[CA] [CA11] SOG not reading

[egavasm]

On my data bar that I select what is shown such as temperature, position, etc, there is a speed over ground box which does not indicate anything, 0. I am running with a E80 mfd, connecting to a gps antenna, a 4kw radar, and a DSM 300 with a B164 1000 watt transducer without a speed wheel. All functions work ie. position lat lon etc except it no longer displays a speed. My guess is that the reading comes from gps. The gps antenna reads all satellites so would the problem be in the wiring, antennas, the mfd itself, or some other place. Where would one start to look?