Reg propped up this tar baby and everyone's taken a punch at it.

Perhaps it is time to check in and see if you have your answer yet
Reg.

==========================================
Wes,
Not everybody has yet taken a punch at it. There are several regular
names who are missing.

All I want is a number, eg., of decibels, preferably from a standards
lab.

But it has only been been demonstrated "Measurements" is not a
"Science" - it is an "Art". Perhaps I can clarify my question.

Suppose a customer, perhaps an antenna manufacturer, walks into the
lab wheeling behind him a weird contraption (we've heard of them) and
asks for the forward and reverse gains to be determined and for a
calibration certificate to be issued.

For present purposes actual forward and reverse figures don't matter.

But for the two figures to be of value the uncertainties in the
determination should be stated on the certificate (a legal document).

What are TYPICAL uncertainties, in dB, which appear above the Head of
the Laboratory's signature.

A laboratory or ex-member should be able to put me in the right
ballpark even if it is only for one typical case. For TRUE antenna
performance measurements the best source of information is from a
standards lab. There is no incentive to overstate performance. If
discovered, exaggeration of a laboratory's capabilities results in
loss of reputation.

In the UK, Standards Laboratories were regularly monitored for
performance by the National Physical Laboratory (NPL), in effect
Government controlled. I have been out of touch for 20 years with what
happens these days.

In the 1970's I was a Government Approved Head of Laboratory. I
personally set up the lab from scratch begining with a 30 x 40 feet
empty room. All our own standards were traceable directly to the
National Measurement Standards at the NPL.

An offshoot of the lab, also under my control, was a central
calibration service for instruments used nationally by field engineers
for investigation of radio interference complaints by the general
public and other parties. Many of the instruments were of Eddystone
manufacture whose factory was in Birmingham a few miles from the
Standards Lab. In between Eddystone's works and the lab lay B'ham
University from which the very first 3000 Mhz magnetron appeared
during the WW2 air raids on the city. Just in time to defeat the
U-Boats which were sinking a 10,000 ton cargo ship every day in the
horrible Battle of the North Atlantic. More than 100,000 merchant
seamen and suicidal iron-cross submarine crews still lie sleeping in
Davy Jones' vast locker.

That's quite enough variation for one paragraph. To return to
normal -

Although we had a small screened room to calibrate RFI instruments,
the laboratory's capabilities did not include measurement of antenna
gains and losses. Hence my modern enquiry about uncertainties.

Note: Uncertainties are best considered because they arise from a
multplicity of sources. Therefore they accumulate arithmetically -
whereas accuracies do not and are more inconvenient!
----
Reg, G4FGQ. Alias Brer Rabbit or Punchinello.