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NOTE 8. TOD key  No function in SC.
When replacing the AN/ARC-186 radio with 9. SQL key  Toggles squelch between on and
an AN/ARC-201 FM radio, a CV-3885 Data off.
Rate Adapter must also be installed.
3-17. AN/ARC-201 SINCGARS SINGLE
CHANNEL OPERATION.
Operation of the AN/ARC-201 VHF FM radio is
controlled from the FM-1  FM-2 Radio Control page
(Fig. 3-10). The area at the top of the Control page
displays radio status information on four lines. The first
line provides the title of the page FM-1 or FM-2. The
second line indicates whether the radio is in RETRANS
or blank. The third line displays the channel number
and associated frequency. The fourth line displays the
six character identifier for that channel.
NOTE
After power is applied to the SINCGARS
AN/ARC-201 radio, line address keys are
unusable for approximately 1 minute while
the radio does self-test and frequency
preset initiation.
1. COMM key (or DSPL SEL switch)  Press.
COMM page (fig. 3-7) displays.
PULL
MAN
PULL
BKUP
BRT
C
ONT
VSD HSD MMS COMM
FM-1
RETRAN
6 040.750
ATIS
EMER T/R
SC FH
PWR LO
KYBD
TOD 21 23:59
406075-1414-1
J0546
ON SQL
+10 OSET
2. L-1/L-5  Press to select FM-1 or FM-2 and Figure 3-10. FM-1  FM-2 Radio Control Page (SC
frequency list (fig. 3-8). Mode)
3-19
TM 1-1520-248-10
10. OSET key  Used to select a frequency c. A hopset (HSET) to identify the frequencies
offset for current preset or manual frequency. used by the net. Hopset i s received/
OSET may be required when dissimilar radio transmitted with the ERF.
sets are being used and local interference is
encountered. OSET is not normally used and d. Lockout set (LSET), if required, to identify
should be set to 0. Options available are 0, frequencies that will not be used by any
+5, -5, +10, -10. Offsets are in kHz. For nets. Received/transmitted with the ERF.
example, 50.400 would become 50.405 if +5
were selected.
e. A net identification (ID) to determine a start
point for frequency hopping (e.g., 310 or
3-18. AN/ARC-201 SINCGARS FREQUENCY 350). Received/transmitted with the ERF.
HOPPING OPERATION.
2. In the FH mode the audio signal is converted
into a digital data stream prior to being
1. The frequency hopping (FH) mode is an
transmitted. The data stream is interleaved
electronic counter-countermeasure (ECCM)
(transmitted out of sequence). This spreads
technique used to counter enemy jamming
the signal over several frequency hops and
and direction finding equipment. The receiver
reduces the degradation that could be caused
transmitter (RT) changes frequency more
by jamming. At the receive end, the process
than 100 times per second. It can hop among
is reversed to recover the original audio.
2320 individual frequencies. Both the
When the RT is first keyed, a synchronizing
transmitting and receiving FH radio jump in
signal is transmitted prior to the interleaved
an identical sequence. In order to function in
message. When the receiving RT detects the
the FH mode the RT needs the following
signal, it decodes it and adjusts its timing
data:
circuitry with the transmitting RT. When the
transmitting RT is unkeyed, an end of
a. Transmission Security (TSEC) variable. This message code is sent twice. This tells the
v a r i a b l e d e t e r m i n e s s e q u e n c e o f receiving RT to return to its passive receive
frequencies. This variable can only be or idle mode. While in this idle or passive
loaded via the fill connector on the radio set mode the RT searches for the synchronizing
in the aft electrical compartment and will not signal at the beginning of a transmission.
be transmitted with the Electronic Remote When a n RT r e c e i v e s a message, i t
Fill (ERF). automatically adjusts its clock toward the
transmitting RT clock. This adjustment can be
b. FH s y n c t i m e , t o s y n c h r o n i z e t h e a maximum of one-half second for each
transmitting and receiving radios. This time received message. The normal search
is established by the master net control procedure allows the receiving RT clock to be
station and is received with the ERF. When off by plus or minus 4 seconds and still be in
aircraft power is turned off, the RT clock is sync. When the late entry mode is selected,
kept running for 24 hours. After 24 hours, the search procedure is changed to permit a
the clock is turned off to preserve the plus or minus 59 second difference. Late
holding battery life. All fill data is retained entry sync data is included with the regular
　
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