Kenwood AT-230

Name: Kenwood AT-230
Brand: Kenwood

Overview

The manual makes a specific claim about the directional coupler. It uses a toroidal coil, which gives flat frequency response across all ranges of operation, so no calibration table is required. No correction charts, in other words. The same toroidal construction shows up in the SWR detection circuit, so both measurement functions follow the same design.

Two controls handle the matching. R TUNE adjusts the resistance component of the antenna, and the CAL control sets the reference for SWR measurement. There is a stud for grounding, and the manual does not soften its advice. Always connect the AT-230 to a good earth ground, using a ground rod and a short run of heavy ground lead or ground braid. Never use house wiring as ground. The manual adds that DC ground is not necessarily RF ground. It calls good grounding essential when running a wire antenna, recommends metal ground rods, and offers a cold water line as a fallback. It also warns that newer water pipes are often polyvinyl rather than metal, and therefore useless for the purpose.

The AT-230 is not consumer hi-fi, and the period audio press treated it that way. Independent coverage of this tuner in the audio magazines is essentially absent. The contemporary coverage that survives from the era is aimed at amplifiers and receivers, not station accessories. For context, Hi-Fi-Stereo-Buyers (May 1979, p.48) covered Hitachi's HA-7700 integrated amplifier, rated at 65 watts per channel RMS with no more than .002% THD. It was the first Hitachi amplifier to use power MOS FET output devices, at a price of about $600. A year earlier, the same publication (May 1978, p.36) reported on Yamaha's CR-420 receiver at 25 watts per channel with less than .05% THD for $280. None of that says anything about the AT-230's performance. The AT-230 sold through amateur radio channels and was reviewed, when it was reviewed at all, by ham publications rather than hi-fi ones.