Richard Clark wrote:

On Tue, 26 Apr 2005 20:28:01 -0500, Tom Ring
wrote:


Any references on microphone calibration? Maybe a short tutorial? That
is something I have a need to do.


Hi Tom,

As a second thought, you may not be in the market for the reciprocity
technique (it does require that you have a true reference microphone).

In that case, you would fall back to a Piston Phone and do a single
point calibration. The method is as old as the hills, the math is
extremely simple volumetrics, but the implementation (construction of
the calibration unit) is not something for the faint of heart. You
will need a precision lathe. Again, google using Brüel & Kjær as a
jump-off point.

Once you do the single point calibration, then you can proceed to a
swept frequency analysis. Unfortunately this returns us to the
necessity of a reference microphone. However, as relative frequency
response is more available (from expensive retail models), you might
have a chance.

73's
Richard Clark, KB7QHC

And thanks for this also.

I had a nicely useful, yellow, roughly 11x14, hardcover book that was a
handy audio manual that was lost during moving a couple decades ago. It
covered beginning through midrange complexity, and had a decent tutorial
on bi-amp. Also had a description of Indy Speedway Pit announcement
system, high sound pressure level, baseball stadium sound system, and
R&R, may have been The Grateful Dead. I think it may have been a
husband and wife team that wrote it. Ring any bells? I'd like to order
a copy of it.

tom
K0TAR

Roy Lewallen wrote:

Correction. Even identical array elements *don't* necessarily extract
the same amount of energy. The reason again is mutual coupling. In a
four-square receiving array with very low ground loss, one of the
elements will actually radiate power. This power comes from power
extracted from the wave by the other three. In a Yagi array, the
parasitic elements extract no power at all from an impinging wave; only
the driven element does.

Roy Lewallen, W7EL

Another example that can be divorced from ground effects and easily
modeled in free space is a 4 by 4 array of yagis - an EME array. The
corners are one set, the outside horizontal pairs are another, the
outside vertical pairs are another, and the inside 4 are another.

I have a simple 4 by 4 by 3 element AO array as an example if anyone
would like a copy.

tom
K0TAR

On Wed, 27 Apr 2005 20:26:10 -0500, Tom Ring
wrote:

Ring any bells? I'd like to order
a copy of it.

Hi Tom,

Sorry, no bells not even decibells.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Tue, 26 Apr 2005 21:09:07 -0700, Roy Lewallen
wrote:


I believe "takeoff angle" is in the same category as "capture area" and
"S-unit" -- terms which nobody except amateurs seem to need.


Hmmm,

Capture area of antennas, 899, 927 of Terman's "Electronic and Radio
Engineering. The 899 reference appeals to aperture. The 927
reference gives a value of 1.5 or 0.12 lambda² (also called intercept
area or antenna cross section) for a common dipole.
. . .

I stand corrected. Spurred by your response to do a more exhaustive
search, I found "capture area" in the indices of 3 out of the 12 antenna
texts and handbooks I have, plus in Terman's _Radio Engineering_. While
aperture is more commonly used (judging by this sample), "capture area"
is indeed in use outside the amateur community.

Think I'm likely to find "S-Unit" if I look hard enough?

Roy Lewallen, W7EL

J. Mc Laughlin wrote:
I too am reluctant to enter this as much resembles a freshman poli-sci
student debating a third year law student.

However .... please see indented comments below

. . .

Here I must inject my experience. As part of a topic sentence, "tends to be
the same" is OK. However, it is common on real HF paths of over 4 or 5 Mm
for the elevation angle at which the strongest signal arrives to be
significantly different at the two ends of the path. It is easy on longer
paths for the major mode at one end to be using a high virtual-height F2
mode and for the other end to be using a low virtual-height E mode.

Allow me to put to rest the notion that optimum elevation angles are
necessarily the same at both ends of a longer (multiple hop) HF path! [Reg
did not say that optimum elevation angle are necessarily the same.]

. . .

