Annex G
The TRX2 Alarm System
Version 1.07k of the firmware introduces an additional feature to the transceiver, an alarm
system to provide the user with a critical warning of potentially damaging factors.
The system can provide a warning for high SWR, power amplifier over-current, and over and
under input voltages.
The thresholds for these alarms are set in the revised System Setup & Calibration mode, as
earlier described.
High SWR
The original firmware was already provided with a simple SWR alarm, triggered if it
exceeded 3.0:1, but it simply displayed this value. Now, the user can adjust the threshold at
which the alarm is given from 1.00:1 to 5.00:1 in 0.01 increments. If the SWR exceeds the
threshold then a message is displayed and a repetitive beep sounds.
The only active button when an alarm is present is the PWR button. Briefly press this to
acknowledge and cancel the alarm. Obviously, if the event is still present, then the alarm will
return. If the alarm cannot be cleared, for example, a permanent under-voltage, then press and
hold the PWR button to invoke the emergency shutdown. This will occur faster than the
regular shutdown, and no user settings will be saved to the EEPROM.
Over-Current
This alarm is triggered if the measured final amplifier’s drain current exceeds the preset
threshold. Note that as already mentioned, the current sense only applies to the power
amplifier’s output transistors. Excessive current elsewhere in the transceiver is not sensed.
Only the input fuse can protect the unit.
The usual reason for an excessive current is a high SWR, in which case this alarm is also
likely to exist. If the alarm is present, release the PTT switch or the key and acknowledge the
alarm, and investigate its cause.
I considered carefully whether to force the transmitter off in the event of either a high SWR
or high PA current, but decided that in doing this it would make matching an antenna to the
transceiver a frustrating business if the transceiver kept tripping off whilst attempting to
achieve a match when the high SWR might only persist for a short time. It is left to your
judgement as to what level to set the alarm, but 2.5A is suggested.
Over-Voltage
This alarm is only really likely to occur when operating mobile using a vehicle electrical
system. Be aware that automobile electrical systems can have supply voltages as high as
14.8V or sometimes higher, especially if the battery is old, or has a high internal resistance, or
the electrical connections are unsatisfactory. Although the transceiver can tolerate for short
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