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OT+DC was Re: [TekScopes] 2465 Calibration

 

On 2022-04-30 2:25 p.m., Jeff Dutky wrote:
On Sat, Apr 30, 2022 at 09:27 AM, <toby@...> wrote:

On 2022-04-30 9:18 a.m., Raymond Domp Frank wrote:
On Sat, Apr 30, 2022 at 12:49 AM, si_emi_01 wrote:


No one tells you that when they say "signal" they mean the Square Wave not the DC Level Output.
In a cocky mood I'd say a DC level is not a signal; it contains no information. Switching a DC level on or off however is.
In a quibbling mood I might point out that DC is frequently defined as "current flowing in one direction" without implying a fixed potential :)
but if there is any variation in potential then you can select an arbitrary ground potential that will result in some portion of the signal have a reversed flow of current, so the only unquestionably direct current signal is also a signal with unvarying potential. (I can quibble with the best of them!)
I didn't make it up. Take it up with the textbooks, or, indeed, wikipedia :)

(Quibble^2: There is no such thing as an unvarying potential in the real world.)

(I admit for many years I too assumed a more or less fixed potential, probably because that's the most common subset of DC that we encounter. It was only more recently that I learned the more general definition.)

--T



-- Jeff Dutky
 

It all comes down to resolution of time and level.

I have never seen a DC Source (even a battery can be exposed to an Electromagnetic field and vary its amplitude), nor anything to measure it with total uncertainty.

Everything is exposed to Electromagnetic fields whether in a 100dB double Faraday shielded chamber, out in the desert, deep ocean, space. There are always Electromagnetic fields - even gravity.

Ross

-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of toby@...
Sent: Saturday, April 30, 2022 12:57 PM
To: [email protected]
Subject: OT+DC was Re: [TekScopes] 2465 Calibration

On 2022-04-30 2:25 p.m., Jeff Dutky wrote:
On Sat, Apr 30, 2022 at 09:27 AM, <toby@...> wrote:

On 2022-04-30 9:18 a.m., Raymond Domp Frank wrote:
On Sat, Apr 30, 2022 at 12:49 AM, si_emi_01 wrote:


No one tells you that when they say "signal" they mean the Square Wave not the DC Level Output.
In a cocky mood I'd say a DC level is not a signal; it contains no information. Switching a DC level on or off however is.
In a quibbling mood I might point out that DC is frequently defined
as "current flowing in one direction" without implying a fixed
potential :)
but if there is any variation in potential then you can select an
arbitrary ground potential that will result in some portion of the
signal have a reversed flow of current, so the only unquestionably
direct current signal is also a signal with unvarying potential. (I
can quibble with the best of them!)
I didn't make it up. Take it up with the textbooks, or, indeed, wikipedia :)

(Quibble^2: There is no such thing as an unvarying potential in the real
world.)

(I admit for many years I too assumed a more or less fixed potential, probably because that's the most common subset of DC that we encounter.
It was only more recently that I learned the more general definition.)

--T



-- Jeff Dutky
 

On Sat, Apr 30, 2022 at 09:33 PM, si_emi_01 wrote:

Since this seems very important to you, I'll respond, embedded, after your text


It all comes down to resolution of time and level.

I have never seen a DC Source (even a battery can be exposed to an
Electromagnetic field and vary its amplitude)
I tend to "agree", since everything is (almost) always exposed to some electromagnetic field, however weak and a theoretical DC Source has no amplitude, by the definition of amplitude.

nor anything to measure it with
total uncertainty.
An egg alarm as an example would come close


Everything is exposed to Electromagnetic fields whether in a 100dB double
Faraday shielded chamber, out in the desert, deep ocean, space. There are
always Electromagnetic fields - even gravity.
What were the guys at Tek thinking, trying to produce and sell a device with a "DC Level Output"? How silly!
We're getting into "everything is uncertain and even that is uncertain" territory.
I'm done with this.

Raymond
 

On Sat, Apr 30, 2022 at 12:33 PM, si_emi_01 wrote:


There are always Electromagnetic fields - even gravity
To be clearer, if not somewhat pedantic, there are fields everywhere: electromagnetic, gravitational, strong weak.
Although general relativity shows light conforms to the curvature of space-time, gravity is usually only relevant to Tek when it comes to Series 500 scopes.
This is a theory of gravity your back with appreciate, if you don't verify it.

--
Roy Thistle
 

On Sat, Apr 30, 2022 at 01:11 PM, Raymond Domp Frank wrote:


and a theoretical DC Source has no amplitude, by the definition of amplitude
0 VDC = A Sin(wt) VAC, where w = 2 x pi x f, for all t, and only when f = 0
which is the type of stuff we often argue about.
--
Roy Thistle
 

I don't see what all the fuss is about in this offshoot of the original thread (2465 calibration). Disregarding the semantics, and "exact" definitions of things, I view DC just as valid as a "probe adjust" "signal." In a communications sense, neither carries any information, but in a utility sense, DC provides an amplitude, while the square wave provides an amplitude and some constant timing, but that's all.

Power signals have discrete spectra (steady-state), so just like a pure sinewave at some frequency f, where all the power is concentrated, a DC signal has all its power at zero frequency. 1 Vrms of 1 kHz or 1 VDC on 50 ohms is still +13 dBm. Neither carries any information as-are, but when some form of modulation is applied, the spectral content changes, and you can convey information.

