"Ian White GM3SEK" wrote in message
...
wrote:
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.

I don't think Richard is attempting to deny that.

The question is about lab techniques and error measurement and
Richards post was in answer to that.
Another person insinuated that a person who
tests against a dipole and measures after a skip has taken place is in Lu
Lu land because he assumed he was literally describing a normal
lab test of comparing to a dipole!

Remember, Richard was replying to the initial post which was
very specific in nature regarding lab testing and degree of error !
Assumption has no part in a real laboratory.

His tests were not intended to measure the gain of the antenna. They were
intended to answer a much more practical question: "How much stronger is
the signal from the curtain array, as delivered into the BC target area,
compared with using a dipole?" That's what the station owners wanted to
know, and they specifically wanted that answer to include all the
variables of antenna patterns and ionospheric propagation.

I could not agree more and stated so in my last post


As you have correctly pointed out, in any environment except free space,
that number is not the same as the antenna gain in dBd. Anybody who has
thought about it is aware of the problem, and that clearly includes
Richard.

Then why is he introducing dbi into the subject using Kraus as a backup?
Why does he state that TOA are "usually" the same when the opposite is true
especially when comparing a curtain to a dipole ? I don't believe that to be
correct
In the absence of denial by a guru must I assume he is correct or he meant
something else
and everybody knows what he said is true?

So you agree with the poster who stated that if a person thought that a
dipole comparison test consistes of comparing after skip took place,
is in Lu Lu land?

Everybody agrees with you, so you can stop banging on that open door.
They do ....????

And the question regarding propagation and antenna function can we assume
he is correct on that also ? I don't like to "assume" that he meant
something different
and let the newbies as well as I to be lead astray.
Must I assume he is correct in that last sentence he made
where I am asking for a corroborating technical written statement ?
Richards last statment was /is an echo of a similar posting made a few
months ago and the Gurus said nothing to confirm or deny it's voracity?.
What are we meant to assume , that if a guru doesn't question it
it must be correct? I personally would rather see corrobaration
in a accepted technical writing than set up the beginnings of an old wives
tale
The old saying is still true , don't rely on one gurus answer, ask another
and then another and ensure that context is correct.
I await Richards response with interest so that I may read an authoritive
statement for myself without the need for "assumption" as to what he
"really"
meant to say but didn't. If you know what he "meant" to say on that last
remaining subject why not supply a helping hand ?

Art

--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Art Unwin wrote:
"---may I go back to the "compared to a dipole" statement which Richard
keeps brushing off."

I accept a resonant dipole reference as a given.

It is true that the antenna under test and the reference dipole have
different radiation patterns. Our goal was to compare received signal
strengths at locations of interest.

The assumption was that on average, the propaqgation was nearly the same
for the signals received from both transmitting antennas. Good or bad
propagation, the difference between the signals depended on gain in the
direction of the receiver as the transmitted power was the same to both
antennas no matter where it landed.

Kraus says on page 535 of his 3rd edition of "antennas":
"Suppose that we express the gain with respect to a single lambda/2
element as the reference antenna. Let the same power P be supplied to
this antenna. Then assuming no heat losses, the current Io is the sq rt
of the power divided by the resistance of the reference antenna.

In general, the gain in field intensity of an array over a reference
antenna is given by the ratio of the field intensity from the array to
the field intensity from the reference antenna when both are supplied
with the same power P."

Kraus` example was our intended case.

Our expectations were met and our contractors were paid.

Best regards, Richard Harrison, KB5WZI

On Tue, 26 Apr 2005 00:04:02 -0700, Richard Clark
wrote:

On Mon, 25 Apr 2005 14:48:38 -0700, Wes Stewart
wrote:

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


Hi All,

The method described by the paper offered above is a commonplace of
Metrology called "Reciprocity." I have calibrated precision
microphones against this method, and the error math offered is
consistent with my experience (much less the actual values offered as
examples).

It is also a method used for determining the phase noise of low noise
oscillators.


