After ascertaining that the system is worth pursuing i.e. the requirement could be satisfied with available solutions, attention is then focused on the technical aspects of the requirements. Areas of concern are whether the timings and delays inherent with certain lower cost radio telemetry modules can be accommodated, or if higher spec systems be considered. An example is a pair of remote detectors are used to determine the speed of an object passing them (based on the time taken between each detector). If fed into a simple radio telemetry module which then sends the two inputs either simultaneously or in two separate transmissions, this timing is lost and the speed itself cannot be determined. In this instance (should wire not be suited) specially designed or high speed radio telemetry devices (usually microwave) need to be employed.
It is imperative that the full technical requirement of what needs to be linked, and at what update time or speed, is to be noted here. Examples of errors made are systems comprising a total of 100 inputs spread over the various locations, each input is required to update to a host within one minute, and each transmission and acknowledgement taking one second. Don't giggle too loudly, much personal time and effort has been spent 'repairing' such badly planned systems. The obvious cure is to re-plan the update times, lowering the non-important ones to leave time for the more important signals to be updated. This is covered in a later section but it is well worth noting such blatant traps now.
Examples of errors made on serial links are assuming that two full speed links (i.e. 9600 baud), such as found between computers and PLCs or data loggers, can co-exist on the same radio channel. This problem is further intensified should there be two separate systems requiring the same radio link, an example would be an intensively busy data logging system on the same channel as a remote controlled device, the latter never getting the time to receive a command.
In brief: All requirements need to be carefully documented as well as any tests made to determine the loading on the radio channel, especially where multiple systems need to co-exist on the same channel. Note that we have not yet planned the system. This phase is only to ascertain whether the signals that require relaying can co-exist on the same channel without swamping the channel.
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