Reply Coding by Category

case oi' normal operation (a above), the

u s e d i n c o m m u n i c a t i o n systems. The

MARK X IFF challenges to sif equipped

m o d e s are identified as follows:

t r a n s p o n d e r sets consist of pulse pairs

(1) Mode 1, IFF.

t h a t represent modes 1, 2, and 3, re-

(2) Mode 2, personal identification.

s p e c t i v e l y . The transponder set reply is

(3) Mode 3, flight leader identification.

a coded pulse train with a number of se-

b. Replies. Transmitted replies consist

lectable codes for each reply mode.

o f bursts of rf pulses which have been

c. Civil Reply Codes. C i v i l i n t e r r o g a -

a r r a n g e d with specific characteristics in

t i o n s , which also consist of pulse pairs

t i m e and position. The type of reply is

that represent modes 1, 2, and 3, provide

determined by the interrogation mode and

t h e necessary overlap between civil and

the operator code control selection. Spe-

IFF systems for compatibility. Replies in

cialized replies are available to the oper-

c i v i l function setting are identical with

a t o r for identification of position (i/p)

those in modified function setting ( b

and emergency operations as required by

a b o v e ) , except for the civil i/p reply ( d

t a c t i c a l situations. Mode 1 provides 32

below).

code combinations; mode 2 provides 4,096

d . Identification af Position Reply Code.

code combinations; and mode 3 provides

I/p replies can be made to any of the above

64 code combinations. The combination and

r e p l y codes (modes 1, 2, and 3). These

separation of pulses form predetermined

codes consist of repeated type replies. The

coded reply trains which are received by

c i v i l i/p reply train is not repeated but

the ground-based IFF radar interrogator

will be present for each interrogation re-

station. The ground equipment uses a go-

c e i v e d . All i/p functions are sustained

no-go decoder system to make sure the

for 30 seconds +20 -15.

r e c e i v e d coded reply train is according

e. Emergency

With

the

to tactical orders.

Reply

Code.

e m e r g e n c y function and normal function

16. Reply Coding by Category

selection, the reply consists of our pulses.

In the modified or civil function, the emer-

a. Normal Operation. I n a c o n v e n t i o n a l

gency reply to mode 1 and mode 3 inter-

Mark X IFF system, the transponder set

rogations will be the selected reply code

is challenged by pulse pairs that represent

displayed four times at the ground-based

modes 1, 2, and 3. The transponder set,

IFF radar interrogation station for each

operating in the normal category replies

i n t e r r o g a t i o n . T h e mode 2 reply in the

with a code of one (modes 1 and 3), two

(mode 2), or four (emergency) pulses.

m o d i f i e d or civil function will be the

normal mode 2 reply.

b. Modified (Sif) Reply Codes. As in the