Common Field Mistakes
A short list of mistakes accounts for nearly every antenna-related error a GNSS user will encounter, and every one of them follows directly from the last chapter.
The most common antenna-related field errors are forgetting to add the APC offset at all, adding it twice by misunderstanding which party the software expects to handle it, selecting the wrong antenna model after a hardware swap, and mismatching the measurement method setting against how the height was actually measured.
Forgetting the Offset Entirely
Entering only the pole height to the ARP, when the software actually expected a combined total including the APC offset, produces a small, consistent vertical error equal to whatever that offset happens to be for the antenna in use, typically several centimeters. This is the single most common version of this mistake, and it produces no warning at all.
A missing APC offset behaves exactly like a small, fixed elevation bias, present in every point from that session, precise and repeatable, and easy to mistake for ordinary measurement noise rather than a specific, identifiable setup error.
Adding It Twice
The opposite mistake, entering a combined total height and then also selecting an antenna model in software that automatically adds its own offset, double-counts the correction and produces an error of the same size in the opposite direction. This happens most often when a crew's habitual entry method does not match what a new piece of software actually expects.
A visible antenna model selection in software does not tell you, by itself, whether that selection is adding an offset on top of what you entered or expecting you to have already included it. Confirming which is the case, described in the last chapter, is the only way to know for certain.
An Antenna Swap That Changed the Model
Replacing an antenna with a genuinely different model, without updating whatever setting tells the software which offset to use, silently applies the previous antenna's value to different hardware. Replacing an antenna with another unit of the exact same model carries no such risk, since the offset is a property of the model, not the individual unit.
A Measurement Method That Does Not Match the Measurement
Entering an accurate height measurement against the wrong measurement method setting, vertical, slant to a notch, or true vertical, mismeasures the antenna just as surely as an inaccurate measurement would, since the software applies its own internal conversion based on that setting.
A rover's elevations are consistently off by the same small amount, on every point collected during a session. What is worth checking first? Whether the antenna height entry matches what the software actually expects, a missing or doubled APC offset, before suspecting the correction source or reference frame.
Nearly every antenna-related field error is one of a small handful: a missing APC offset, a doubled one, an unupdated antenna selection after a swap to a different model, or a mismatched measurement method. Each produces a small, consistent, and entirely avoidable error, caught by confirming the setup explicitly rather than assuming it.
Understanding these mistakes is one thing. Building the habit that actually prevents them in the field is the next, more practical step.