The importance of setting  the TNC's deviation level using XMITL command

Winlink Express calls it - deviation level adjustment XMITL which is set from within either of the Packet Winlink or P2P under the setting tab once you know the correct level.

Two of the biggest mistakes I have seen is leaving the TNC XMITL level default or by those that think they can set the deviation by ear.

This really needs to be done with the use of a Communication Service Monitor test set.

Even if setup in the past, over the years the Radio's, TNC's, Software have been changed out or the TNC have been reset or when changing the internal backup battery.

Explanation of XMITL
XMITL = Transmit audio level adjustment that equates the level of deviation required.

Transmit Level is normally measured in mV (millivolts) and set to required deviation level of the transmitted audio.
The Kantronics KPC3 (not the Plus version) used a physical potentiometer.
Kantronics KPC3+ (Plus)  used soft pots therefore the XMIL command = the deviation of the radio output.

Kantonics KPC3+ output drive level (transmit audio voltage, TXA) from the KPC-3 Plus to your radio is adjusted digitally now and is set with the TNC command called XMITL.
The default from Kantronics is XMITL = 100 and they had to set it to something and that is a middle of the road setting.
The Kantronics XMITL will accept anywhere from from 0-502
Winlink Express whill accept anything between 30 - 3000 (I haven't seen any Radio/TNC above 300 yet).
XMITL number needs to be set for the correct level to achieve between  2.75 - 3.0 kHz of deviation for our area due to the Mountains and Water which can cause multipath and yours may vary.

Note: The TNC & Radio then becomes a matched pair and if either is changed out, then the process this will need to be done again. A label on the TNC with the radio serial number and XMITL should be applied once it has been setup is a good way to keep track of the matched pair

In the streen shot is where the soft pot is ajusted in Winlink Express
It states - "Disable  Xmit Level Adjust"  which is grayed out if checked and the box to the right is where you enter the XMITL (Transmit level adjustment or Deviation softpot value)

This setting was using a Yaesu FTM-400D/DR and a CT167 cable to a KPC3+ ver. 9.1