Connecting the pigtail cable to the third-wire trawl cable
Before you can connect the third wire to the Communication Hub in the Trawl Unit, you need to splice the third-wire trawl cable to the pigtail cable provided with the FX80.
Prerequisites
•  The pigtail provided by Simrad as a part of the FX80 delivery
•  Heat-shrinking tubes with diameters to fit the outer diameter of the pigtail cable and third-wire cable (minimum total length is 70 cm)
•  Crimping sleeve with relevant set of pliers
•  Tinned braid foil (length of approximately 30 cm)
•  One tube with mastic
•  Heat gun
•  Isolation tape
•  Multimeter
Context
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The third-wire trawl cable comprises a core conductor surrounded by a grounding shield. Together, these form a coaxial cable. This coaxial cable is enclosed by a protective jacket and a flexible steel armour.
A Core conductor in the coax cable
B Insulation
C Shield
D Protective jacket
E Outer steel armour
It is very important that this splicing is done properly. The splice must be completely waterproof, and there must be no electrical short between the core conductor and the shield. The quality of this splice is vital for the operational performance of the FX80. There are many different third-wire cables available, and there are also many ways to splice the third wire to the pigtail. This procedure explains one method suggested by Simrad.
The trawl cable enters the Deployment Pack through a dedicated opening, and it is then supported by a strain-relief block in a special compartment. Both the core conductor and the shield in the third-wire trawl cable are connected to the pigtail provided by Simrad. The other end of the pigtail cable is provided with a watertight plug, which is connected to the Communication Hub. The design will not allow you to plug this into the wrong socket.
Important
The third-wire trawl cable must enter the Trawl Unit using an external strain relief with the proper dimensions. This item is not provided by Simrad.
Procedure
1 Remove the insulation on the coax cable and the pigtail cable.
a Remove the outer steel armour on the third-wire trawl cable to access the coax cable. You need to free at least 20 cm of the coaxial cable.
We have seen that this is done using a grinder, but you must then be very careful.
b Once you have removed the outer steel armour, the metal edges will be very sharp. Lift these edges of the armour to access underneath it, and apply several layers of tape – under the steel armour – for protection. After that, apply several layers of tape outside the steel armour and its edges to protect personnel and equipment.
c Remove the insulation on the coax cable (A), and fold back the grounding braid.
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Observe the illustration. You need to free approximately 80 mm of the coaxial cable, and approximately 20 mm of the core conductor must be stripped.
d Remove the insulation on the pigtail cable (B).
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Observe that the pigtail cable consists of one black and one white wire. The white cable is ground. In total you will need approximately 150 mm of cable. Cut off and strip the two cables as shown in the illustration. It does not matter if the ground conductor is longer than necessary — it will be cut to fit later.
2 Thread the heat-shrinking tubes as follows.
•  Onto the pigtail: One with a length of approximately 150 mm.
•  Onto the third-wire trawl cable:
–  First, one with a length of approximately 330 mm.
–  Then, another one with a length of approximately 150 mm.
3 Install the crimping sleeve.
a Take the stripped end of the black wire in the pigtail cable (B), and insert it into the crimping sleeve (C).
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b On the third-wire trawl cable, insert the stripped core conductor into the other end of the crimping sleeve (C).
Make sure that the two cables are laying next to each other inside the crimping sleeve, and that as little as possible of the stripped wires are shown outside the crimping sleeve.
Tip
If you have problems inserting the two stripped cables, you may need to remove dust and metal shavings from inside the crimping sleeve. As an alternative, use a crimping sleeve with a larger diameter.
c Crimp the sleeve from the centre and towards the end alternately on each side of the centre. Turn the cable 180 degrees after every second crimping.
d Clean the remaining cable insulation on each side of the crimping sleeve.
4 Install the first heat-shrinking tube (150 mm) that you previously threaded onto the third-wire trawl cable.
a Pull over the heat-shrinking tube (D), making sure that it covers the crimping sleeve, and also reaches as far as possible over the insulation on each side of the sleeve.
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Push the earthing braids on the coax cable well back.
Important
Make sure that you cover the crimping sleeve completely, and that no stripped conductors are visible.
b Shrink the tube (C) using the heat gun.
Keep the heat moving constantly to prevent overheating, and make sure that you heat the tube all the way around. Start in the centre of the tube. When it has shrunk, proceed towards each end, so that the glue is squeezed out. After heating, take a short break to let the tube cool down.
5 Install the heat-shrinking tube (150 mm) that you previously threaded onto the pigtail cable.
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a Pull over the heat-shrinking tube (E), making sure that this tube covers both the pigtail wires, as well as approximately half of the first heat-shrinking tube (D).
b Shrink the tube (E) using the heat gun.
6 Connect the ground conductors on the coax and pigtail cables with mastic.
a Apply a thin layer of mastic (F) around the end of the first heat-shrinking tube (D).
Make sure that it covers a large part of the heat-shrinking tube as well as a good part of the coax insulation.
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b Wind the ground conductor from the pigtail cable around the mastic.
c Push the cable screen from the coax cable (A) over the mastic (F) and the ground conductor from the pigtail cable.
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d Squeeze everything together to ensure good contact between the ground on the coax cable and the ground on the pigtail cable.
e Cut off excess ground wires, and make sure that no loose strands are left behind.
7 Wind tinned braid (G) tightly all over the joint.
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Make sure that each turn overlaps the previous turn. Press the end of the braid into the layer beyond, and remove any surplus.
Note
Make sure that the tinned braid is wound tight enough over the cable joint. This is important to ensure proper ground connection.
8 Clean the cables and the shrinking tubes properly.
9 Install the final heat-shrinking tube (330 mm) that you previously threaded onto the third-wire trawl cable.
a Pull over the heat-shrinking tube and centre it over the joint.
Make sure that it covers the entire length of the previous heat-shrinking tubes and the tinned braid.
b Shrink the final tube using the heat gun.
10 Complete the third-wire trawl cable installation.
a Use a multimeter to measure the resistance between the two pins on the pigtail plug.
Important
The resistance should be infinite or very large. If the multimeter indicates a short circuit, you must cut both cables and start from scratch.
b Mount the strain relief to the third-wire trawl cable.
Use the strain-relief block that sits in a special compartment on the outside cover of the Deployment Pack to hold the cable in place. Place the strain relief so that the splice between the third-wire trawl cable and pigtail cable sits inside the Trawl Unit. If necessary, adjust the thickness of the third-wire trawl cable by wrapping tape tightly around it.