. Basic methods for the calibration of sonar equipment. RECEIVING 29. : 9. tliiiiiil ciiui\.ilcnl l«i .1 loiii; line. (lut'iicN' l):uicl ol 1 cycle ami a icinptraimc of 20 C: ii has the \ aliie X 10--")-, (11) where )(. is the eqiiixalent series resistance ol the device. In the practical case there are two distinct condi- tions to be considered; calcidated threshold and meas- ured threshold. Calculated Threshold In the case ol low-impedance h\choj)hones, iisiialh of the electrod)namic or magnetostrictive type, the active luiit usually is directly connected 10 a lini-. If this
. Basic methods for the calibration of sonar equipment. RECEIVING 29. : 9. tliiiiiil ciiui\.ilcnl l«i .1 loiii; line. (lut'iicN' l):uicl ol 1 cycle ami a icinptraimc of 20 C: ii has the \ aliie X 10--")-, (11) where )(. is the eqiiixalent series resistance ol the device. In the practical case there are two distinct condi- tions to be considered; calcidated threshold and meas- ured threshold. Calculated Threshold In the case ol low-impedance h\choj)hones, iisiialh of the electrod)namic or magnetostrictive type, the active luiit usually is directly connected 10 a lini-. If this line has appieciahle lenglh, ils impedance must be matched at both terminals, sinie otherwise irregularities in response aie inirodiued due to reflec- tions in the line itself. Neglecting attenuation, the circuit may then be 1 epresented as in Figme 9. Here câ is the generated open-circuit signal \ oltage, eâi is the generated noise xoltage in the resistance of the hydrojjhone ?â , and e,,.^ is the generated noise volt- age in the terminating resistance Vj,. Reactances in the circuit are omitted for the sake of simplicity. F,, is the noise \oltage and 1% is the signal voltage applied to the input of the measuring circuit, assinned to be the grid of the amplifier. The noise voltage applied to ihc grid due to e,,^ is The noise voltage applied to the grid due to e,,., is v., = f-^^y The rms noise voltage Vâ applied to the grid due to both eâi and e,,-, is obtained by adding the two fluc- tuating noises at random pliase, thus v,r- = e,A^^y + <'.4^âS^' (12) When the line imjjedance is matched at the two ter- minals, ij, = r. Then by etjuation (11) above, (',,1 = eâ- = (',,, so that r. - (^ . ^ V2 (13) IIk' signal \oltage Vg applied at the griil is then one- half the \oltage generated by the hydrophone, From the abo\e relation T,, the signal \oltage gen- erated by the hydrophone, ecpials Vâ, the noise volt- age in the matched circuit, when 1 eâ (14) The other possi
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