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

Randy Love rlove31 at gmail.com
Sun Apr 4 17:29:30 EDT 2021

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,

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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