I'm glad you did get yourself to contribute to the discussion. I'm by no
means an expert when it comes to propagation (and quite apparently
several other participants aren't either), and I've fallen victim to
using oversimplified models where their use isn't appropriate. The
little reading I've done on the topic shows there are some really
interesting phenomena involved which don't at all fit with the notion of
simple reflection or refraction from a layer at a single height. Thanks
for reminding us about one of the more important ways in which the
simplified models are misleading.

As other have said, but not all have heard, the idea is to maximize gain
(at both ends of a path) at the elevation angle being used. Even in the
20s, antenna systems were in regular use that attempted to do just this.

. . .

Even if it were possible to do so, one would not use an antenna that had all
of its gain at the predicted optimum elevation angle. One would try to
design an antenna (money enters here) that has most of its gain in the
expected band of elevation angles expected to be best for a path.


Agreed.

Roy Lewallen, W7EL

Richard Harrison wrote:
My original comment was in support of Arnold B. Bailey who said
something about increasing antenna gain by 3 dB every time you double
its size. Precisely, that`s not true, but I gave an example from Kraus
where he did much the same thing.

+3dB is a valid generalization, based on sound physics - but it is only
a generalization.

At the time those Grand Old Men were writing their textbooks, such
generalizations were the best that anybody could manage. But they had no
way of checking their accuracy - or more important, why and when they
start to become INaccurate.

50 years on, we do have a way, and we now know much more than they did.
That makes it very dangerous to quote those Grand Old Generalizations as
accurate and universal truths. Richard was quite correct to describe the
"+3dB rule" as "naive" - because, at today's level of knowledge, it is.

But we still need to know that the +3dB generalization exists; and
understand the fundamental reasons for it. That fundamental
understanding is what protects us against stupid mistakes.


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

On Thu, 28 Apr 2005 00:11:44 -0700, Roy Lewallen
wrote:

Think I'm likely to find "S-Unit" if I look hard enough?

Hi Roy,

One could see stars in the middle of the day if they squint their eyes
hard enough. Seems to me Collins literature covered S Units
adequately and they were certainly the Cadillac of the pro's.
Hammerlund is another probable source. National another. RCA as
early as 1941.

On the other hand, I certainly wouldn't waste my eyes scanning the
shelves of the engineering library.

73's
Richard Clark, KB7QHC

"Ian White GM3SEK" wrote
Richard Harrison wrote:
My original comment was in support of Arnold B. Bailey who said something
about increasing antenna gain by 3 dB every time you double its size.
Precisely, that`s not true, but I gave an example from Kraus where he did
much the same thing.

+3dB is a valid generalization, based on sound physics - but it is only a
generalization. At the time those Grand Old Men were writing their
textbooks, such generalizations were the best that anybody could manage.
_______________

No doubt the 'GOM' knew the exact gain changes from successive doublings of
an antenna aperture, or could calculate them if they wished to. The
difference between the two isn't very important except when it is part of
the equation to arrive at some legally required ERP, such as in commercial
broadcasting.

Below are the gains of a series of commercial FM broadcast transmit arrays
to illustrate the point. The elements (bays) in these arrays all are one
wavelength apart, and driven with equal power and phase.

# Elements C-pol Gain (dBd)
1 -3.55
2 -0.21
4 3.09
8 6.34

Starting with the gain of the 1-bay and adding exactly 3 dB per doubled
aperture in this example would result in 5.45 dBd gain for the 8-bay,
meaning that FM ERP when using this approach would be more than 18% below
its licensed value (illegal).

RF

On Thu, 28 Apr 2005 00:40:11 -0700, Richard Clark
wrote:

On Thu, 28 Apr 2005 00:11:44 -0700, Roy Lewallen
wrote:

Think I'm likely to find "S-Unit" if I look hard enough?

Yep.



Hi Roy,

One could see stars in the middle of the day if they squint their eyes
hard enough. Seems to me Collins literature covered S Units
adequately and they were certainly the Cadillac of the pro's.
Hammerlund is another probable source. National another. RCA as
early as 1941.

On the other hand, I certainly wouldn't waste my eyes scanning the
shelves of the engineering library.

