ACCESS/A A711 L-Series Installation Manual 09RE416
Technisonic Industries Ltd. Copyright 1996, 1997, 2010, 2011 BY TiL ALL RIGHTS RESERVED Page 1-5
1.6
SYSTEM LIMITATIONS
A summary of the relevant system limitations is given below.
1.6.1
Power Limitations
With Standard Set-up, which consists of six headsets connected, a power output of not less than
332 mW is delivered per headset (as represented by 150 ohms) provided that the Direct Alert
Input is terminated in not less than 600 ohms and that nominal input voltages are applied
at the applicable channel inputs. Nominal microphone input: 100 mV
rms
; Nominal
Communications/Navigational Input: 5.5 V
rms
.
1.6.2 Frequency Response Limitations
In accordance with the provisions made in RTCA/DO-214 Sections 2.8.1 and 1.5.1 the
communications transmit out and receiver channels (communications and navigational) possess
an effective bandwidth of 300 Hz--3000 Hz with a maximum amplitude variation of 3 dB within the
frequency range.
1.6.3 Crosstalk Limitations
To ensure that the crosstalk specifications are in accordance with the applicable sections of DO-
214, it is essential that 1) manufacturer’s maximum microphone input voltage of -4.7 dBu not
be exceeded in order to avoid jeopardising input to microphone output crosstalk results,
particularly at the low frequency end, 2) in the instance where only two access units are daisy
chained via their ICS tie-lines, a resistor of not greater than 600 ohms must be maintained
across the ICS tie-line in order to avoid jeopardising station to station crosstalk results in Rx
mode at the high frequency end.
The phenomenon of music appearing at the headset of the Second Station Panel (SSP or unit at
which the crosstalk is measured) for station to station crosstalk considerations is a limitation of the
A711L and for which crosstalk at high frequencies (6000 Hz and greater) can fall below 65 dB of
attenuation. However music for most intents and purposes may be considered an optional feature,
which may be turned off without a negative impact on the essential functioning of the access units.
Further, valid station to station crosstalk measurements were quoted in respect of a half power
level at the headset at the First Station Panel (FSP or unit from which the crosstalk originates) as
opposed to a half power level at the speaker output of the FSP because it is envisioned in the
latter scenario that the substantial speaker level (which will also necessitate very large signal
levels at the FSP headset) will have an impact on the listener at the SSP whether a crosstalk
signal appears at the SSP listener’s headset or not.
When multiple transceivers are selected for simulcast operation, they are bound together at the
station output, and thus are also bound together for other stations as well, defeating cross-talk
measurements. All measurements are based on single transceiver TX selection.
