Further investigation shows this:- (could there be a conflict with the other feeders, FR24, FA, PP and PF?)
pi@RPi3ADSB:/etc/default $ more mlat-client
# mlat-client configuration file
# This is a POSIX shell fragment.
# You can edit this file directly, or use
# "dpkg-reconfigure mlat-client"
# Start the client?
START_CLIENT="no"
# System user to run as.
RUN_AS_USER="mlat"
# User to log into the server as
SERVER_USER=""
# Logfile to log to
LOGFILE="/var/log/mlat-client.log"
# Input receiver type (dump1090, beast, radarcape_12mhz, radarcape_gps, sbs)
INPUT_TYPE="dump1090"
# Input host:port to connect to for Beast-format messages
INPUT_HOSTPORT="localhost:30005"
# Multilateration server host:port to provide data to
SERVER_HOSTPORT="mlat.mutability.co.uk:40147"
# Latitude of the receiver, in decimal degrees
LAT=""
# Longitude of the receiver, in decimal degrees
LON=""
# Altitude of the receiver, in metres
ALT=""
# List of result connections/listeners to establish.
# This should be a space-separated list of values suitable for passing to
# the --results option (see mlat-client --help for syntax)
RESULTS="basestation,listen,31003"
# Other arguments to pass to mlat-client
EXTRA_ARGS=""