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with constant monitoring of the guard receiver.
c. GUARD mode: Allows transmission and reception
on guard frequency.
d. Normal Mode: Single frequency used.
e. HQ mode: The HQ mode of operation provides
a jam resistant capability by means of a frequency hopping
technique that changes frequency many times per
second. Automatic frequency changing in an apparently
random manner provides the jam resistance of the
radio. The HQ radios permit communication in radiojamming
environments. Three elements are required
for uninterrupted, successful communication. Radios
must use the word-of-day (WOD), be time-synchronized
with each other with a time-of-day (TOD), and share a
common net.
(1) WOD. Common frequencies, hopping pattern,
and rate are determined by the operator entered
WOD. The WOD is a secret, tactical, multi-digit code
that changes daily, and is available worldwide to all HQ
users.
The WOD programs the radio with the frequency hopping
pattern and rate. The hundredths/thousandths
digits in the channel 20 WOD element program the frequency
hop rate with .00 being the slowest and .75 being
the fastest. WOD elements vary in number and are
entered by using one or more of the six preset channels
20 through 15. Channels containing WOD elements
cannot be used in the normal preset function. Transmissions
can be made in WOD channels, but they will
not be on the frequency stored in the preset channel
memory.
3-15
TM 1-1520-236-10
The WOD is initially entered into the preset memory
and then transferred to volatile memory. After transfer,
if power is lost or if channel 20 is selected when the
function switch is set to PRESET, it will be necessary
to perform another transfer from the preset memory to
volatile memory. Start with channel 20 and set to progressively
lower channels until a double beep is heard.
The radio will not function in the AJ mode if a WOD is
not in volatile memory. If the AJ mode is selected without
entering a WOD into the volatile memory, a steady
warning tone will be heard in the headset.
(2) TOD. Time synchronization is provided by
a clock inside the radio. The internal clock is turned off
when the radio is turned off.
A TOD signal must be received to reset the radio’s internal
clock when the radio is turned on. This signal
may be provided by another HQ radio or by an external
time distribution system. Improper synchronization
will prohibit proper communication. Reception of
garbled communications in the AJ mode indicates the
receiving radio and transmitting radio are not in synchronization.
In a multiple radio net, the radio receiving
all transmissions garbled is the radio that is out of
synchronization.
TOD reception can be performed in both normal and AJ
modes. The radio automatically accepts the first TOD
message after the radio is turned on and the WOD is
transferred to volatile memory. Subsequent messages
are ignored unless the T position is selected by the
A-3-2-T switch. The radio may be desynchronized by
setting the radio to the TOD transmission frequency,
setting the A-3-2-T switch to T, and requesting another
person in the common net to transmit the TOD. The radio
then accepts the next TOD update, provided the
TOD update arrives within one minute of selecting the
T position on the A-3-2-T switch.
TOD is normally received by the main or guard receiver
via a prearranged frequency from another HQ radio
which has the desired time. When the radio receives
the TOD from an external timing source, it updates/
synchronizes the radio’s internal clock with the timing
source. This allows all radios in synchronization with
the source and one another to frequency hop simultaneously
for uninterrupted communication. Any arbitrary
time may be used, but operators are encouraged
to obtain and use Universal Time Coordinated (UTC)
time. The use of UTC time will allow operators to
switch from one HQ radio net to another without retiming
their radios to arbitrary times (TODs).
3-16
If no TOD is available from another HQ radio, an emergency
start of the TOD clock can be performed using
the T position of the A-3-2-T switch and the TONE button.
Emergency startup of the TOD clock generates an
arbitrary TOD that must be transferred to other radios
using the same net. Operators using the emergency
startup method will not be able to communicate in the
AJ mode with anyone that has not received this arbitrary
TOD. The net should update to UTC time as soon
as possible so everyone entering or leaving the net will
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