC: Accepts 12 VDC for meter illumination. Use the supplied plug. NOTE: Viewed from the rear, the right terminal is POSITIVE.
5. Serial No. Plate: Stamped with the unit's Serial Number.

Section 3. Operation

Measuring Antenna System SWR

(i) Using an all solid-state transceiver (such as a TS-120S or TS-120 V)

Before setting up the antenna coupler, determine the antenna system SWR.

1. Set the controls as shown in Figure 5. Connection. Set the BAND switch to the "THROUGH" position.
2. In the transmit mode, calibrate the meter with the calibration control.
3. Depress the CAL/SWR switch to the SWR position and read SWR. If the SWR is lower than 1.5:1, the antenna system impedance is sufficiently matched. If above 1.5:1, tune the system.

NOTE: In the event of too high an SWR (over 10:1), check the antenna system for breaks or a short circuit.

(ii) Using a tube power amplifier transceiver (such as a TS-820)

Connect the transceiver (or transmitter) and dummy load (or antenna) through the AT-120 as shown in Figure 7. Connection. Before setting the antenna coupler, determine the antenna system SWR.

Connect the dummy load to the ANT connector and adjust the (transceiver or transmitter) final tuning. Then, replace the dummy load with the antenna and measure the antenna-system SWR.

NOTE: During antenna measurements, your transceiver may be operating under heavy loading conditions. Your signal may also interfere with other stations. Complete measurements as quickly as possible.

Adjusting the Antenna Coupler

The antenna coupler is used to match a transmitter to an antenna system when its SWR is too high (i.e., greater than 1.5:1 SWR).

1. Place the BAND switch to the same band setting as your transceiver (as shown in Figure 8).
2. Set the CAL/SWR switch to the CAL position.
3. Transmit and adjust the CAL control so the meter indicates CAL.
4. Place the CAL/SWR switch in the SWR position.
5. Adjust the R TUNE and X TUNE controls alternately for a good minimum meter indication. Reflected power will be close to zero as a good match is achieved.

Table 1. shows control positions for coupler adjustment.

Section 4. Circuit Description

Figure 11. Meter Power Connection shows a block diagram of the AT-120.

Directional Coupler

The directional coupler samples forward and reflected power from the transceiver to the load.

Meter Circuit

The forward and reflected power sampled by the directional coupler is used for SWR measurement. Forward power is calibrated with the CAL control so reflected power is read as SWR.

Band Selector Switch

This selects the band to which the matching circuit is tuned. In the "THROUGH" position, the antenna is connected directly to the transceiver, by-passing the coupler, while still allowing SWR measurement.

Antenna Coupler

The universal matching circuit is capable of matching 20 to 300Ω loads to the 50Ω input impedance.

Section 5. Additional Information

1. General Information

The AT-120 has been factory aligned and tested to specifications before shipment. Under normal circumstances, it will operate in accordance with these operating instructions. If your unit fails to work, contact the authorized dealer from which you purchased it for quick, reliable repair. Attempting service without factory authorization can void the unit's warranty.

2. Ordering Spare Parts

When ordering replacement or spare parts for your equipment, be sure to specify the following: Model and serial number of your transceiver, Schematic number of the part, Printed circuit board number on which the part is located, Part number and name, if known, and Quantity desired.

3. Service

Should it become necessary to return the equipment for repair, pack it in its original box and packing, and include a full, detailed description of the problems involved. Also include your telephone number. You need not return accessory items unless they are directly related to the service problem.

NOTE: When claiming warranty service, please include a photocopy of the bill of sale or other proof of purchase showing the date of sale.

Schematic Diagram

The circuit elements may be changed without notice owing to technical innovation.

The schematic diagram for the AT-120 is provided, illustrating the internal components and connections.

Mobile Installation

AT-120 Mobile Installation (Figure 9, 10)

Securely install the Mobile Mount using four lock washers, four flat washers, and four screws and nuts. Install the AT-120 in the Mobile Mount by four wing bolts and polyethylene washers. Adjust the tilt before tightening the bolts.

Figure 9. Mounting bracket shows the mounting bracket assembly with nuts, lock washers, and flat washers.

Figure 10. Adjust the angle illustrates adjusting the tilt using wing bolts and polyethylene washers.