Basic unit of the borehole hydrophone string type 1 is the hydrophone F-24 together with two-conductor signal cable on a cable drum. Standard cable length is sufficient for a borehole depth of about 100 m. Other cable lengths up to 330 m can be delivered on request.

By means of a pulling and carrier rope made of polypropylene up to 24 hydrophones can be assembled at user specified spacings to form a hydrophon string for each field operation.

A sinker bar at the bottom end of the carrier rope serves to tight the hydrophone string when running into borehole. Each hydrophone consists of an oil coupled piezoceramic pressure transducer and a preamplifier supplied from a common battery and matching box via signal cable. A multiconductor cable connects the box with the seismic recorder unit.