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AFILS Field Strength Meter Instructions Version 1.3
Version 1.3 AFILS Field Strength Meter Instructions
the test source until the -9dB and -6dB LED's on the bargraph are both lit equally.
Note this frequency as the lower 3dB limit (typically around 100Hz).
Now increase the frequency of the test source to a frequency higher than 1kHz until
the 9dB and -6dB LED's on the bargraph are again both lit equally. Note this
frequency as the upper 3dB limit (typically around 5kHz).
Apply a representative source to any auxiliary input and set the corresponding
volume controls to a position where the meter bargraph also peaks into the green,
ideally to 0dB, as before.
Check that the audio quality is acceptable through the monitor headphones.
Rechecking the background noise with the AFILS system on
Ideally, the background noise should be re-checked with the AFILS switched on in
case there is any significant hum or other source of undesirable noise associated with
the AFILS itself. If this is the case then the cause of such noise must be found and
eliminated or minimised to an acceptable level no more than 27dB below the speech
peaks. The person testing the system should listen through the monitor headphones
whilst observing the meter bargraph (but do not exceed volume 4 on the LO range
setting).
Set the TONE (filter) switch to the NORM position
Move the RANGE switch to the LO position
Hold the meter upright with the top at the position a hearing aid is likely to be used.
If the background noise level is low (i.e. less than -36dB) and the loop system
struggles to produce 0dB, then a lower maximum level of -3dB is acceptable on
speech peaks.
Checking the AFILS frequency response
Switch the induction loop equipment on.
If not already done, set the drive control on the loop amplifier to ¾ or follow the
manufacturer's instructions.
Set the TONE (filter) switch to the FLAT position
Move the RANGE switch to the HI position
Hold the meter upright with the top at the position a hearing aid is likely to be used
Observe the LED bargraph.
Using a sinusoidal tone generator, apply a 1kHz tone to one of the amplifier or
mixer inputs and adjust the volume and/or gain control(s) so that the -6dB and -3dB
LED's on the bargraph are both lit equally.
Maintaining all volume and gain controls at these settings, reduce the frequency of
Specifications
Power:
1 x PP3 9V alkaline
Current drain:
20-50mA
Battery life:
>10 hours
Indicating ranges:
-51dB to -24dB and -24dB to +3dB with respect to
0.56A/m
Indicator style:
BBC/EBU Peak Programme Meter (3ms attack, 650ms
decay)
Resolution:
3dB
Absolute accuracy:
±
0.5dB @ 0dB (0.56A/m) and -27dB (25mA/m)
reducing to
±
1.5dB @ -24dB (35mA/m) and -51dB (1.6mA/m)
Filter characteristics:
NORM: -3dB @ 630Hz & 5kHz
FLAT: -3dB @ 40Hz & 14kHz
Headphone monitor:
max 2 x 19mW into 32 ohms
Relevant Standards:
BS7594, BS6083, BS6840, BS EN 60118
At the end of their useful life, the packaging, product and batteries
should be disposed of via a suitable recycling centre. Do not dispose
of with your normal household waste. Do not burn.
This product is RoHS compliant.
