Aeroflex 2050T SERIES Especificaciones descargar pdf (Pagina 18)

Firstly, use the 2968 in base station test mode ([SYSTEM] [TETRA

base], requires Option 31 TETRA BS) to determine the frequency

of the base station. Select channel plan NO PLAN ([SET-UP] [chan-

nel plan] [NO PLAN]) and go to [MANUAL] mode. Ensure that your

antenna is connected to the TNC port in 2-port duplex mode with

maximum sensitivity (refer to 'Off-Air Base Station testing' in the

2968 Phase 3.2 TETRA supplement issue 10, chapter 5, page 8).

Use [expected power] and repeated [-10 dB step] then [return] to

set expected power level of -40 dBm. Use the 2968 spectrum

analyser in expanded mode with markers on (2968 Phase 3.2

TETRA supplement issue 10, chapter 8, pages 2, 7 and 8) to

locate the frequency of the base station signal. Initially set a wide

span to cover the possible frequency range (e.g. REF FREQ 405

MHz span 5 MHz/div will cover the range 380 MHz to 430 MHz).

Use the [peak find] or [move marker] functions and the [set ref to

M1] function to home in on the local base station signal. Repeat

this process with reduced span widths ([  /div ]) until the char-

acteristic TETRA modulated signal is centred on a span of

5 kHz/div. Make a note of the REF FREQ, adjusting it as required

so that it is an exact multiple of 6.25 kHz.

Secondly, return to SYSTEMS mode, which overrides the DUPLEX

mode settings, and enter the REF FREQ value as the TX FRE-

QUENCY and press the [all slots] softkey. The 2968 should

receive, demodulate and decode the base station signal and dis-

play the MCC, MNC and BCC values ('Base station identity infor-

mation', page 5 of chapter 6 of the 2968 Phase 3.2 TETRA sup-

plement issue 10). Make a note of the MCC, MNC and BCC val-

ues.

Thirdly, return to TETRA mobile test mode ([SYSTEM] [TETRA

mobile]), and set up the 2968 System Parameters with the same

MCC and MNC as the local base station. It is advisable to set a dif-

ferent value of BCC (but not zero) to guard against co-channel

reception of the real base station by the mobile. Calculate the

channel plan and channel number from the base station frequen-

cy (see A6.12 below) and set up the 2968 with the channel plan

and control channel number to match the local base station.

Finally, connect the TETRA mobile to the 2968 (not forgetting to

reset the RF SELECT to the N-type port in 1-port duplex mode)

and set the 2968 RF GEN LEVEL to a high level (e.g. -50 dBm) to

guard against inadvertent reception of the local base station sig-

nal (see warning on 'RF Interference' in the 2968 Phase 3.2

TETRA supplement issue 10, chapter 2, page 2). Switch on the

mobile and it should now register to the IFR 2968. The mobile

may also be capable of scanning the frequency band to find the

2968's MCCH on a different channel if it can be screened or oth-

erwise prevented from receiving the local base station signal.

QQ66..1122::

How do I convert a frequency in Hz to a TETRA channel

plan and channel number?

AA66..1122::

There is a straightforward calculation to do this. When you

are testing a base station or a direct mode mobile, or a mobile in

T1 test mode, you do not need to convert the frequency to a

channel number, because you can use the 2968 with channel

plan NO PLAN and enter the transmitter frequency directly in Hz.

However, when you are testing a mobile in normal trunked mode

(MCCH) you will need to set up the 2968 with a channel plan and

channel number. The TETRA signalling protocol uses the channel

number, not the frequency, when the mobile is assigned to a traf-

fic channel or control channel. Therefore the channel plan and

channel number must be correct for these procedures to work,

i.e. both the 2968 and the TETRA mobile must have the same

understanding of what the channel number means when it is con-

verted to frequencies for tuning transmitters and receivers.

The calculation and examples below are valid for the standard

channel numbering scheme defined in ETSI TS 100 392-15 v1.2.1

and required by the TIP (TTR 001-1 v3.0.13 TIPv3 Core Services).

The numbering is defined in terms of the base station transmitter

frequency:

• Identify the relevant base station (downlink) frequency,

accurate to 1 kHz or better

• The frequency should be the centre frequency of the

TETRA modulated signal

• The frequency should be an exact multiple of 25 kHz,

12.5 kHz or 6.25 kHz

• Round the frequency up or down so that it is an exact

multiple of 6.25 kHz

• Subtract an integer multiple of 100 MHz, leaving a

remainder less than 100 MHz

• The integer gives the value of the band parameter.

• Divide the remainder by 25 kHz

• The result should be in the range 0 to 3999 see note

below

• The result should be xxxx.00, xxxx.25, xxxx.50 or

xxxx.75

• Result xxxx.00: channel = xxxx, offset = 0 Hz

• Result xxxx.25: channel = xxxx, offset = +6.25 kHz

• Result xxxx.50: channel = xxxx, offset = +12.5 kHz

• Result xxxx.75: channel = xxxx+1, offset = -6.25 kHz

EExxaammppllee 11::

BS frequency = 393.612500 MHz

Subtract 300 MHz: remainder = 93.612500 MHz, band = 3

(300 MHz)

Divide by 25 kHz: result = 3744.50, channel = 3744, offset =

+12.5 kHz

Therefore channel plan = TETRA 380 MS (includes +12.5 kHz

offset), channel = 3744

EExxaammppllee 22::

BS frequency = 421.568750 MHz

Subtract 400 MHz: remainder = 21.568750 MHz, band = 4

(400 MHz)

Divide by 25 kHz: result = 862.75, channel = 862+1 = 863, off-

set = -6.25 kHz

Therefore channel plan = TETRA 410-6 MS (includes -6.25 kHz

offset), channel = 0863

EExxaammppllee 33::

BS frequency = 867.425000 MHz

Subtract 800 MHz: remainder = 67.425000 MHz, band = 8

(800 MHz)

Divide by 25 kHz: result = 2697.00, channel = 2697, offset =

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 24

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Aeroflex 2050T SERIES Especificaciones Pagina 18

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