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should be set to 0. Options available are 0, kept running for 24 hours. After 24 hours,
+5, -5, +10, -10. Offsets are in kHz. For the clock is turned off to preserve the
example, 50.400 would become 50.405 if +5 holding battery life. All fill data is retained
were selected. (TSEC variable, hopset, and lockout sets).
11. DATA MODE key  Pressing R-3 toggles NOTE
DATA MODE between SDM and EDM modes.
When in the SDM mode, legend consists of • Fill batteries for the AN/ARC-201D are
text DATA MODE on line 1, SDM (boxed) on located in the aft electrical compartment
line 2, and (TAC, FS) on line 3. In the EDM/ on the front of radio and are labeled HUB
PCKT mode, legend consists of DATA MODE (hold up battery). The batteries (BA 5372)
on line 1, EDM (boxed) on line 2, and text TI are the same as the KY-58 fill batteries.
on line 3. • Five C cell batteries are in the battery box
located in the aft electrical compartment.
12. DATA RATE key  Pressing R-4 cycles
through various data rates available for the • Batteries only maintain COMSEC fills and
mode selected at R-3. In SDM mode, the TOD. TSEC and HOPSET are stored in
legend consists of the following: nonvolatile memory, regardless of
whether batteries are used.
DATA RATE (line 1) c. A hopset (HSET) to identify the frequencies
XXXX (line 2) XXXX=600, 1200, 4800, used by the net. Hopset i s received/
16K, AD1, or AD2 transmitted with the ERF.
YYYYYYYYYYY (line 3) YYYYYYYYYYY=1200,
2400, 4800, 9600, or PCKT d. Lockout set (LSET), if required, to identify
frequencies that will not be used by any
nets. Received/transmitted with the ERF.
3 - 2 6 . A N / A R C - 2 0 1 D S I N C G A R S e. A net identification (ID) to determine a start
FREQUENCY HOPPING OPERATION. point for frequency hopping (e.g., 310 or
350). Received/transmitted with the ERF.
1. The frequency hopping (FH) mode is an
electronic counter-countermeasure (ECCM) 2. In the FH mode the audio signal is converted
technique used to counter enemy jamming into a digital data stream prior to being
and direction finding equipment. The receiver transmitted. The data stream is interleaved
transmitter (RT) changes frequency more (transmitted out of sequence). This spreads
than 100 times per second. It can hop among the signal over several frequency hops and
2320 individual frequencies. Both the reduces the degradation that could be caused
transmitting and receiving FH radio jump in by jamming. At the receive end, the process
an identical sequence. In order to function in is reversed to recover the original audio.
the FH mode the RT needs the following When the RT is first keyed, a synchronizing
data: signal is transmitted prior to the interleaved
3-28
TM 1-1520-248-10
message. When the receiving RT detects the FM-1  FM-2 Radio Control page (fig. 3-16). The area
signal, it decodes it and adjusts its timing at the top center of the page displays radio status
circuitry with the transmitting RT. When the information on four lines. The first line indicates which
transmitting RT is unkeyed, an end of radio, FM-1 or FM-2, is selected. The second line
message code is sent twice. This tells the indicates whether the radio is in the RETRANS mode or
receiving RT to return to its passive receive is blank. The third line displays channel number, the
or idle mode. While in this idle or passive legend NET, and the three-digit net identification. The
mode the RT searches for the synchronizing fourth line will indicate CONTROL or MEMBER as
signal at the beginning of a transmission. selected on FM-1 Radio Control page 1. NO TSEC will
When a n RT r e c e i v e s a message, i t display on this line if no TSEC variable has been
automatically adjusts its clock toward the loaded and stored.
transmitting RT clock. This adjustment can be
a maximum of one-half second for each 1. COMM key (or DSPL SEL switch)  Press.
received message. The normal search COMM page (fig. 3-7) displays.
procedure allows the receiving RT clock to be
off by plus or minus 4 seconds and still be in 2. L-1/L-5  Press to select FM-1 or FM-2 and
sync. When the late entry mode is selected, frequency list (fig. 3-8).
the search procedure is changed to permit a
plus or minus 59 second difference. Late 3. R-5  Press to select FM-1 or FM-2 Radio
entry sync data is included with the regular Control page 1 (fig. 3-16).
synchronizing signal at a maximum of once
every 30 seconds for the net. The RT also 4. SC/FH key  Press to select frequency
checks the cue frequency during passive hopping (FH).
receive for any activity. When an RF signal
with a 150 Hz squelch tone on the RF cue 5. TOD key (L-5)  Press to display the time of
　
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