LDG RT-11, Manual, Page: 5 / 8

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Pin 1 : DC power input to the RT-11. The power should be regulated, and provide between 11 and
20 VDC at 250 mA. This DC power must be present whenever the tuner is in operation. Your RT-
11 features latching relays that retain the last tuned configuration on power up. However, if your
RT-11 is connected to an Icom or Alinco radio by an interface cable, the radio sends a Bypass
command to the tuner on radio power up, requiring you to execute a tuning cycle each time you
turn on your radio.
Pin 2: Tuner bypass. Momentarily grounding this pin bypasses the tuner; RF from your transmitter
or transceiver goes directly to the antenna with no matching. When the line is grounded, the 1.5
LED on the optional remote unit will be on.
Pin 3 : Tune control. When Pin 3 is momentarily grounded while RF is present, the tuning process
starts. If Pin 3 is grounded, but no RF is present, the 1.5 and Tune LED on the optional remote
control box will flash to indicate low or no power. Once the tuning cycle starts, Pin 3 should not be
held low; if Pin 3 is held low until the tuning cycle completes, another tuning cycle will immediately
start. This pin is also used in the tuner interface for Icom and Alinco radios.
Pin 4 : Semi/Auto mode control. In semiautomatic mode, the tuner will begin a tuning cycle only
when Pin 3 is momentarily grounded. In automatic mode, the tuning cycle will begin any time the
SWR exceeds 3:1 during a transmission. At power-up, the RT-11 defaults to semiautomatic mode;
you can set it to automatic mode by momentarily grounding Pin 4. The 1.5 LED on the optional
remote unit will flash slowly when the RT-11 is in semiautomatic mode and Pin 4 is grounded.
When in automatic mode, the 1.5 LED will flash fast while Pin 4 is grounded.
Even if you provide no control circuit for your RT-11, you can still use it by putting the tuner into
fully automatic mode. This is done by grounding the Auto/Semi pin during power up. The tuner is
then in Auto mode, without needing a control circuit. LDG does
not recommend this method, as it
affords the operator little control over the tuner, but it can be useful in some circumstances.
Pin 5 : Tune LED. An LED (typically red) may be placed between this pin and ground. The LED will
light while the tuner is in the tuning cycle. A Tune LED is provided on the optional remote unit.
Pin 6 : 1.5 LED. An LED (typically green) may be placed between this pin and ground. The LED
will light continuously when RF is present and the SWR is below 1.5:1. The LED will dim when RF
is present and the SWR is between 1.5 and 2.2:1. When there is no RF present, the LED is used
to indicate Bypass, Auto/Semi and Tune modes. A 1.5 LED is provided on the optional remote
unit.
Pin 7 : Radio out. This line is used in the tuner interface with Icom and Alinco radios.
Pin 8 and 9 : Grounds. These lines are used for DC input ground, ground for the input lines and
ground for the LED outputs.
Operation : Operation varies somewhat depending on the control circuitry used. Three control
options are available: custom interface cable to an Icom or Alinco radio, the optional LDG remote
unit, or user-provided control circuitry.
LDG RT-11 Remote unit: This optional remote unit will control the RT-11 through a 15 foot DB-9
cable supplied with the unit. You can extend the DB-9 cable by up to 100 feet; shielded cable
works best in a high RF environments (be sure that all wires in the extension are straight-through
(pin 1 to pin 1, pin 2 to pin 2, etc.), and not “null modem” or some other specialized configuration).
The remote unit has front panel controls for Bypass, Semi/Auto mode select and Tune, as well as
indicator LEDs for 1.5 SWR and Tune mode. Connections for the DB-9 control line to the RT-11
tuner, DC power input for the RT-11 tuner and a connection for a radio interface are on the back of
the unit. The radio interface is the same as used in the AT-11MP, and can use the MP-IC or MP-
AL cable as an alternate interface to Icom or Alinco radios.