[Elecraft] Off Topic -- Yagi Antenna SWR measurement ?

[Phil Hystad]

I know this is OT but there are so many knowledgable people on this reflector
that I can't pass it up.

A friend has a Yagi antenna (HF tri-bander) that he wants to measure the SWR
before he raises the antenna up on the tower.

Question:  is this accurate or does the proximity of ground (maybe two feet high)
so strongly affect the SWR reading that the measurement is not accurate.

73, phil, K7PEH