Scanning my library I spy:

"Fundamentals of Single Side Band", 2nd Edition, Sept 1959, Collins
Radio Company, Cedar Rapids, Iowa.

On page 13-7, in describing the circuitry of the 75S-1 it says in
part:

"The S-meter is calibrated in S-units and dB. The S-unit scale is
standard up to midscale (S-9). The db scale reads relative signal
strength above the avc threshold which is approximately 1 microvolt.
Thus 40 dB on the meter is 100 microvolts of signal (which also
corresponds to S-9 on the S-unit scale). To read dB over S-9 on the
S-unit scale, subtract 40 from the corresponding dB reading. For
instance, a 60-dB reading would be 20 dB over S-9 (100 uv) or 10,000
uv of signal at the antenna. This reading is then 60 dB over the dB
scale reference of one microvolt and 20 dB over the S-9 reference of
100 uv"

Whew.

Next to it I find:

"Amateur Single Sideband", 1st Edition, 1962, Collins Radio Company,
Cedar Rapids, Iowa.

Its only reference to S-meters is on page 111 where, in a section on
distortion tests with a receiver, it states in part:

"Variations and nonlinearities in S-meter calibration can introduce
considerable error in the measurement of signal levels by means of a
receiver. The commonly used figure of 6 dB per S-unit is appreciably
higher than the actual response of many amateur receivers. The meter
in the S-Line receivers, for instance, is calibrated to read
approximately S-9 with and input signal of 100 microvolts. The agc
threshold is set nominally to 1.5 microvolts, and varies slightly from
band to band. Therefore, the total range from S-zero to S-9 under
normal conditions can represent 30 to 40 dB or from approximately 3.3
to slightly over 4 dB per S-unit."

On Thu, 28 Apr 2005 00:40:11 -0700, Richard Clark
wrote:

On Thu, 28 Apr 2005 00:11:44 -0700, Roy Lewallen
wrote:

Think I'm likely to find "S-Unit" if I look hard enough?

Yep.



Hi Roy,

One could see stars in the middle of the day if they squint their eyes
hard enough. Seems to me Collins literature covered S Units
adequately and they were certainly the Cadillac of the pro's.
Hammerlund is another probable source. National another. RCA as
early as 1941.

On the other hand, I certainly wouldn't waste my eyes scanning the
shelves of the engineering library.

Scanning my library I spy:

"Fundamentals of Single Side Band", 2nd Edition, Sept 1959, Collins
Radio Company, Cedar Rapids, Iowa.

On page 13-7, in describing the circuitry of the 75S-1 it says in
part:

"The S-meter is calibrated in S-units and dB. The S-unit scale is
standard up to midscale (S-9). The db scale reads relative signal
strength above the avc threshold which is approximately 1 microvolt.
Thus 40 dB on the meter is 100 microvolts of signal (which also
corresponds to S-9 on the S-unit scale). To read dB over S-9 on the
S-unit scale, subtract 40 from the corresponding dB reading. For
instance, a 60-dB reading would be 20 dB over S-9 (100 uv) or 10,000
uv of signal at the antenna. This reading is then 60 dB over the dB
scale reference of one microvolt and 20 dB over the S-9 reference of
100 uv"

Whew.

Next to it I find:

"Amateur Single Sideband", 1st Edition, 1962, Collins Radio Company,
Cedar Rapids, Iowa.

Its only reference to S-meters is on page 111 where, in a section on
distortion tests with a receiver, it states in part:

"Variations and nonlinearities in S-meter calibration can introduce
considerable error in the measurement of signal levels by means of a
receiver. The commonly used figure of 6 dB per S-unit is appreciably
higher than the actual response of many amateur receivers. The meter
in the S-Line receivers, for instance, is calibrated to read
approximately S-9 with and input signal of 100 microvolts. The agc
threshold is set nominally to 1.5 microvolts, and varies slightly from
band to band. Therefore, the total range from S-zero to S-9 under
normal conditions can represent 30 to 40 dB or from approximately 3.3
to slightly over 4 dB per S-unit."