A sonde is a unit that can be attached to a range of equipment including drain rods, boring tools and sewer cameras; it transmits a signal (8 kHz, 27 kHz or 83 kHz) which is then traceable by the receiver set at the same frequency. The different frequencies allow easier tracing under different conditions.
There are two sizes:
- Type 1: 44mm diameter 360mm in length
- Type 2: 26mm diameter 230mm in length