Communications Failure on SCADA

droatcap · Post by **droatcap** » Mon Oct 30, 2006 7:40 am

We are using 1225 radios for our backbone. One UHF radio here at the office and another at an elevated tank site. At the tank site the UHF is paired with a VHF in some sort of repeater. This repeater talks and listens to the various remote sites. Lately we have been getting a bad hum that disables all communications. We thougt a remote radio might be stuck in transmit so started shutting them off one by one but haven't found the culprit. The problem has been correcting itself so it has been hard to put a tech on task not knowing when it will happen or how long it will last. This morning the office radio is silent, the usual squelches requesting Scada data are gone. The MTU is still keying the radio as evidenced by the lightning bolt on the radio display flashing in sequence with the MTU 'clicks'. What would cause a radio to do the silent treatment? Antennas? Nothing on the other end? Something else?

k2hz · Post by **k2hz** » Mon Oct 30, 2006 2:20 pm

My first thought with your description of a "bad hum" is the possibility of an interfering signal at the repeater site. Scada systems are usually carrier squelch and are subject to interference from any kind of co-channel signals.

The first step would be to monitor the VHF frequency and see if your polling signal from the master is really going out to the remotes. If the remotes only respond when polled and the VHF master station is inhibited from transmitting by a carrier detected on the channel that would cause what you describe.

The next step would probably be to have someone at the repeater site when the problem is present to see what is going on.

transistor747 · Post by **transistor747** » Tue Oct 31, 2006 11:26 am

Figure out which site is running on a battery and charger, and put water in the battery.