>To prevent interference with the Navaid system during radio transmission,
the installation diagram calls for an earth on pin 7 ( through the PTT
button) for the duration of the radio call. The circuit also calls for a
diode in the radio/intercom line. This diode prevents correct operation of
the PWR/XMT led on my PS intercom system.<
Presumably the diode prevents reverse current if pin 7 should have a higher
voltage than the PTT connection on the intercom/radio. I would be very
cautious about leaving it out. Are you sure you wired the diode the correct
way around. The band end of the diode should connect to the PTT and pin 7.
Mine works OK in this configuration. The voltage drop on a forward biased
diode should only be about 0.6v so should not be enough to affect the PTT
connection. If you are still having problems try transmitting with the diode
in circuit but with the pin 7 disconnected. If this doesn't cure it there is
either a problem with the diode or there is something odd about you
intercom/radio setup. The PTT connection is usually connected to ground to
get the radio to transmit. I presume this is the case with your system?
Nigel Charles
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