As an aside, this method is also as old as the pyramids - literally.
The Egyptians planned their blocks of granite to have nearly flat
faces to within 10s of microinches using three blocks, by abrading one
against the other and then rotating their positions.

Accuracy is far more a matter of protocol or technique than it is
about a ruler (or other scale).

73's
Richard Clark, KB7QHC

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.

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.

"Richard Harrison" wrote
The assumption was that on average, the propaqgation was nearly the same
for the signals received from both transmitting antennas. Good or bad
propagation, the difference between the signals depended on gain in the
direction of the receiver as the transmitted power was the same to both
antennas no matter where it landed.

"Propagation" has to include ALL means by which EM energy radiated from a
wire antenna finally arrives at a receiving location. That necessarily
includes the radiation effects of reflecting/obstructing objects and
surfaces, each of which may be illuminated by varying ERP from the wire
antenna -- depending on the radiation envelope of the wire antenna itself,
its installation detail, and site topology.

The ERP directed toward a particular receiving site depends on more than the
free space gain of the tx antenna along a single launch angle (which I
believe is Art's point).

RF

Art Unwin wrote:
"Remember, Richard was replying to the initial post which was very
specific in nature regarding lab testing and degree of error."

Antenna test facilities involve far fields. Kraus says on page 831 of
his 3rd edition of "Antennas":
"---it is obvious that measurement usually takes place in the far
field."

This can be far indeed with highly directive antennas.

My initial response included:
"A lab may put its stamp of approval on your instrument, but your best
assurance may be measurement of known values. The termperature of
ice-water or the voltage of new dry cells, for example. You usually can
try several dry cells for confirmation or averaging.

In antennas, one strategy for successful gain determination is
comparison with an antenna of known gain."

My posting was imperfect. There`s nothing that can`t be improved, but
were I re-writing my posting, I can`t think how I might improve it.

I don`t think my example of checking gain of an array using skywaves was
amiss. We build shortwave antennas to use skywaves. We give antenna
gains in free-space because it makes sense.

I said we built a small-scale model first because we can measure the
model`s characteristics without a helicopter. The full-scale antenna
performed exactly like the model. Computer modeling has eliminated the
small-scale model step in new designs.

We checked only the first off of the new design, with the full
confidence that subsequent antennas of the same design would perform the
same.

Of the first antenna, we measured everything including the currents
along each element. We used an R-F ammeter in a loop suspended from the
element and towed along with a string. We read it using a telescope. The
antenna was a scientific success as well as a practical success. This
differs from some of the oil wells I was to drill later, though some of
those succeeded too.

I can only post what I know and it will never satisfy what everybody
wants to read. Sometimes my postings are more responsive than others.
That`s part of the fun.

Best regards, Richard Harrison, KB5WZI

Richard,
You are at it again, avoiding the supply of corroberation to what you say
is true.
Stick to the basic statement that you made, which from their silence, the
gurus concur
with.
Your statement was that:
propagation is what determines TOA
and I ask for confirmation of the correctness of that
statement from you in the nature of some written text.
The gurus obviously accept your statement as fact, but I do not.
Usually you refer to a text to back up your statement ,but this time you
haven't, winging it
and relying solely on the fact that the gurus agree with you.
Surely you or some guru can come up
with a written text that states that propagation is what determine TOA.!
That is what this group is all about where gurus debunk the untruths
and supply the real truths and not to let old wives tale dominate.
You also stated that you made the ":assumption" presumably
based on the "facts" stated above that the Curtain could be considered as
similar to the dipole
since propagation determines that they are the same. This is total junk ,in
its entirety,
unless you or the gurus can come up with a written text that confirmes their
positions.
Art


"Richard Harrison" wrote in message
...
Art Unwin wrote:
"---may I go back to the "compared to a dipole" statement which Richard
keeps brushing off."

I accept a resonant dipole reference as a given.

It is true that the antenna under test and the reference dipole have
different radiation patterns. Our goal was to compare received signal
strengths at locations of interest.

