Tue May 03, 2016 8:42 pm
#1452782
I have an SPA-400 intercom wired via a CP136 audio panel and had two KX155 Coms.
When I measure the Tx Key line (PTT) at the Com it is not switched to ground but varies between +5ve (not keyed) and +1.2Volts Keyed.
Whilst this satisfies the TX Key line input to the KX155, the radio I want to fit is a Funke ATR833 and this requires 0V or GND on the TX Key line and wont transmit with 1.2Volts on the PTT line.
Have any other Avionics engineers found this problem and found a solution, apart from putting a relay in, or whether infact the SPA-400 is faulty; but fault has been masked by tolerance of the KX155 to just a LOW voltage on the TX key line.
Thanks
John
When I measure the Tx Key line (PTT) at the Com it is not switched to ground but varies between +5ve (not keyed) and +1.2Volts Keyed.
Whilst this satisfies the TX Key line input to the KX155, the radio I want to fit is a Funke ATR833 and this requires 0V or GND on the TX Key line and wont transmit with 1.2Volts on the PTT line.
Have any other Avionics engineers found this problem and found a solution, apart from putting a relay in, or whether infact the SPA-400 is faulty; but fault has been masked by tolerance of the KX155 to just a LOW voltage on the TX key line.
Thanks
John
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