[aprssig] Use of 9k6 port for 1k2 packet

[Randy Love]

It has been my experience to not worry about it when going this route. If
you set the tx and rx levels to proper deviation levels, it hasn't been a
problem for me running 1k2 baud APRS on 9k6 ports.

Of course, ymmv.

Good luck es 73,
Randy
WF5X

On Sun, Apr 4, 2021, 3:01 PM Greg D <ko6th.greg at gmail.com> wrote:

> Hi folks,
>
> I expect this is a simple R + C circuit, but have no idea what values to
> use.  Any suggestions?
>
> What I'm looking to do is to use the 9k6 port on my mobile rig (an
> Alinco DR-610) for regular 1k2 packet radio.  The advantages of the 9k6
> port is that the level is unaffected by the rig's volume control, and it
> has a separate connection at the back of the rig for both the audio and
> PTT, leaving the radio's voice function intact.  I'd be using one side
> of the radio for voice and the other for packet, not at the same time,
> of course.  I did a quick "smoke test", and at least the receive side
> seems to work.  I need to wire up a PTT circuit (simple 1-transistor
> buffer) for the transmit side, but that will need to wait for a few
> minutes of spare time.  The TNC is a Raspberry Pi 3B with a USB sound
> dongle and Direwolf.  PTT is via a GPIO pin, through the buffer.
>
> The usual problem with using a regular audio connection for 9k6 packet
> is the audio response shaping (pre / post emphasis), which kills the
> higher speed operation.  I want to do the reverse.  How do I properly
> "shape" the 9k6 port's audio stream for reliable 1k2 packet operation?
> Do both transmit and receive each need shaping, or (given the success
> with receive) just transmit?  Or, neither, and just wire the ports
> directly to the USB dongle and call it close enough?
>
> Thanks,
>
> Greg  KO6TH
>
>
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