The radio did transmit perfectly but the red LED on the intercom did not
work, probably because of the 0.6V drop across the diode.
I have decided to fit a relay and do away with the diode.
regards,
Mike
----- Original Message -----
From: "Nigel Charles" <nigelcharles@tiscali.co.uk>
Subject: Re: Europa-List: Navaid Autopilot.
<nigelcharles@tiscali.co.uk>
>
> >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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