The assumption was that on average, the propaqgation was nearly the same
for the signals received from both transmitting antennas. Good or bad
propagation, the difference between the signals depended on gain in the
direction of the receiver as the transmitted power was the same to both
antennas no matter where it landed.

Kraus says on page 535 of his 3rd edition of "antennas":
"Suppose that we express the gain with respect to a single lambda/2
element as the reference antenna. Let the same power P be supplied to
this antenna. Then assuming no heat losses, the current Io is the sq rt
of the power divided by the resistance of the reference antenna.

In general, the gain in field intensity of an array over a reference
antenna is given by the ratio of the field intensity from the array to
the field intensity from the reference antenna when both are supplied
with the same power P."

Kraus` example was our intended case.

Our expectations were met and our contractors were paid.

Best regards, Richard Harrison, KB5WZI

"Takeoff angle" can have two meanings. The first, and really a misuse of
the term, is the one used by antenna modeling programs such as EZNEC. It
means the elevation angle at which an antenna's radiation is maximum.
This is a property of the antenna and its local environment
(particularly the height above ground for horizontal antennas, and local
ground quality for vertical antennas).

The second meaning is the elevation angle at which propagation occurs.
This is dictated mainly by the propagation path -- the distance and the
effective height of the ionosphere. The antenna pattern can play a role
only when more than one path is possible, for example single and double
hop, by modifying the amount which propagates by each path. The "takeoff
angle" of the first meaning (angle at which the radiaion is maximum)
isn't a particularly useful measure of and antenna's performance, and it
certainly doesn't determine the real "takeoff angle" of the second
meaning (angle at which propagation occurs).

Art has used "takeoff angle" of the first meaning liberally in his
writings, often with the added and incorrect implication that all the
radiation from an antenna occurs at its "takeoff angle", with none at
other elevation angles. So his confusion about Richard's statement
(which correctly used "takeoff angle" in the second sense) is
understandable.

Roy Lewallen, W7EL

wrote:
Richard,
You are at it again, avoiding the supply of corroberation to what you say
is true.
Stick to the basic statement that you made, which from their silence, the
gurus concur
with.
Your statement was that:
propagation is what determines TOA
and I ask for confirmation of the correctness of that
statement from you in the nature of some written text.
The gurus obviously accept your statement as fact, but I do not.
Usually you refer to a text to back up your statement ,but this time you
haven't, winging it
and relying solely on the fact that the gurus agree with you.
Surely you or some guru can come up
with a written text that states that propagation is what determine TOA.!
That is what this group is all about where gurus debunk the untruths
and supply the real truths and not to let old wives tale dominate.
You also stated that you made the ":assumption" presumably
based on the "facts" stated above that the Curtain could be considered as
similar to the dipole
since propagation determines that they are the same. This is total junk ,in
its entirety,
unless you or the gurus can come up with a written text that confirmes their
positions.
Art

Art Unwin wrote:
"Surely you or some guru can come up with written text that states that
propagation is what determines TOA."

I don`t find TOA in any index. I find "elevation angle", which I suppose
is a synonym, in my 19th edition of The ARRL Antenna Book. On page 2-9
it says:
"The elevation angle is referenced to the horizon at the earth`s surface
, where the elevation angle is 0-degrees."

On page 3-5, the same book says:
"Now look at Fig. 4A, which compares the computed vertical-angle
response for two half-wave dipoles at 14 MHz."

The Antenna Book is not very definitive.

"Transmission Lines, Antennas, and Wave Guides" on page 314 says:
In order to escape from the earth without excessive ground attenuation,
a sky wave must leave the earth at an angle of at least 3-degrees above
the horizon.---At 3-degrees elevation, the distance per hop is about
3,500 km (2,100 miles). Longer distances are automatically broken up
into units not exceeding 3.500 knm."

It`s the medium breaking up the hops, not the antenna.

Best regards, Richard Harrison, KB5WZI

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.