Aeroflex 2050T SERIES Especificaciones descargar pdf (Pagina 8)

Level, and by two of the parameters in the 2968 SYSTEM PARA-

METERS menu, "ACCESS PARAMETER" and "MAX TX LEVEL".

The calculation is as follows:

• Take the 2968 RF GEN level, which will be in -ve dBm,

and make it +ve.

• Add the ACCESS PARAMETER, which is in -ve dBm,

range -53dBm to -23dBm.

• The result is the mobile's transmit power, subject to

some modifications.

The calculated mobile transmit power is modified by the following

conditions:

• The mobile is not allowed to transmit at a power level

higher than MAX TX LEVEL

• The mobile cannot transmit at a power level higher than

its power does, e.g. a Class 4 Mobile has a maximum

power level of PL4 +30 dBm.

• The mobile cannot transmit at a power level lower than

its minimum, i.e. PL7 i.e. 15 dBm.

• The mobile power is quantised to defined power level

steps: PL1 +45 dBm, PL2 +40 dBm, PL3 +35 dBm, PL4

+30 dBm, PL5 +25 dBm, PL6 +20 dBm, PL 7+15 dBm.

• Some mobiles belong to an 'L' power class where their

top power level is reduced by 2.5 dB, e.g. PL4L 27.5

dBm.

QQ22..22::

Why is the mobile power level approximately 5 dB too high

or too low when I have set the 2968 RF Generator Level to the

correct value for the power level required?

AA22..22::

Mobiles are permitted +/- 4 dB tolerance in measuring the

RSSI (Received Signal Strength Indication), so it is not possible to

guarantee a particular power level for a particular RF GEN level,

except when the mobile is forced to the maximum or minimum

power. If the 2968 signal generator is set at least 4 dB lower than

the calculated value for maximum mobile power, the mobile

should be using the maximum permitted power. If the 2968 sig-

nal generator is set at least 4 dB higher than the calculated value

for minimum mobile power, the mobile should be using the mini-

mum transmit power. For the intermediate power level steps, you

can experiment with different RF Generator Level settings to

achieve the required level.

QQ22..33::

Can I use the 2968 to control the mobile power directly,

as with GSM?

AA22..33::

No. TETRA mobiles do not incorporate a direct power con-

trol mechanism, therefore the 2968 cannot directly command the

mobile to a particular power level. However, some TETRA mobiles

incorporate Closed Loop Power Control (CLPC) in which they will

respond to a command to increase or decrease their power by

one or more 5 dB power level steps. The 2968 can therefore be

used first to force the mobile to minimum or maximum power

level by using normal open loop power control, then to command

the mobile to increase or decrease power from this known start-

ing point. However, most TETRA mobiles do not support CLPC.

QQ22..44::

How do I ensure a repeatable method for testing mobiles

on a particular power level?

AA22..44::

Use the MAX TX LEVEL parameter on the SYSTEM PARA-

METERS menu to limit the mobile power to the particular power

level required. Set the RF Generator Level to a low enough level

(e.g. -100 dBm) to force the mobile to transmit at the maximum

power level permitted.

If the MAX TX LEVEL is changed, a TETRA mobile that is already

registered to the test set or active in a call may not necessarily

alter its power in response to the change, since this is not a

parameter that a mobile would expect to change on a real base

station. In this case it may be necessary to clear down the current

call or even de-register and re-register the mobile to the test set

for the parameter change to take effect. However, if the mobile is

tested in T1 Test Mode using the 2968 T1 test signal, the MAX TX

LEVEL can be used to directly control the mobile's transmit power

(with RF Gen Level set to -100 dBm).

QQ22..55::

Can I test the mobile's transmitter on different frequencies?

AA22..55::

Yes. The control channel (MCCH) may have to be on a spe-

cific frequency (channel number) in order for the mobile to recog-

nise the test set and perform registration. However, during a call

set-up, the mobile should obey an instruction from the IFR 2968

to transmit and receive on any traffic channel frequency (channel

number) within the mobile's capabilities. When the mobile is idle

on the control channel (MCCH) you can set the traffic channel

(TCH) that will be used when a call is set-up. Hence you can test

the mobile's transmitter on different frequencies by clearing down

a call, changing the traffic channel number, and setting up a new

call.

QQ22..66::

Can I test the mobile's transmitter over its entire receive /

transmit frequency range?

AA22..66::

Yes, if the mobile has a flexible RF architecture that allows

this operation. For example the 'TETRA 380 MS' channel plan can

be used to test the mobile's receiver over the range 390 to 400

MHz, and the mobile's transmitter over the range 380 to 390

MHz. However, the IFR 2968 allows you to define a reverse chan-

nel plan so the mobile's receiver can be tested over the range

380 to 390 MHz and the mobile's transmitter over the range 390

to 400 MHz. Depending on the configuration of the mobile, you

may be able to perform normal registration and call set-up with a

reverse channel plan, or you may need to use T1 test mode to test

on reverse frequencies. For further details, refer to 'Annex B:

Configuring the IFR 2968 with a User Defined Channel Plan' in the

application note 'Testing TETRA mobiles with the IFR 2968'.

QQ22..77::

Why do the TETRA mobile transmitter measurements stop

after about a minute?

AA22..77::

The measurements do not stop, it is the mobile transmis-

sions that have stopped. TETRA mobiles making group calls or

simplex private calls normally incorporate an autonomous trans-

mission timer which is typically one minute in duration, so that the

mobile stops transmitting even if the user is still holding the PTT

pressed. TETRA mobiles do not normally incorporate a transmis-

sion timer when making duplex private calls or phone calls, hence

you should always set up a duplex call where possible (e.g. a

phone call) when you want to examine transmitter measurements

in detail. This also has the advantage of not requiring you to hold

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