So anyway, the DC and the probe adjust signals have utility for adjusting things, because they are well defined things that we can compare to, but don't carry any information. I remember many decades ago, a prof in one of my communications classes put it succinctly. We were having a class discussion on noise, interference, and error correction etc, and practical trade-offs involved. He said something like "if you already know everything about the signal information to be transmitted, you can have perfect communications, but then there's no need to send it - the information capacity is zero."

Ed
 

Or, to paraphrase Shannon, "information is surprise."

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

On 5/1/2022 12:51, Ed Breya via groups.io wrote:
I don't see what all the fuss is about in this offshoot of the original thread (2465 calibration). Disregarding the semantics, and "exact" definitions of things, I view DC just as valid as a "probe adjust" "signal." In a communications sense, neither carries any information, but in a utility sense, DC provides an amplitude, while the square wave provides an amplitude and some constant timing, but that's all.

Power signals have discrete spectra (steady-state), so just like a pure sinewave at some frequency f, where all the power is concentrated, a DC signal has all its power at zero frequency. 1 Vrms of 1 kHz or 1 VDC on 50 ohms is still +13 dBm. Neither carries any information as-are, but when some form of modulation is applied, the spectral content changes, and you can convey information.

So anyway, the DC and the probe adjust signals have utility for adjusting things, because they are well defined things that we can compare to, but don't carry any information. I remember many decades ago, a prof in one of my communications classes put it succinctly. We were having a class discussion on noise, interference, and error correction etc, and practical trade-offs involved. He said something like "if you already know everything about the signal information to be transmitted, you can have perfect communications, but then there's no need to send it - the information capacity is zero."

Ed
 

That's really good, Tom! I'm going to have to remember that one.

Nice explanation as well, Ed.

Thanks.

Jim Ford

------ Original Message ------
From: "Tom Lee" <tomlee@...>
To: [email protected]
Sent: 5/1/2022 2:58:06 PM
Subject: Re: OT+DC was Re: [TekScopes] 2465 Calibration

Or, to paraphrase Shannon, "information is surprise."

--Tom

-- Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070


On 5/1/2022 12:51, Ed Breya via groups.io wrote:
I don't see what all the fuss is about in this offshoot of the original thread (2465 calibration). Disregarding the semantics, and "exact" definitions of things, I view DC just as valid as a "probe adjust" "signal." In a communications sense, neither carries any information, but in a utility sense, DC provides an amplitude, while the square wave provides an amplitude and some constant timing, but that's all.

Power signals have discrete spectra (steady-state), so just like a pure sinewave at some frequency f, where all the power is concentrated, a DC signal has all its power at zero frequency. 1 Vrms of 1 kHz or 1 VDC on 50 ohms is still +13 dBm. Neither carries any information as-are, but when some form of modulation is applied, the spectral content changes, and you can convey information.

So anyway, the DC and the probe adjust signals have utility for adjusting things, because they are well defined things that we can compare to, but don't carry any information. I remember many decades ago, a prof in one of my communications classes put it succinctly. We were having a class discussion on noise, interference, and error correction etc, and practical trade-offs involved. He said something like "if you already know everything about the signal information to be transmitted, you can have perfect communications, but then there's no need to send it - the information capacity is zero."

Ed
 

On 5/1/2022 1:13 PM, Roy Thistle wrote:
On Sat, Apr 30, 2022 at 12:33 PM, si_emi_01 wrote:

There are always Electromagnetic fields - even gravity
To be clearer, if not somewhat pedantic, there are fields everywhere: electromagnetic, gravitational, strong weak.
Although general relativity shows light conforms to the curvature of space-time, gravity is usually only relevant to Tek when it comes to Series 500 scopes.
This is a theory of gravity your back with appreciate, if you don't verify it.
As I approach 90 ( I'm 88 ) 7K scopes are a lot heavier that they used to be also.
 

On Sun, May 1, 2022 at 02:02 PM, Jim Ford wrote:


I'm going to have to remember that one.
It doesn't surprise me.
Just remember that information is sometimes defined as the logarithm of the probability: or, In = log (prob(x) ), where In is the numerical value of the information.
The devil is in the details of the probability distribution.
An information in this way isn't usually what we are thinking about when we think of "information."
But, if you have certainty, you have a probability of 1: hence, an In = 0.
An apparently, there is always, however small, a chance that a particular event will occur.

--
Roy Thistle
 

Yup.

My first Oscilloscope was a Tektronix 551 back in 1979. It had 98 Tubes.

It had 2 parts. The Oscilloscope and a separate Power Supply. I located the Power Supply under my bench on a step stool.

They didn't put two handles on the Oscilloscope for no reason...


Ross

-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of Roy Thistle
Sent: Sunday, May 01, 2022 11:13 AM
To: [email protected]
Subject: Re: OT+DC was Re: [TekScopes] 2465 Calibration

On Sat, Apr 30, 2022 at 12:33 PM, si_emi_01 wrote:


There are always Electromagnetic fields - even gravity
To be clearer, if not somewhat pedantic, there are fields everywhere: electromagnetic, gravitational, strong weak.
Although general relativity shows light conforms to the curvature of space-time, gravity is usually only relevant to Tek when it comes to Series 500 scopes.
This is a theory of gravity your back with appreciate, if you don't verify it.

--
Roy Thistle

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