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Loop patterns
A loop pattern laid on the floor is a low cost
method to reduce over-spill by providing more
even field strength compared to the usual
single turn of cable laid around the room's
perimeter. The basic pattern looks like the
diagram below:
Each pattern should be considered as a many
pronged fork. The pattern should be spaced
approx. 2m from nearest wall / next pattern,
prongs of the fork should be spaced approx.
2m apart and should be approx. 2m wide,
prongs should extend to approx. 3/4m of base
of fork.
Assume the cable is being run around the
edge
of
a
room
for
cable
diameter
calculations, as the pattern restricts the
amount of power which can be fed into the
loop. The large black arrow shows clockwise
direction of loop. Break into pattern at any
point to connect PDA unit.
Loop patterns
Large areas and multiple rooms
Use several loop patterns, each pattern must
be connected to a separate loop amplifier.
When laying out patterns, ensure each is 90
degrees out of phase with its neighbours as
per the following diagrams which show a two
storey building:
Note. For a two storey building the same loop
position on different floors is also 90 degrees
out of phase.
Non-rectangular rooms
Layout as per a basic pattern and step back
the prongs to the shape of the room.
Page 6
Doc No. DCP0001751 JC 09/01/03 rev2
Installation
Read this manual thoroughly before starting
installation, the following procedure should be
used.
1.Install the loop (see page 6)
2.Before connecting a loop to the amplifier
use, a multimeter to check the loop is not
shorted to ground at any point, (it will almost
certainly damage the amplifier if it is).
Remove approximately 6mm of the outer
insulation from the cable. Connect the loop
cable to the amplifier by inserting a terminal
screwdriver into the small rectangular hole
above the cable insertion hole, this will open
the insertion hole and allow the cable to be
pushed into the connector. Remove the
terminal screwdriver and the connector will
close
gripping
the
cable.
Ensure
connector is gripping the conductor in the
cable and not the insulation.
3.Connect music or speech input signal to the
amplifier. The peak line level of this signal
should be approximately 1V.
4.Set the DIP switches as required.
5.Ensure input levels controls and drive
control are fully anti-clockwise.
6.Connect mains lead to the amplifier and
ensure the power LED (green) lights.
7.Increase the input level controls until the red
'limit' LED is just flashing. If you are using
both inputs the level controls act as a simple
mixer.
8.Adjust the drive control until the red clip LED
just lights during periods of high signal level
(when the limit led just lights).
9.Using an induction loop receiver (eg SigNET
Rxti2 or a field strength meter), listen to the
signal inside the loop. It is also advisable to
check the system with a field strength meter.
Please note that the orientation of the field
strength meter may influence the reading.
Mains Hum
Background hum can sometimes be heard
when testing an installation especailly when
testing with a induction loop receiver. This is
not caused by the loop system and will NOT
normally be heard by hearing aid users, due to
built in filtering in most hearing aids. The
source of mains hum is most likely to be (50
Hz) mains wiring, particularly in old buildings
where Live and Neutral cables may take
different routes, thus creating an induction
loop radiating at 50Hz. If the client complains
of mains hum simply switch off the amplifier to
prove that the source is unrelated.
Input connections
Two input connectors are standard 3.5mm
mono jack sockets. Both are mic or line
selectable dependant upon the DIP switch
positions, use the following chart or see the
back of the unit which has the switch positions
next to the switches.
Switch
Off
1
Line
Microphone
2
Phantom Off
Phantom ON
3
Line
Microphone
4
Phantom Off
Phantom ON
the
Phantom power is supplied - 2.5V, 0.25mA
maximum.
Page 3
Doc No. DCP0001751 JC 09/01/03 rev2
On
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