User's Manual

Message Format
B-2 Transponder PT21 Messages
There is a random delay called InterMsgDelay that occurs between two consecutive messages.
This is implemented to ensure that the delay time does not repeat itself before 32 messages have
occurred.
The following is the method of evaluating the maximum transmission time for the PT21:
Number of bytes per message: TXBytes = SC + UD + GateID + Cntrl + CRC + Flag + Key
Number of bits per byte: BitsPerByte = 12 for DR4
Number of bits per message: TXBits = Sync + Start + BitsPerByte*TXBytes
Bit duration: BitLen = 1/38400
Message length: MsLen = 0.0007 +TXBit*BitLen
Intermessage constant: InterMsgUnit = (SC+UD+2+CRC+Key+Flag)*0.0003066, for DR4
Intermessage delay: InterMsgDelay = [SD +RND(0…31)]*InterMsgUnit;
(RND - random value)
Maximum number of transmitted messages: NM = IP +RC; if LT = Y
Total transmission time: TXTime = NM (MsLen +(NM-1) (InterMsgDelay)
The following tables present the maximum number of messages (NM) that can be transmitted in
five seconds, using different sets of parameters for the PT21.