EMS Technologies Canada Ltd. HSD-400 Manuale Utente

(4) WOW Pin Wiring

WOW wiring is optional for system operation.

The WOW1 and WOW2 pins are either left open circuit or connected to the airframe 
DC ground. The WOW Program Select (PGM) pin is either left open circuit or 
connected to the Forward Address Common. The three ground states, defined for 
any pin are:

•

OPN: Open circuit

•

AFG: Airframe DC Ground

•

FAC: FWD Address Common (TP7K)

Resolve any conflict between WOW1 and WOW2 by assuming the aircraft is “in-air.” 
The interpretation of the state of the WOW1 and WOW2 pins is defined by the state 
of the WOW program select pin. Refer to Table 3-4 for details.

Use of the WOW discretes enable the HSD-400 terminal to determine whether or not 
the aircraft is airborne. However, in Stand-Alone Mode installations, the HSD-400 
terminal receives speed information for Doppler correction via the INS. This makes 
the WOW wiring redundant and optional for most installations. 

The functionality of the WOW discretes was expanded to include the ability to inhibit 
RF transmission when the aircraft is on the ground. Please note that WOW 
functionality is disabled by default and must be enabled in EEPROM. If WOW wiring 
is not wired, normal maintenance activities should be prohibited when speed or 
Doppler readings are greater than zero to avoid RF exposure. Follow normal safety 
procedures and disable the SATCOM system before performing antenna 
maintenance.

The functionality will be further enhanced with the inclusion of a Transmit Disable 
discrete in a planned future software upgrade.

DLNA Gain

53

60

DLNA Noise Figure

1.5

1.8

DLNA-HSD-400 (Rx) Loss

6

25

HSD-400-Antenna (Tx) Loss

1

2.5

DLNA Insertion Loss (Tx to 

Antenna Port)

–

0.8

WOW1

WOW2

PGM

TP3G

TP3K

TP3J

AFG

AFG

FAC

In-air

OPN

AFG

FAC

Not valid - Default in-air