This means that the Transmitter is unable to lock on to a stable contact resistance. There are various things that can cause a varying contact resistance and they are all related to a loose electrode stake-to-ground contact.
Check for the following:
- Check for a loose electrode stake. This connection must be solid.
- Wind can cause cables to move which in turn will move the stake. Try to place electrode cables on flat ground rather than over a bush or tall grass to ensure that the cables do not move.
- Traffic. Surveys performed close to a road can experience a similar "Wind" effect as the vehicle passes near the electrode cables.