Kenwood AT-200

A chassisless antenna tuner built to sit between a TS-520 or TS-820 and whatever wire you could string up, with a wattmeter and SWR bridge thrown in.

Overview

The AT-200 is not a hi-fi component, so don't judge it like one. It is an amateur radio antenna tuner. The manual calls it an antenna coupler, and Kenwood built it specifically for use with the TS-520 and TS-820 series transceivers. That one sentence from the operating manual tells you who it was for: the HF operator running a Kenwood rig who needed to match a real-world antenna to a 50-ohm transmitter output without frying the finals.

Kenwood packed a lot into one chassis. The manual describes it as four instruments in one: an antenna coupler, a through-line RF wattmeter, an SWR meter, and an antenna switch. An operator could tune the antenna, watch forward and reflected power on the same meter, verify the match, and switch between antennas without a bench full of separate boxes.

The coupler section covers six amateur bands from 1.8 to 29.7 MHz, with a 50-ohm input impedance and the ability to match antenna impedances from 10 to 500 ohms, unbalanced. Through power is rated at 200 watts maximum, with insertion loss specified at less than 0.5 dB in a well-matched state. On 1.8 MHz only, output impedance runs 20 to 500 ohms with through power limited to 100 watts. These numbers fit the typical 100-watt-class HF transceiver of the era, with headroom at full output on the higher bands and a deliberate derating on top-band.

The wattmeter is a through-line design covering 1.8 to 30 MHz, switchable between 20-watt and 200-watt ranges, and it reads forward or reflected power depending on the switch position. Accuracy is specified at better than ±10% of full scale. That's not lab-grade, but it's honest for a built-in meter, and good enough to tell you whether your match is acceptable before you key down at full power. The SWR meter uses a toroidal-core directional coupler, measures from 1.1 to 10, and needs only 4 watts of drive to give a reading. That low minimum means you can check a match at low power before you push the amplifier.

Kenwood used a toroidal core in the directional coupler to get flat frequency response across all operating bands. The manual points out the practical result: no calibration table is needed.

The antenna switching is more elaborate than the usual A/B arrangement. The AT-200 provides four outputs: two UHF-type connectors for coaxial-fed antennas, one connector for a wire antenna, and one for a dummy load. The rear panel labels these ANT-1, ANT-2, ANT-3, and DUMMY. The manual notes that the dummy load connector is not fed through the antenna coupler. It is a straight connection for aligning or checking the final stage of a transceiver, and Kenwood even included instructions for building a 100-watt dummy load from twenty 1K-ohm, 5-watt metal-film resistors in parallel. The ANT switch also has a THROUGH position, which routes a given antenna directly to the transceiver while still allowing power and SWR measurement.

The wire antenna input is where the AT-200 earns its keep on the low bands. The manual specifically calls out the ability to match a wire antenna such as an inverted-L, which makes the lower frequency bands practical for operators without room for a full-size coax-fed aerial. Kenwood also notes that the matching circuit acts as a band-pass filter, which helps reduce TVI. That was a real concern in the 1970s and early 1980s when this gear was current.

Tuning is done with two controls: R TUNE adjusts the resistance component of the antenna, and X TUNE adjusts the reactance. A BAND switch is set to the appropriate position across the 1.9 to 28 MHz range. The meter circuit is calibrated at the factory, and the manual is blunt about the internal semi-fixed controls VR1 through VR3: they are for precise meter adjustment and should not be touched. If the AT-200 needs service, Kenwood directs owners to an authorized service shop.

One construction detail matters if you buy one today. The AT-200 is chassisless, and the manual explicitly warns against removing the lower case cover. The upper cover comes off with two screws on top and six on the sides, but the bottom stays put. That makes repair awkward. Kenwood also supplied extension feet that raise the front of the unit by around 15 mm, tilting the panel forward for easier reading.

Physically, the AT-200 measures 166 mm wide, 153 mm high, and 190 mm deep, and weighs approximately 2.8 kg (6.2 lbs). The connectors are UHF type for the 50-ohm input and for ANT-1 and ANT-2. ANT-3 is wire-only, and there is a ground post that the manual says should be connected with as short a wire as possible whenever a wire antenna is used.

The AT-200 is a period accessory rather than a standalone component, and it was sold as such. It was a practical tool from a company that was, by its own advertising, positioning itself as "the pacesetter in amateur radio." As the audio press of the period noted in its coverage of Kenwood's product lineup, the company's amateur line was showcased alongside its consumer audio range at trade events such as the Consumer Electronics Show, where new models for the coming year were introduced to dealers and sales representatives (Audio August 1973, p.24).

For collectors today, the AT-200 is not a rare piece, and it is not a high-value one. It is useful. An operator running a TS-520 or TS-820, or any 100-watt HF rig with a 50-ohm output, can put an AT-200 in line and get tuning, metering, and antenna switching in a single box that takes up less shelf space than the separates it replaces. The 200-watt through-power rating gives it enough margin for most vintage HF transceivers, and the 4-watt minimum for SWR measurement means it can be used carefully at low power.

The caveats are the usual ones for gear of this age. The chassisless construction makes internal service more awkward than it should be, and the factory-set meter calibration controls are best left alone unless the meter is demonstrably off. The UHF connectors are period-correct but not what a modern operator would choose. And the 1.8 MHz derating to 100 watts is a real limitation for anyone running full power on top band.

None of that changes what the AT-200 is: a well-considered, honest accessory from the era when Kenwood's amateur line was at its most confident. It does exactly what it says on the front panel, and it does it without asking for much in return.