TM 11-5820-890-20-1
1.11.
TRANSMIT SIGNAL PATH. Continued
f.
RF Foward Power. The RT has four RF power settings L, M, HI, and PA. See Equipment Data for
power levels. When the AS-3683 manpack antenna is used with the RT, an internal impedance matching
network matches the antenna impedance to that of the RT. The vehicular antenna and the RT have
impedance matching networks to match the 50 ohm RF cable.
g
RF Reverse Power Protection. No damage shall occur when transmitting into a VSWR between 1 and
infinity. The RT will not be harmed if it is keyed without an antenna connected. When the VSWR circuit
detects a VSWR greater than 5:1, it interrupts (disables) the handset sidetone.
1.12.
FREQUENCY HOPPING OPERATION.
a.
General. The RT-1523 series contains circuitry which provides encryption and decryption for
Communication Security (COMSEC). Transmission security is provided by frequency hopping, with the
frequency determined by the variables, including time, which are loaded into the RT When all data is
loaded into the RT, the radio can change frequencies (HOP) more than one hundred times a second.
b.
Frequency Hopping Variables. The process of frequency hopping requires four data elements or
variables. They are: (1) a hopset, which is a group of frequencies (30 to 87.975 MHz) that the radio uses;
(2) a TRANSEC (TSK) key, which is used in selecting the frequency hopping sequence; (3) a NET ID, a
three digit number from 000 to 999 that fixes the hopping start point; and (4) sync time, which must be
within +/- 4 seconds of each other.
C.
RF Clrcuitry. The RT uses the same RF circuits for both Single Channel (SC), and Frequency Hopping
(FH). In the FH mode, the intelligence is converted into digital data of 16 kbps. The digital data is then
distributed across the frequencies of the hopset. The distributed signal is then processed by the RF
amplifiers and spread over a number of RF frequencies prior to being transmitted. The receiver, however,
must be able to track with the transmitter in order to decipher the digital message of the frequency
hopping transmitter. The transmitter provides the receiver with certain signals that enable the receiver
and transmitter to synchronize with each other. With the receiver and transmitter in sync, the receiver
converts the message back to either voice or data.
1.13.
TIME MANAGEMENT.
a.
General. Before the RT-1523 series radio can operate in a frequency hopping net, it must have sync
time entered. All RTs in a net must have the same net ID, TRANSEC key, hopset, and FH sync time
within +/- 4 seconds in order to communicate with each other. If the sync times are different, the RTs
cannot communicate in FH mode.
b.
Timing Restrictions. There are different operating time restrictions for the RT. The time restrictions
apply to different operating modes as listed below.
Active in-net usage
+ 4 seconds
Passive late net entry
T 1 minute
Use of ERF capability
T 1 hour (RT- 1523)
100 days (RT- 1523A/15238/15236/1523D and 1523E)
C.
Base FH Sync Time. If the FH sync time is entered with the front panel keyboard, all clocks of the RT
are set to the base FH sync time entered through the keyboard. If the FH sync time is entered by ERF,
the following will occur:
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