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erence sensitivity level (-112 dBm) with a correctly functioning

mobile.

TETRA mobiles need to be able to receive a signal from the base

station (test set) that meets or exceeds the 'minimum Rx level for

access'. The default value for this parameter on the IFR 2968 is

-125 dBm, and you should ensure that this value is set prior to per-

forming receiver sensitivity tests, in order to avoid call dropping.

QQ33..44::

Why doesn't 'TT' RF Loopback work with my mobile?

AA33..44::

You may need to perform a Test Mode Registration before-

hand so that the mobile is enabled to respond to the TT loopback

commands. This may require you to perform an enabling action

on the mobile (e.g. entering an access code) and to send a TT test

mode confirmation from the IFR 2968. Refer to the 2968 TETRA

Supplement issue 10, chapter 4, pages 41 and 12 for details. Refer

to the mobile manufacturer for specific details of enabling TT test

mode on the mobile.

The mobile may not support TT test mode registration or TT RF

Loopback, in which case you will not be able to perform

BER/RBER /MER tests on the speech traffic channel, and you will

not be able to include receiver sensitivity testing in automatic test

programs. Refer to the mobile manufacturer for further informa-

tion.

QQ33..55::

How do I test receiver sensitivity if a mobile does not sup-

port TT RF Loopback?

AA33..55::

If the mobile does not support TT RF Loopback, you will not

be able to test receiver sensitivity automatically as part of an

autotest program, and you will not be able to test it manually as

part of normal functional and parametric testing using registration

and call set-up. To test the receiver you will need to set both the

mobile and the IFR 2968 to operate in T1 test mode. If the mobile

supports T1 Loopback, you can perform a manual measurement

of sensitivity using the IFR 2968. If the mobile does not support

T1 Loopback, you will need to use the mobile's internal BER/MER

measurement or external BER / MER measurement using a suit-

able application program supplied by the mobile manufacturer.

Refer to the 2968 TETRA Supplement issue 10, chapter 4, pages

34 and 36 to 39 for details of operating the IFR 2968 in T1 test

mode. Refer to the mobile manufacturer for details of operating

the mobile in T1 test mode and internal or external BER/MER

measurement applications.

QQ33..66::

What is the difference between 'TT' test mode and 'T1' test

mode?

AA33..66::

TT' (TETRA Test) is a mode of operation that may be imple-

mented in a TETRA mobile, in which certain additional functions

for testing are enabled, but otherwise the mobile operates as nor-

mal for registering and setting up calls. The mobile manufacturer

may also decide to modify, restrict or disable certain functions

when in TETRA Test mode, e.g. group attachments and security

functions may be disabled, and the mobile may adopt a special

test identity rather than its normal network identity.

TT mode provides TT RF Loopback and Test Mode Registration. TT

RF Loopback is operated by the IFR 2968 sending TETRA sig-

nalling commands to the mobile via the usual RF connection

when the mobile is in a duplex call. Test Mode Registration is an

additional signalling sequence performed after normal

Registration, which confirms the use of TT test mode in the mobile

and obtains information from the mobile that is essential for test

automation (TEI, power class and receiver class).

T1 test mode is a special mode of operation that is required to be

implemented in a TETRA mobile submitted for conformance test-

ing according to ETSI EN 300 394-1 (TETRA Radio Conformance

test specification). T1 test mode may also have applications in

manufacturing or service testing. T1 test mode is a one way con-

trol mode, in which the IFR 2968 generates a signal to stimulate

and control the mobile under test, but does not receive any sig-

nalling from the mobile. There is no protocol involved in T1 test-

ing, other than the generation of the T1 signal control parameters.

There is no registration and no call set-up, and the mobile does

not send any signalling information in T1 test mode.

Flags in the T1 signal control information can instruct the mobile

to turn its transmitter on or off and to transmit normal bursts or

control bursts at a specified power level. The control information

also informs the mobile of the T1 signal type (TCH/7.2, SCH/F or

TCH/2.4) so that the mobile can receive and decode the infor-

mation accordingly. Another flag in the control information can

instruct the mobile to re-transmit the received data (T1 RF

Loopback).

QQ33..77::

How do I access T1 test mode in the mobile under test?

AA33..77::

There is no standard mechanism for this, and the mobile

may not necessarily support T1 test mode. Typically you may need

to know a special key sequence or you may need a PC applica-

tion for configuring, aligning and testing the mobile. Access to

such facilities may well be restricted by the mobile manufacturer

and you should contact the mobile manufacturer or supplier to

discuss the appropriate level of access to test and diagnostic facil-

ities.

QQ33..88::

How do I test the mobile receiver if I have no access to TT

loopback or T1 test mode?

AA33..88::

TT loopback or T1 test mode should always be used where

possible, since they provide the most objective and repeatable

test of receiver performance. TT loopback is the most convenient

as it can be automated. However, if the mobile does not support

these modes, or if you cannot obtain access to the manufacturer's

test modes, it is possible to perform an approximate test of receiv-

er sensitivity using a conventional SINAD test. For this you will only

need access to a suitable audio output from the mobile, typically

a loudspeaker or accessory earpiece socket. Note that this will

also test the quality of the mobile's audio circuitry.

If the mobile has adequate RF sensitivity, you should be able to

determine that the SINAD is satisfactory at the reference sensitiv-

ity level. However, due to the use of the TETRA codec, the audio

signal degradation at low RF levels behaves differently from ana-

logue RF signals. This method will not work well at RF levels below

the reference sensitivity level as the BER of the TETRA signal

increases, particularly when errors occur in the Class 1 bits or

when errors in the Class 2 bits cause erasure of speech frames.

Refer to the 2968 TETRA Supplement issue 10, chapter 4, pages

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 ... 23 24

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