37 TOPA-SV-024 Test Unit  Tuneup 
 August 2004 © Tait Electronics Ltd
Rx / Tx/PTT switch
This 2-way toggle switch is used to switch between receive and transmit mode. 
■ When set to Rx, the PTT line is switched to high impedance.
■ When set to Tx/PTT, the PTT line is pulled to ground.
Speaker / Radio / Load switch
This 3-way toggle switch is used during receive audio tests to switch the audio 
to the test unit speaker (Speaker), to the radio’s internal speaker (Radio) or to 
a dummy load consisting of R1 and R2 (Load).
Note This switch does not disconnect the radio’s internal speaker on 
M8100 radios with a user interface. If the switch is set to Speaker 
or Load, this simulates an external speaker being connected in 
parallel to the radio’s internal speaker. TM9100 radios without a 
user interface do not have an internal speaker.
With all settings, a low level audio signal is available for testing through 
the SINAD port.
Tait Orca portables ■ When set to Speaker, only the speaker of the test unit is active.
■ When set to Radio, only the speaker of the Tait Orca portable is active.
■ When set to Load, no speaker is active. The audio signal is terminated in 
the test unit dummy load.
TM9100 radios with 
user interface
■ When set to Speaker, the speakers of the test unit and the TM9100 are 
both active. The speaker of the TM9100 cannot be disconnected.
■ When set to Radio, only the speaker of the TM9100 is active.
■ When set to Load, the TM9100 speaker remains active.