Worth Data 7000 manual Is radio traffic contention likely?, Relay Installation

At this point, the RF Terminal puts out the “who can hear me” message. The RELAY n CANNOT BE HEARD message usually indicates a cabling problem and should be checked out immediately.

Sometimes a Relay gets a response from the Base Station that is partial data or garbage. The Terminal retransmits its data since it has not received a new prompt. If this occurs ten times, the RF Terminal broadcasts, “who can hear me”. At this point the Relay is still functioning and answers the RF Terminal’s call. Should the Relay respond to the RF Terminal first, the whole sequence starts again. If the Relay again gets “garbage” messages from the Base and the Terminal re-transmits 10 times, then the Relay concludes that there is something wrong and broadcasts the RELAY CANNOT BE HEARD message. This situation indicates that you may have an electrical “noise” problem – check your cabling as well as any electrical equipment that is in the area.

Determining coverage areas for Base Stations and Relays

As we said before, it is almost impossible to predict the effective RF communications range in a given environment. The typical area of coverage is a 3,000 – 10,000 ft. radius.

After a Site Test, if you have determined that you will need to add Relays to cover the area you want to operate in, you will need to determine where to place

your Relay in relation to your Base Station. To effectively cover an area, there must be overlap between the area covered by the Base Station and the area covered by the Relay. The example on the right shows what can happen with no area overlap:

	Keep in mind that the maximum length of wire that can
run	between a Base and a Relay or from Relay to Relay is
	4000 feet. In most cases the range of the LT7001 to the
	Base will exceed this amount unless you are operating in a
	very challenging environment.
As	you can see, the only area adequately covered is in a path
	where the two circles touch. The “dead space” is
	completely without coverage. Alternatively, locating the

Base Station and Relay as shown below results in better coverage:

To Site Survey a Relay, all other Relays and Base Stations must be turned off. This is the only way to know for sure which Relay is responding. Alternatively, perform the Relays’ test out of range of the other Relays and Base Stations.

Relay Installation

Relay Stations are connected to the Base by twisted-pair wire. See Appendix B: Adding Relays for the pin outs and a testing plan.

Is radio traffic contention likely?

The radio traffic time is about 30ms per transaction. Radio time is not going to be a gating factor, even with more terminals than the allowed 64 maximum.