"Reg Edwards" wrote in message
...
All electrical calibration and testing laboratories issue tables of
claimed accuracies of measurements. Measurement uncertainties stated
on calibration certificates are legally binding. All stated
measurement results must be traceable to International Standards or a
laboratory or testing station loses its status.

Consequently there is no incentive for a laboratory to overstate its
capabilities in its sales literature. Indeed, it is dangerous,
illegal even!

Naturally, laboratories can differ widely, one from another.

It would be interesting to compare laboratory uncertainties with
performance figures claimed by antenna manufacturers. Or anyone else.

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

A reply from a testing station, at HF or VHF, would be specially
appreciated.
----
Reg, G4FGQ

Interesting topic Reg. I have always been concerned with uncertainties
involved in antenna measurements. ATR antennas do not always provide the
source for calibration, but assume it could be ANSI/IEEE Std 149-1979.
ETS-Lingren quotes, for their conical log spiral, model 3102 antenna factor
uncertainty as SAE, ARP 958 1M (With which I am not familiar). The antenna
factor uncertainty is specified as +/- 0.8dB from 1 - 10 GHz. More data,
including other conical log spirals, biconicals etc. is available on
ETS-Lingren's web site at www.ets-lingren.com if anybody is interested.

One company I worked for was making measurements in a 3 meter shielded ATR.
Their distance measurements from the source were measured from the support
pole of a conical log spiral, when it should have been measured from the
tip. With the 3102 antenna this introduced a 3 dB error. Radiated spurious
limits quoted in V/m were also assumed to be peak, but not specified. Some
research indicated that these limits are in fact RMS -- another 3dB error!
When used for linear field measurements the conical log spiral gain is 3 dB
below that for circular polarization. Conical log spirals are calibrated
with a circularly polarized signals.

Agilents 11940A has an antenna factor uncertainty of +/- 2dB from 30 MHz to
1 GHz, and is calibrated in the far field, for near field measurements.
ETS-Lingren's antennas are all calibrated at 1m irrespective of frequency.

When questioned about accuracies of measurements people usually say "This is
the way we have always done it". I have very little experience with HF
outdoor measurements, but have heard of sites using high wooden towers to
minimize ground reflection effects. A helicopter is required to plot the
field strength. Very few EMC antenna manufacturers seem concerned with low
frequency far-field measurements. Siemens was about the only company I
could find for such measurements.

Regards,

Frank (VE6CB)