Pulse Duration
The pulse duration can be selected according to the current range and what kind of targets you are looking at. The longer range you wish to use, the longer pulse duration should be selected. However, when using CW transmissions a long pulse duration will reduce the resolution. It will also cause the ST90 system to transmit less frequent.
Further, increased pulse duration will cause reduced source level when using consecutive transmissions. For example, if the ST90 system is set up to use one horizontal ping and two vertical pings these are transmitted in series. The first ping will reduce
the voltage level on the output capacitors, and this reduces the source level on the following transmissions.
Longer pulses will also increase the blind zone close to the transducer and increase the reverberation level.
For these reasons, the use of long pulse durations may not be the best choice.
For CW (Continuous Wave) transmissions:
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Long pulses provides longer detection range. They make the ST90 system less sensitive for noise, but offer lower range resolution. |
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Short pulses provides shorter detection range. They make the ST90 system more sensitive for noise, but offer higher range resolution. |
For FM (Frequency Modulated) transmissions:
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Long pulses provide longer detection range, and the range resolution is independent of the pulse duration.. |
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Short pulses provide shorter detection range, and they make the ST90 system more sensitive for noise. |
Bandwidth function
The bandwidth used by the frequency modulated transmissions is controlled by the Bandwidth function. Each frequency modulated transmission ("ping") from the ST90 system consists of a frequency sweep around the centre frequency. The difference between the lowest and the highest frequency in each transmission is referred to as bandwidth. The chosen bandwidth will spread equally to both sides of the centre frequency.
The bandwidth function does not apply to CW (Continuous Wave) transmissions.
Open this function from the Active menu.
Frequency function
Use the Frequency function to specify the centre frequency for the frequency modulated (FM) transmissions (pings) and the operating frequency
for the continuous wave (CW) pings. You can change the frequency in predefined steps from a "start frequency" to an "end frequency".
Open this function from the Active menu.