[Milsurplus] What is it?

[AKLDGUY .]

I agree that normal-off is an undesirable condition, since the
monitoring site wouldn't know whether the situation was normal or
whether the transmitter/receiver/indicator had failed. More likely,
the transmitter ran continuously, transmitting "situation normal"
state and that would be indicated by perhaps a green lamp.

This brings to mind a telecommunications engineering design lapse that
actually occurred here. The power failed at a remote microwave station
and back in the city we got the 'power failed' and 'diesel generator
running' alarms. We knew there was nothing to worry about in the short
term as the generator was capable of running the site for something
like 24 hours.

Sure enough, both alarm conditions shut off after a couple of hours
and we assumed that the electricity company had restored power. About
30 hours later, all data going through the site was lost - it was
dead. Techs were dispatched and it was eventually found that the
engineers had never built in a way to switch the site back to mains
power after restoration. The diesel generator had run until fuel was
exhausted, and the site had then continued on battery power until the
batteries died too. The fact that the diesel had stopped was not
relayed, because it was masked by the mains power reset.

73 de Neil ZL1ANM