Wes,
What you have posted is very interesting and is not spewing out alot of
stuff
regarding isentropic gain etc that is really not relevent to an actual
testing range.
Rather than deflect away from Reg's needs may I go back to the "compared to
a dipole"
statement which Richard keeps brushing off. If the gains are different then
the
angle for max radiation is different and if you do not take this into
account by searching
for the individual point of maximum gain position then the the measurements
are in total error.
To put antennas at the same height and then measuring at the same stationary
point for receive,
switching back and forth
is not a true comparison because of the different elevation angles. If one
was to compare a long yagi
to a dipole ando make it a true comparison measurement one must surely take
into account the two degree
or so difference when positioning the listening posts and not relying on a
single
listening position which to me appears to be a NO No .
Richards response to the "error" question totally ignored TOA saying they
are usually
the same . He also ignored what he considered as an "equal" height for the
curtain,
i.e the top,bottom or the center line of the curtain array which alone would
introduce
error with respect to comparible measurement. If Richard was pointing out
that his was a typical
professional method of measurement then I would view his statement in
complete disbelief.
Your posting, thankyou, confirms my thinking in that the use of a dipole
only confirms the reliability
of the set up used and that is the end of it with respect to measurement of
a competing antenna
where I suspect a pro lab would identify the particular resulting elevation
measurement.
If the last sentence is in error I would apreciate a correction
Regards
Art


"Wes Stewart" wrote in message
...
On Sun, 24 Apr 2005 05:44:34 +0000 (UTC), "Reg Edwards"
wrote:

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.

As stated by Ian, there's no simple answer. The bane of antenna
testing is reflections reflections reflections.

It may come as a surprise to our correspondent who likes to disparage
"gurus" that "standard-gain" antennas are widely used as reference
standards. To head off the question of how the standard gain is
determined, that is done by testing three "identical" antennas in
pairs; each one against the other two, with one the source and the
other the receiver. A bit of algebra and you have the gain of each
one individually.

http://www.mi-technologies.com/literature/a00-044.pdf

The foregoing paper might help answer Reg's question about achievable
accuracy.

While not addressing hf and vhf measurements, some of the following
might be of interest.

Indoor measurements are usually conducted in anechoic chambers where
the shape is often tapered to control reflections and the walls are
covered in absorber material. A chamber will have a "quiet zone"
where the reflections are specified to be X db down. Very often the
antennas under test are being characterized for side lobe levels or in
the case of monopulse radar, the null depth of the difference
pattern(s). If you're trying to measure a 60 dB null, it doesn't pay
to have a quiet zone of -40 dB.

These measurements also require an amplitude and phase front that
mimics a source at infinite distance. This used to require huge
chambers, often hundreds of feet long. A new way to accomplish this
is to "fold" the range by using specially shaped reflectors to flatten
the amplitude/phase across the test aperature. This has the added
benefit of shorter cables between sources, DUT and measurement
receiver. At X and K band, cable loss can be a killer. Likewise
moving cables around and even temperature changes can affect the
measurments.

I have used such a range to measure antennas from L to Ka band.

Outdoor ranges often "feature" the ground reflection, since it is
difficult to eliminate it physically. This is particularly true at
hf/vhf. I have used a technique that utilized the time-domain
capability of a modern network analyzer (HP-8510) to identify the
reflection and then place absorber material to attenuate it.
Similarly, a frequency-domain measurement, that includes ground
reflection, can be transformed to the time domain where the reflection
is gated out and then transformed back to the frequency domain for
"reflection free" analysis.

See also:

http://www.lehman-inc.com/pdf/mag2.pdf