Product Manual

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20-62 VHF & UHF TRANSMITTER
Product Manual
Sea Air and Land Communications Ltd, 10 Vanadium Place, Addington, Christchurch 8024, New Zealand June 2020
Over-Temperature Cutout
Overview
If the transmitter operates for extended periods in a hot environment, a protective thermal cutout
may operate to reduce the output power to a safe level. It will reset when the unit temperature
has fallen below 75 degrees Celsius.
Operation
Prior to the transmitter powering up, the NTC on-board resistor is checked. If the transmitter is
above 75 degrees Celsius the maximum power level is limited to 1 watt.
In addition to the pre-transmit power check, the temperature is checked once every second. If
the transmitter is already operating and the temperature is above 75 degrees Celsius then the
power will be reduced to 1 Watt (if set above 1 watt). The full power capability of the 20-62 will
not be restored until the transmitter has powered down, and the temperature has reduced
below 75 degrees Celsius again.
If the 20-62 is being externally modulated and the temperature exceeds 85 degrees Celsius, the
20-62 is considered to be critically hot, and powers down.
When critically hot, no further messages queued for processing or transmission will be allowed
until the 20-62 has reduced in temperature below 85 degrees Celsius. In addition, attempts to
enable the 20-62 transmitter using the external PTT line will have no effect until below 85 degrees
Celsius.
If the transmitter has been controlled via the external PTT line, and for some reason the 20-62 has
become critically hot, then the 20-62 will not transmit again until the unit has dropped below 70
degrees Celsius.
Notification When Over-Temperature
When the 20-62 is above 75 degrees, but not critically hot, there is no serial or visual indication
that the 20-62 has reduced in power.
When the 20-62 is critically hot, the serial message “ER7 OVERTEMP” is sent out both serial ports,
and the red LED flashes, but does not continue to flash.
There is no messaging when the 20-62 temperature has reduced again. However, when a
message is sent for transmission, there will be a suitable response to indicate if the queued
message has been transmitted.