User's Manual

HF NETWORKS
ENTRIES FOR AN HF NETWORK
ENVOY™ TRANSCEIVER REFERENCE MANUAL 135
This example assumes that the transceiver at each station is set up similarly. The
length of preamble sent at the beginning of a call is calculated from the information
from the scan tables associated with the HF network. If the communicating systems
are set up identically for automatic channel dwell time and number of channels being
scanned for each HF network, then this information provides the exact duration of
preamble required.
In Figure 42 above, the time taken to cycle once through all of the scanned channels is:
(5 × 125) + (3 × 250) = 1375 msec (assuming that scanning for voice and data are not
enabled)
20% of the raw time is added as a buffer, so the preamble time becomes 1.2 × 1375 =
1650 msec
In this example, the preamble sent from the calling transceiver must be 1650 msec. If
you set the Preamble Length entry to Auto, the transceiver sums the total channel
dwell time for each scan table associated with the HF network.
If you are calling a station that uses identical HF network information, the preamble
of the calling station matches the detection requirements of the called station.
Related links:
Preamble on page 134
Channel dwell time on page 122
Send preamble
You can set up the HF network to always send preamble, or only when it is scanning.
Therefore, if you are operating in an HF radio communication network that requires
stations to not be scanning, you can reduce network traffic by selecting Only when
scanning.
Related links:
Preamble on page 134
Sounding interval
The Sounding Interval entry applies to ALE/CALM HF networks only. The
sounding interval is the time between automatic sounding signals that the transceiver
sends to other stations to assess the quality of the channels in the HF network.
The recommended value is 5 hours. The longer the value, the longer the transceiver
takes to update its channel quality information. If the value is set to 5 hours, the
transceiver takes 5 days to completely update channel quality information. Longer
sounding intervals decrease the interruptions on channels allocated to this HF network
via a scan table.
NOTE: Link quality information is also updated each time a call is made or
received.