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Garmin GDS 20 Sounder Module

This sounder module is a well-designed accessory.

October 4, 2007
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Garmin’s top-end color chart plotters—the GPSMap 2006C and 2010C—have been widely acclaimed for their crisp displays, user-friendly control logic and value pricing. The development of the GDS 20 sounder module, a remote-mounted accessory for these units, greatly enhances their utility.

The sounder module was introduced in mid-2002, and deliveries began in late fall. Yachting tested the GDS 20 sounder with a GPSMap 2010C display mounted on a Packet Craft 360 Express Cruiser. The bright, colorful sonar display pages integrated perfectly with the chart plotter’s traditional navigation pages, and the soft-key labeling and logic was flawless. The presentation was so well mapped that our first-time users powered up the control display unit, and found and used the sonar pages, without consulting the owner’s manual.

Garmin’s GDS 20 sounder transceiver and processor are housed in a waterproof aluminum alloy case that measures 63/4 inches long by 43/4 inches wide by 2 inches high. It’s designed to be mounted in an out-of-the-way location-typically behind the instrument panel or inside a center console. The 30-foot data cable provided with the unit allows plenty of installation flexibility.

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The sounder module runs on 10 to 35VDC, draws a maximum of 18 watts, and is fused at 2.0 amps. It generates 50 and 200 kHz pulses at 500 watts RMS (4,000 watts peak). That power and frequency combination can read bottoms as deep as 1,500 feet, depending on salinity, temperature and type of bottom. Two LEDs on the case provide diagnostic blink codes for troubleshooting. The circuitry in the GDS 20 will be used as a kernel in a future line of Garmin sounders.

You can select a transducer from a wide assortment of Garmin devices and others offered by after-market vendors. Transducers work like underwater speaker/microphones propagating “pings from the boat to the bottom, and listening for echo returns. (See “The Voice and Ears, January, for more on selecting transducers.) The GDS 20 processes information from water temperature and speed sensors for display.

The GDS 20 can feed two displays simultaneously, so it is a good choice for dual-station boats. During our test, we used a single 2010C. Sounding information can be displayed in a split-screen mode with chart and navigation panels, or on standalone sonar pages with user-selectable graphic, symbolic and text panels. Depth, temperature and speeds are typically displayed in a text box.

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Moving left to right, a sonar image of the water beneath the boat is propagated, showing thermoclines, bottom contours and fish icons. Soft keys allow you to mark underwater waypoints and control operational and display parameters and alarms. Among the display selections is a dual frequency display that shows 200kHz and 50kHz data simultaneously to help you analyze echo returns.

The GDS 20 is available as a stand-alone upgrade for GPSMap 2006 and 2010 (monochrome and color) chart plotters. List price is $375; street price is about $300. A transducer will cost $150 to $300.

If you are starting from scratch, Garmin’s top-of-the-line color GPSMap 2010C (Field Test, June 2002) lists for $2,500 and is priced on the street around $2,200. So, for about $2,500 (including the cost of a transducer) you can assemble a high-performing, differential-ready, 12-parallel channel WAAS-capable receiver with a 10.4-inch diagonal high-resolution, color display and a dual-frequency, 500-watt sounder.

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Factory warranty on most Garmin equipment is one year.

Contact: Garmin International, (913) 397-8200; www.garmin.com

Click here to buy Garmin products.

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