[aprssig] Transmit Now

[Tom Mandera]

> Date: Wed, 23 Feb 2011 09:20:17 -0500
> From: "Wes Johnston, AI4PX" <wes at ai4px.com>
> Subject: [aprssig] Transmit now pin
> Message-ID:
> 	<AANLkTimzFGjp5O8FwqHj=J5qU3zw+gLXe7C_z+-uaEoK at mail.gmail.com>
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>
> One of our locals is complaining about the muting effect of his tracker.
> His radio is being desensed by the aprs tx on the 2nd radio.  So I'm
> thinking of alternatives for him.
>
> 2)Use the tracker on a separate radio but run the PTT line from the mic to
> the "tx now" pin on the tracker.  This way when he unkeys the tracker will
> tx a position off the 2nd radio in the car.  Maybe an opto-isolator to
> keep
> things playing nicely.
>
> Anyone fooled with any of this?  I'll probably set up a tracker to test
> all
> of this, but if anyone's done it I'd love to hear about it.

Wes - how about the "Carrier Detect" pin?

Draw audio from the "voice" rig and use the audio to raise the CD pin on
the tracker.  This would disable the tracker from transmitting until
carrier is lost.

You would need to use an external speaker on the voice rig, and some
circuit to translate "any" audio on the line into the necessary CD signal
- perhaps some of the recent "No key PSK" interfaces would provide some
insight.  There was one in this month (or last) QST.

Your timing is great - I just put the second VHF/UHF antenna in the roof
of my Scout and am preparing to mount the second radio for APRS.  I've
been going back and forth on putting a D700/D710 in, but with the amount
of dust the FT-2800 is currently covered in, it would be better if I could
avoid radios with fans.  I could use a circuit just like the one you'll
need.

-Tom
KE7VUX