I-AMP GPT 60-IV User Manual page 7

INDUCTION LOOP AMPLIFIER
-AMP
Double Loops:
Some installations require the use of a double loop cable on the output. The double loop is easily
implemented with standard figure-8 cables. The double loop increases the field strength for a given output
current by 12dB, however the frequency response can suffer. This configuration also allows for increasing
the overall loop resistance (for small loops) or reducing the current requirement by a factor of 4. Note also
that the length of the induction loop cable will increase and the induction loop cable cross sectional area
may need to be increased to allow for a maximum DC loop resistance of 1.8Ω.
INDUCTION LOOP AMPLIFIER
-AMP GPT 60-IV
INDUCTION LOOP AMPLIFIER
-AMP GPT 60-IV
Metal Loss:
The Induction loop cable does not present a constant load at all frequencies of interest. The impedance of
the cable increases with frequency. This will not cause any problems for an induction loop amplifier since it
will automatically increase the output voltage, at high frequencies, to compensate and produce the required
current at all frequencies, independent of cable loading. However, the magnetic field generated in the loop
will not only be dependant on the loop current, but the structure surrounding the loop. Metallic structures
create greater loading of the magnetic field at high frequencies. This can be compensated by increasing the
high frequency levels input to the induction loop power amplifier with a graphic equalizer or other filter.
G p t 6 0 - I v
LOOPS OF EQUAL SIZES
+
GPT 60-IV
-
+
USE OF FIG 8 CABLE
- FOR DOUBLE LOOPS
+
-
~ 7 ~
TRACER ONE END OF CABLE RUNS
AROUND PERIMETER
TRACER
OTHER END OF CABLE RUNS
AROUND PERIMETER
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