“This is very common with TETRA when they switch”, commented Peter Clemons, of Teltronic. “After a little while they get used to it. But you need to explain.”

Three repeater systems have been installed to provide reliable coverage within cable tunnels, some of the many around the site (the team has been working on adjustments to gain settings and the antennas to ensure stability and avoid interference), and one more is planned for a building in the coke plant area.

Balancing up

A more complex problem was to resolve an imbalance in the transmit and receive link budgets. Because of electrical noise in some of the production areas, sometimes the signal would be submerged in noise, causing the radio to search for a receivable channel. If it did not find one, it would eventually lock up – and could be released only by switching it off and back on again.

This was dealt with through several approaches. To begin with, the omnidirectional antenna on the administration area site was replaced with a 16·5?dBi panel antenna, to beam the signal towards the production areas, improving coverage and receive sensitivity. Signals to the rear of the panel were correspondingly reduced, but this did not matter because there were no users on that side.

In addition, it was necessary to increase the receive sensitivity at the radio sites. “Engineers from Teltronic came here – three or four engineers came here – and we spent a lot of days, weeks, in fact, making some adjustments”, Mr Gagno recalled. “That’s why we changed the omni antenna to the panel antenna and we changed the sensitivity. We wanted it to be not –97?dB but –102?dB, to make it possible to talk inside the buildings.

“As you saw, we have many ferromagnetic buildings, so the coverage was not good. But now we did it, and it’s working very good.”

The use of powerful 3 watt handportables in combination with the 75 watt base station sites also helped to overcome the noise. And the lockup problem was solved through a software adjustment. “We asked Teltronic to change the way the system communicates, the handshake, and they did it. So it was no more broken, because it tries many times without going to searching state. So even if the signal does not arrive, the system retries. We could work with this level of sensitivity – it was not blocking the system. We wanted to make it transparent to the user so the user did not have to turn off the radio.”

Another improvement, devised by Teltronic, was a keyboard short-cut so that users who needed to be in touch with several talkgroups could scan them at the touch of a button, for fast access. This was a special development for ArcelorMittal.

One important provision of the agreement with Teltronic concerns servicing the radios. “We can maintain them here on our site”, said José Martins. “That makes us capable to fix stuff and keep them working. We have a laboratory here and Teltronic has a laboratory in Bahia [Brazil]. Part is done here and part is done in Bahia – and part in Spain.”

Next steps

With a plant and a radio system of such a size, there is always more work to be done. Next items on the communication team’s wish list include radio terminals which are more dust-proof (Teltronic is working on this) and improved accessories for specialized groups of radio users. “In some places they need to use a mask for gases and things like this so we have to have another way to talk”, Mr Gagno said. “We tried to use osseous [bone conduction] microphones but they were not very good for us, so we are still studying this solution.” 

Also on the agenda is the plant’s railway system. TETRA radio installations are needed in the driver’s cab for the locomotive operators, but in addition it is proposed to convert the train-monitoring system to TETRA. At present, radio transponders on the track and on the trucks are read by antennas on the locomotive and relayed via the analogue radio system to an operator, who can then view the location of each train.

This system reports a train’s position when it passes a transponder, but does not track it metre by metre. The team plans to test a GPS receiver in one locomotive to see how well it works – but because some of the tracks run only one metre apart, the GPS signal will not be precise enough to show exactly which one a train is on.

But with the change to TETRA for relaying the positional data, it will at last be possible to shut down the old analogue radio system. 

From coal to coke with TETRA