SV-XPNDR-261 Transponder Installation and Configuration
12-10 SkyView HDX System Installation Manual - Revision E
• Connect the SV-XPNDR-261 RX wire (pin 5) to the SkyView serial TX of your
choosing. If you have multiple displays, the SV-XPNDR-261’s RX wire must be
connected to a serial TX wire on each display.
• Record the SkyView serial port that you have chosen on each display as you
will need to configure it later for use with the SV-XPNDR-261.
12.2.5 Mutual Suppression (Pin 18) (optional)
Mutual Suppression allows two (2) or more transmitters on adjacent frequencies to inhibit
the other transmitters when one (1) is active to limit the interference effects. It is commonly
used between transponders and DME systems, and between transponders and collision
avoidance systems. Most installations will not make use of this feature, since most
SkyView-equipped aircraft have only one (1) transponder and often do not have DME
equipment or other active traffic system that interrogate other aircraft.
The Mutual Suppression pin, Pin 18, is an ARINC compatible suppression bus interface,
which acts as both an input and an output. The SV-XPNDR-261 will assert this signal
when it is transmitting, and can be suppressed by other equipment that asserts the signal.
The SV-XPNDR-261 will drive approximately twenty-four (24) Volts on the output
(independently of supply voltage), and will treat the input as active whenever the bus has
greater than ten (10) Volts.
If you are using the Mutual Suppression feature, simply connect all the Mutual
Suppression wires from devices that use them together.
12.2.6 Ident Switch Input (Pin 20) (optional)
SkyView has an IDENT button in its TRANSPONDER menu that is normally used to ident
when requested by ATC. However, the ident switch input allows the IDENT function to be
selected using a remote switch. The input is active low, and will be asserted when the
voltage to ground is pulled below approximately four (4) Volts. Therefore, a momentary
switch to ground should be installed on this output if a remote ident switch is desired.
12.2.7 Squat Switch Input (Pin 19) (optional)
In a SkyView system, a Squat Switch is not required because SkyView can automatically
detect whether ALT or GND mode is appropriate, and switch modes as necessary. Thus,
the Squat Switch Input should be left unconnected. See the AUTO ALT/GND setting in
the SV-XPNDR-261 Settings section of later in this section.
The Squat switch input allows the SV-XPNDR-261 to automatically switch between
Airborne and Ground modes, and affects both the Mode S reply behavior and the ADS-B
reporting behavior. The input will be asserted when the voltage to ground is pulled below
approximately 4 Volts. The logical sense of the input can be programmed to be either
active low or active high in the SkyView Setup Menu.
If connected, this must be a mechanical switch that accurately reflects the aircraft’s on-
ground status. Mode-S certification requirements state that this cannot be a simple
airspeed switch.
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