EN 55024:1998/IS1:2007

SLOVENSKI STANDARD
01-februar-2008
Oprema za informacijsko tehnologijo - Karakteristike odpornosti proti motnjam -
Mejne vrednosti in merilne metode
Information technology equipment - Immunity characteristics - Limits and methods of
measurement
Einrichtungen der Informationstechnik - Störfestigkeitseigenschaften - Grenzwerte und
Messverfahren
Appareils de traitement de l'information - Caractéristiques d'immunité - Limites et
méthodes de mesure
Ta slovenski standard je istoveten z: EN 55024:1998/IS1:2007
ICS:
33.100.20
35.020
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 55024/IS1
Interpretation Sheet 1
EN 55024:1998
English version
___________
Foreword
This Interpretation Sheet to the European Standard EN 55024:1998 + A1:2001 + A2:2003 was prepared
by the Interpretation Panel of the Technical Committee CENELEC TC 210, Electromagnetic compatibility
(EMC). The text of the draft was submitted to the Unique Acceptance Procedure (as prISA to prISE) and
was approved by CENELEC on 2007-06-22.

Annex A Telecommunications terminal equipment
Application of Annex A to personal computers used as TTE.
PCs are multi-function equipment by nature. EN 55024 requires the testing of all functions of multi-function
equipment in order to establish compliance. Modern PCs have the capability of being used as VoIP or
video TTE.
Question 1:
How should the testing be performed when PCs are used in this mode ?
Interpretation 1:
As the standard modern PC will support VoIP and video conferencing, it has several functions as TTE in
addition to its functions as self-contained ITE. Compliance with EN 55024 is dependent on all functions of
a product being compliant.
The interpretations given for questions 4 and 5 on the testing of VoIP telephony products and video
conferencing systems to EN 55024 can equally be applied to these functions of PCs.

Clause A.1 Telecommunications terminal equipment (TTE) having an analogue interface
Clause A.2 Telecommunications terminal equipment (TTE) having a digital interface
Dealing with echo-cancelling within TTE products.
Question 2:
The requirements for acoustic and line noise measurements assume that the emitted tone and the line
noise signal are at a constant level over time. In practice echo-cancelling functions have been observed to
recognise a 1 kHz audio tone as an echo and hence attenuate it, sometimes with several stages of
attenuation. Should echo-cancelling be turned off ? If not, what is timing of the measurements from the
application of the AM to the CW?
Interpretation 2:
Where echo-cancelling is employed, turning it off may not always be possible. Echo-cancelling would
potentially provide a benefit the TTE in real-life performance by attenuating any demodulated noise. As
generally stated in EMC performance criteria the compliance of the EUT must be assessed when
“operated as intended”. Also, Article 4 (b) of 89/336/EEC states that apparatus shall be so constructed
that “the apparatus has an adequate level of intrinsic immunity to electromagnetic disturbance to enable it
to operate as intended.”
For these reasons, echo-cancelling functions shall not be turned off during testing. (Due consideration has
been given to similar standards, such as ETSI 301 489-7, where there is a requirement to turn off echo-
cancelling prior to testing, but it considered that for apparatus covered by EN 55024, this is not
appropriate.)
Reference levels shall be established before the echo-cancelling function operates. If this is difficult to
observe due to the speed of the echo-cancellation, then acoustic measurement equipment shall be set to
record the maximum acoustic level from the instant of the -40 dBm/dBm0 injection on the line.
Good echo-cancelling attenuates a demodulated signal rapidly, and is desirable. Echo-cancelling that
takes some time to become effective would cause annoyance. The dwell time typically used for 1 % steps
-3
at a sweep rate of 1,5 x 10 decades/second is approximately 3 s, and this offers a practical solution for
determining the appropriate time of measurement.
Therefore in order to assess the effectiveness of the echo-cancelling and to establish compliance, the
dwell time (i.e. the time during which the carrier frequency is amplitude modulated with 1 kHz prior to
measurement) shall be 3 s. The end of the dwell time indicates the start time of the demodulation
measurements (in both directions). The amplitude modulation shall remain on during the demodulation
measurements.
Test laboratories are encouraged to ensure the time taken to make the demodulation measurements is as
short as possible (less than one second) and they shall record and report the time taken for the
measurements. The total dwell at each test frequency is therefore 3 s plus the demodulation measurement
time.
– 3 – EN 55024:1998/IS1:2007
Clause A.1 Telecommunications terminal equipment (TTE) having an analogue interface
Clause A.2 Telecommunications terminal equipment (TTE) having a digital interface
Dealing with the mute function within TTE products.
Question 3:
One of the functions of a typical conference/speaker phone is the ability to mute the near end microphone.
If a TTE product has a mute function then it has two modes of operation; “muted” and “un-muted”.
A mute function could be implemented by a switch on the microphone wire, or by a software instruction to
the DSP within the TTE to produce and maintain a degree of isolation.
If TTE is to be tested with the mute function on, then circuitry which could cause a demodulation failure
may actually be isolated.
If TTE is to be tested with the mute function off, then the audio tone from the speaker is typically less
stable than with mute on. This sometimes makes the establishment of the audio reference level of
method 2 difficult.
What modes of operation should be tested and what can be done to establish a constant reference level
when a product has a mute function?
Interpretation 3:
There are clearly two operation modes to consider when a call is established - “Muted” and “Un-muted”.
When testing “Muted” then mute should be on throu
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