On Tue, 26 Apr 2005 19:59:59 +0000 (UTC), "Reg Edwards"
wrote:

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.

Hi Reg,

I thought Wes' link was quite specific to the matter:
Measurement Mismatch Correction Error 0.04
Noise Power of Power Sensor 0.00
Zero error of Power Sensor 0.00
Power Meter Linearity 0.04
Space Loss Measurement Error 0.01
Multipath Curve Fitting Random Error 0.04
Proximity Effect Correction Error 0.05
All expressed in dB and may be combined using the usual methods of
RMS, RSS, or worst case simple sum.

73's
Richard Clark, KB7QHC

Richard, I can agree with that
Wes obviously paid close attention to Reggies initial post
and replied in a way that was very informativeI and reflected
his knoweledge in that particular field
Nobody else came even close
to identifying Reggies needs and responded
in such a professional manner.

He should be congratulated
Regards
Art


"Richard Clark" wrote in message
...
On Tue, 26 Apr 2005 19:59:59 +0000 (UTC), "Reg Edwards"
wrote:

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.

Hi Reg,

I thought Wes' link was quite specific to the matter:
Measurement Mismatch Correction Error 0.04
Noise Power of Power Sensor 0.00
Zero error of Power Sensor 0.00
Power Meter Linearity 0.04
Space Loss Measurement Error 0.01
Multipath Curve Fitting Random Error 0.04
Proximity Effect Correction Error 0.05
All expressed in dB and may be combined using the usual methods of
RMS, RSS, or worst case simple sum.

73's
Richard Clark, KB7QHC

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.

On Wed, 27 Apr 2005 03:01:20 +0000 (UTC), "Reg Edwards"
wrote:

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.

Hi Reggie,

Measurement Mismatch Correction Error 0.04
Noise Power of Power Sensor 0.00
Zero error of Power Sensor 0.00
Power Meter Linearity 0.04
Space Loss Measurement Error 0.01
Multipath Curve Fitting Random Error 0.04
Proximity Effect Correction Error 0.05
The errors remain across all applications, only the assigned values
change. If I arbitrarily scaled all values by 25, few could challenge
the numbers.

At 7MHz we can all agree that the errors are going to be inversely
proportional to the astronomical cost to determine. No one is going
to perform it at HF when they can only afford 1/100th scale models
that offer the accuracies implied above. What would spending more
money buy them anyway?

73's
Richard Clark, KB7QHC

Well reasoned.

Think of a three-dimensional curve of cost, uncertainty, and frequency to
measure gain on a range. Think of a second 3D curve involving modeling. My
guess is that below something like 20 MHz (use your own number) modeling is
to be preferred.


On a related topic: I saw with my own eyes NBS in Boulder (c. 1978)
using a different technique to measure gain. It was a near field scheme
where a probe was moved in front of the antenna while its vector voltage and
position was measured. (As I recall, a pair of lasers was used in the
measurement of the probe's x and y position.) The (vast number of)
measurements were then imported into a computer that computed the gain. As
we say: "you could do that!" I never thought to ask what the expected
uncertainties were expected to be.
73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Richard Clark" wrote in message
...
On Wed, 27 Apr 2005 03:01:20 +0000 (UTC), "Reg Edwards"
wrote:

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.

Hi Reggie,

Measurement Mismatch Correction Error 0.04
Noise Power of Power Sensor 0.00
Zero error of Power Sensor 0.00
Power Meter Linearity 0.04
Space Loss Measurement Error 0.01
Multipath Curve Fitting Random Error 0.04
Proximity Effect Correction Error 0.05
The errors remain across all applications, only the assigned values
change. If I arbitrarily scaled all values by 25, few could challenge
the numbers.

At 7MHz we can all agree that the errors are going to be inversely
proportional to the astronomical cost to determine. No one is going
to perform it at HF when they can only afford 1/100th scale models
that offer the accuracies implied above. What would spending more
money buy them anyway?

73's
Richard Clark, KB7QHC

On Wed, 27 Apr 2005 09:26:48 -0400, "J. Mc Laughlin"
wrote:

Well reasoned.

Think of a three-dimensional curve of cost, uncertainty, and frequency to
measure gain on a range. Think of a second 3D curve involving modeling. My
guess is that below something like 20 MHz (use your own number) modeling is
to be preferred.


On a related topic: I saw with my own eyes NBS in Boulder (c. 1978)
using a different technique to measure gain. It was a near field scheme
where a probe was moved in front of the antenna while its vector voltage and
position was measured. (As I recall, a pair of lasers was used in the
measurement of the probe's x and y position.) The (vast number of)
measurements were then imported into a computer that computed the gain. As
we say: "you could do that!" I never thought to ask what the expected
uncertainties were expected to be.


http://www.nearfield.com/