Simrad TV80, Reference Manual

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• Pulse duration
You can choose from 64µs (CW) 128µs (CW), 512µs (FM), 1024µs (FM) and 2048µs
(FM).
The
Pulse Duration
setting specifies the current duration ("length") of the transmitted
pulse. The duration ("length") of your transmitted pulse is very important to how you
can detect fish.
– A short pulse duration gives you a very fine vertical resolution.
– A long pulse duration throws a lot more energy into the water, and the digital filters
used by the receiver are narrower.
The shorter pulses offer a higher resolution and a shorter blanking zone, but they are
more affected by noise. We recommend using short pulse length on low trawls, in the
tunnel and at the cod end. The pulse lengths 512µ, 1024µs and 2018µs use FM sweep
(Chirp) technology and give high resolution even if the pulse length is long. However,
the longest the pulse, the largest the blanking zone. We recommend using 512µs (default
value) and longer pulses on trawls from 15m and more height.
• TVG
You can choose from 20dB, 30dB, 35dB and 40dB
When an acoustic pulse is sent through the water, it will gradually lose its energy. The
greater the distance between the hydrophone and the target(s), the greater the loss of
energy.
TVG
(Time Variable Gain) compensates for the loss of acoustic energy due to
geometric spread and absorption.
20dB gives a weaker amplification from the bottom.
40dB gives more amplification from the bottom, but also from single fish.
The TVG compensation is expressed as a logarithmic curve.
• Gain
You can choose from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16
The purpose of the
Gain
function is to adjust the echo level in the TV80 presentations.
In combination with TVG value, select the best setting for your fishing scenario. 10 is the
default value. Gain is a linear function.
• Offset
Offset can be used if you are more interested on details from, for example, the centre of
the trawl and down to the bottom rather than the whole trawl opening. Instead of having
the echogram starting from the sensor, you make it start from a distance from the sensor.
This will help you focus on the part of the trawl that is most important for you.
• Learn mode
Simrad TV80 Reference Manual