Richard Clark says -
Hi Reg,
I thought Wes' link was quite specific to the matter:
=====================================

Hi Richard,
I originally wrote -

"Does anyone have typical examples of measurement uncertainties
claimed
by antenna testing stations? Answers in decibels please."

The two links to papers, kindly found by Wes, are both devoted to
microwave horns and dishes. Very interesting and directly related to
the subject.

But in anticipation of the sort of replies I would receive, and in
fact did receive, I specifically asked -

"A reply from a testing station, at HF or VHF, would be specially
appreciated."

It appears that at microwaves a worst-case uncertainty of 0.2 dB, that
is a range of nearly half dB, is achievable in the National Physical
Laboratory at Teddington on Thames, London. Which is a little hard for
an Old Timer like me to believe. But at HF and VHF, at which amateurs
are mostly interested, the uncertainty on a typical open-air range is
sure to be greater. If only because great accuracy of rocket
technology at the lower frequencies is not needed.

It nearly always occurs that technical enquries at LF and HF get lost
in the elevated mysteries of microwaves, circulators and
scattering-parameters.

I am unfamiliar with precision antenna test and measurement methods. I
don't particularly wish to know. But if you, as an employee of a
reputable laboratory, were given the job of determining the forward
and reverse gains of fractal or other weird antennas, at 7 MHz and
144 MHz, what uncertainties would you state? I'd believe you.
----
Reg, G4FGQ.