The Garmin GT20-TM is the most common transducer included with quite a few Garmin fish finders. There actually are two versions for it, the 010-01960-00 which has a 4-pin connector, and the 010-01960-01 featuring an 8-pin connector. The page here links to the 010-01960-00, the one with 4-pin. Both have 20 ft. (6 m) of cable, a transom mount (that’s what the “TM” stands for), and an internal water temperature sensor. The transom mount is designed for a boat’s transom between 0° and 70°.
Frequency and Coverage
The Garmin GT20-TM is a dual-beam transducer. Its supported frequencies are 77/200 kHz for traditional CHIRP sonar, ahd 455/800 kHz for ClearVü. The CHIRP ranges for the traditional beams are not specified, but for the Cv, they are 435-475 kHz, and 800-840 kHz.
For the 2D traditional CHIRP, the transducer uses two conical beams. Their coverage is 15° @ 200 kHz, and 45° @ 77 kHz. The greatest depth for the 2D CHIRP sonar can be achieved with the 77 kHz beam which can reach 1,900 ft. (579 m).
For ClearVü, the GT20 also uses two beams, but they are oval-shaped, very thin fore-to-aft. Their coverage is 53°x2.5° @ 455 kHz and 29° x 1.6° @ 800 kHz. The maximum depth capability for the ClearVü sonar that can be reached with this transducer is 750 ft. (228 m).
Echosounder Compatibility and Other Accessories
The Garmin GT20-TM is compatible with all Striker and ECHOMAP units. However, if you pair it with a “SV” unit, you won’t be able to use the SideVü mode with it because it doesn’t have the internal SideVü element. This also stands for the newer Garmin UHD units; the GT20 does not support the UHD sonar mode.
In terms of accessories, there are quite a few available for this transducer. The transom mount is usually included with it, but there are several other mount possibilities. For example, there is a trolling motor mount (010-12105-10), a kayak in-hull mount (010-12357-00), a suction cup mount (010-11849-17), and also a heavy-duty metallic mount (010-12006-11).
Three extension cables are available for the GT20 transducer. These are: 010-11617-10 (4-pin, 10 ft.), 010-11617-50 (8-pin, 10 ft.), and 010-11617-52 (8-pin, 30 ft.). There is also an 8-pin transducer to 4-pin unit cable adapter (010-12719-00).