industry
Far left: steel coil, one of the plant’s principal products
Left: the coal yard, one of the large
outdoor areas on the Tubarão site. For safety, as well
as efficient running of the plant, radio communication is essential
As for radio channels for the new network, the team could
have migrated to 400MHz, the band most widely supported by TETRA terminal manufacturers and offering the best choice of products. But because the plant already had many wireless remote controls and other systems on 400MHz, the decision was made to remain in the old 800MHz band, to avoid any danger of interference to those controls. With the system installed and operating, the plant now has
2000 Teltronic mobile and handportable radios connected and more than 400 TETRA talkgroups in operation. Tese include emergency fire and medical teams as well as working groups across the site. Among the novel service features for radio users is
telephone-style full-duplex voice communication when calling a PABX extension or a mobile phone via the gateway. Teltronic was able to help in defining the TETRA
talkgroups by studying the traffic on the analogue system. During the process of migrating the users from analogue, back-to-back radios provided a temporary bridge between the old system and the new.
Optimizing the system Tough the TETRA system immediately delivered a significant improvement in communications performance, the need for some adjustments to the system soon emerged, and the communications team has worked through these with Teltronic’s help. “We were not surprised because we had some problems with the EDACS too”, Mr Gagno commented. Perhaps the biggest change was a decision to upgrade the
traffic capacity of the system. Te radio site in the industrial area was equipped with four TETRA carriers, providing 15
voice channels plus a control channel. But because of the lesser radio traffic expected in the administrative area, the other site was installed with only two carriers – a control channel plus just seven voice channels. With experience, though, it was found that calls initiated
in the industrial area were sometimes being dropped at busy times if the users roamed across the site, because there might be no free channel available on the other base station to pick up the call. Te solution was to add two more TETRA carriers at the smaller station, making the system symmetrical. In a further step, network capacity has since been doubled to 8 + 8 carriers.
End of the beep A separate problem, solved partly by training the users, arose from a difference in the mode of operation between TETRA and the old EDACS system. Users were in the habit of pressing the push-to-talk button and waiting for a beep, but with TETRA no beep came. “Tey said, ‘Tis is not a good system, there is no beep’”, lamented Antônio Gagno. He explained: “You have two ways of trunking – by
message or by transmission. In the case of EDACS, we used transmission – so every time you pushed the PTT, you started a new conversation on another channel. With TETRA, it’s different, like MPT. So at the beginning, to make it transparent to the user, we tried to put zero seconds of retention time, so it would work like EDACS. We had to put it at two or three seconds and to train and to explain to all the users this difference.” “Tis 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.” Tree 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.
A hot steel slab emerges from the mill. Steel buildings and
machinery across the site caused radio reception difficulties which had to be solved
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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.
TE TRA TODAY Issue 6 2012
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