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the PTT pressed. If you are testing in Direct Mode, you will not be

able to set up a duplex call, so you should simply release and re-

press the PTT to continue measuring.

QQ22..88::

Why does my TETRA mobile or base station exhibit exces-

sive vector error?

AA22..88::

A number of causes can contribute to vector error per-

formance exceeding the limits, so the 2968 provides further diag-

nostic displays to track down the cause of a vector error failure,

including the constellation diagram, rotated vector diagram, and

particularly the vector error vs. time displays with separate resolu-

tion of the phase error and magnitude error components. Vector

error that is predominantly due to phase error may be a symptom

of an unstable transmit frequency, i.e. the frequency error is vary-

ing during a single burst period, maybe because of oscillator set-

tling problems. Vector error that is predominantly due to magni-

tude error may be a symptom of an unstable power level, i.e. the

power is drooping during a single burst period, maybe because

of an inadequate power supply. If the RMS vector error is low but

the peak vector error is very high, this may be a symptom of incor-

rect power ramping by the mobile - check the power profile dis-

play. These functions are accessed via the DUPLEX TEST mode.

Refer to the operating manual Phase 3.2TETRA supplement issue

10, chapter 8, for details of using these functions.

QQ22..99::

Can the 2968 measure Adjacent Channel Power (ACP)?

AA22..99::

No. The 2968 performs the routine measurements of the

on-channel transmitted signal. TETRA ACP is a specialised high

dynamic range measurement for conformance testing and some

manufacturing test applications which can only be performed by

the IFR 2310 TETRA Signal Analyzer. Refer to the IFR 2310 data

sheet for details of measurement of ACP and other specialised

measurement functions.

However, the IFR 2968 can be useful in conjunction with the IFR

2310, with the TETRA mobile connected to both instruments via a

power splitter. The 2968 is used to stimulate the mobile so that it

can register and set up a call at a particular frequency and power

level, whilst the 2310 is used to make the high dynamic range off-

channel measurements.

QQ22..1100::

Can the 2968 power measurement compensate for

cable loss, attenuators, splitters?

AA22..1100::

Yes. The compensation applies to all 2968 power meas-

urements, not just TETRA, hence it is set up under the main instru-

ment set-up menus rather than the TETRA system specific menus.

Press the HELP / SET-UP hardkey then the softkeys SET-UP, TEST

OPTIONS, rf port setup, then set the "receiver level offset" for the

required compensation. Negative values compensate for an

external loss, positive values compensate for an external gain.

QQ22..1111::

Why does the power reading show a reverse video aster-

isk next to it?

AA22..1111::

This is a warning that the 2968 has been set to compen-

sate for an external gain or loss (see A2.10 above). If the com-

pensation is no longer required, reset the receiver level offset to

0 dB.

QQ22..1122::

Can the IFR 2968 measure directional ("through-line")

power?

AA22..1122::

Yes. IFR supplies a high accuracy directional power head

as an optional accessory, part number 54421/003, enabling you

to measure forward and reverse power and VSWR. You will also

need the accessory socket adaptor 46884/645 to use the power

head with the IFR 2968.

Section 3 Q&A: Testing mobile and base station

receivers

QQ33..11::

Can the IFR 2968 test the receiver sensitivity of TETRA

mobiles?

AA33..11::

Yes. A variety of different test signals and test methods are

provided in the IFR 2968 to support the capabilities and testing

requirements of various TETRA mobiles.

• TETRA Test mode (TT) RF Loopback provides automatic

or manual testing of receiver sensitivity (BER or MER /

RBER) on the three different sensitivity class bits on the

speech traffic channel (TCH/S), in a similar manner to the

standard GSM method.

• Radio Conformance Test (T1) RF Loopback provides

manual testing of receiver sensitivity (BER) on the T1Type

1 (TCH/7.2) signal. The IFR 2968 generates the PRBS

data and measures the BER of the received signal

returned by the mobile under test.

• Radio Conformance Test (T1) signal generation provides

the test source for a mobile to measure its own BER or

MER, or for an external device to measure the BER / MER

of the data recovered by the mobile under test. The IFR

2968 generates the PRBS data for three different T1 sig-

nal types: Type 1 (TCH/7.2), Type 2 (SCH/F) and Type 4

(TCH/2.4).

• 1 kHz tone encoded speech signal generation and audio

SINAD measurement provide manual testing of receiver

sensitivity on the speech traffic channel (TCH/S) for

mobiles that do not support loopback or where the user

is unable to access the manufacturer's test functions for

measuring BER.

QQ33..22::

How do I measure receiver sensitivity using 'TT' RF

Loopback?

AA33..22::

In Autotest the IFR 2968 performs the test(s) automatical-

ly. In manual test mode, you need to set up a duplex call and then

select BER TT Loopback or RBER TT Loopback. Depending on the

type of mobile, you may need to perform a Test Mode Registration

beforehand. Refer to the 2968 TETRA Supplement issue 10,

chapter 4, pages 6, 34, 36, 37 and 41 for details.

QQ33..33::

Why does the mobile drop the call while measuring receiv-

er sensitivity?

AA33..33::

You may have set the RF GEN LEVEL too low for too long,

or you may need to adjust the 'minimum Rx level for access' sys-

tem parameter. TETRA mobiles need to be able to receive infor-

mation from the base station (test set) signal in order to maintain

a call; if the RF generator level is reduced too far, the error rate

may be too high for the mobile to reliably decode the base station

(test set) signal. This should not normally be a problem at the ref-

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