signal generator output

[John Larkin]

On 13 Dec 2010 08:58:02 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

On 2010-12-11, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

No. Given a 50 ohm generator driving a 50 ohm cable, open on the far
end, the end of the coax looks like a 50 ohm source. The transmission
line doesn't look like an attenuator unless it's lossy, which effect
will be negligable for a few feet of RG58 at reasonable frequencies.

not really. the unterminated end of the coax looks like a mirror,
asif the coax continued for the same length to an identical source
producing an identical signal.

Really. Assume a shielded black box with a coax connector coming out
one face. We know that there is an ideal 50 ohm signal generator
inside, with an ideal 50 ohm coax of unknown length inside, between
the generator and the connector to the outside. The generator
conveniently makes flat frequency sweeps, square wave sweeps, DC
levels, and unit impulses from time to time. We know everything about
the levels and waveforms except exactly when each is begun.

There no way to make measurements on that signal from outside the box
that tells you whether there is a piece of coax inside the box, or how
long it might be. The connector just looks like a 50 ohm source.

John

 

[John Fields]

On Mon, 13 Dec 2010 08:03:58 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 13 Dec 2010 08:02:50 -0600, John Fields
jfields@austininstruments.com> wrote:

On Sun, 12 Dec 2010 18:27:50 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 12 Dec 2010 19:23:27 -0600, John Fields
jfields@austininstruments.com> wrote:

On Sun, 12 Dec 2010 10:16:50 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 12 Dec 2010 05:05:05 -0600, John Fields
jfields@austininstruments.com> wrote:

On Sun, 12 Dec 2010 12:04:34 +1100, "Phil Allison" <phil_a@tpg.com.au
wrote:


"John Fields"


** I set up the same conditions as the OP described - ie an RF generator,
1.5 meters of RG58 co-ax and a 60MHz scope with 1 Mohm //20pF input.

AS EXPECTED the input impedance of the cable dips sharply at the quarter
wave frequency, 22MHz for my set up - or 28 MHz if the cable is left
completely unterminated. This was determined by monitoring the signal at the
output connector of the RF gen with a 10:1 probe.

However, at the scope end of the cable there is little sign of any dipping
or peaking.

So, the cable acts like a quarter wave stub all right, but the unterminated
end has a fairly consistent signal level since peaking and dipping occur
simultaneously at opposite ends.

Sue as hell looks like standing waves at play to me.



.... Phil

---
I agree.

Run an AC analysis of:

news:5k49g6dkto6kak9k86v8fp5135kvqpi25q@4ax.com

and take a look at the inputs of the transmission lines for your
Himalayas!


But not at the scope. One normally doesn't open up a coax and probe
points internally.

---
Depends.

Ever heard of a slotted line?
---

"Standing waves" do not explain the OP's issue. A 50 ohm generator,
driving a 50 ohm coax, into a capacitive load, is flat at the load, up
to the -3 dB corner, roughly 200 MHz for a typical scope Cin. Then it
rolls off nicely at 6 dB/octave. There are no frequency peaks or dips
at the load.

---

From the 200MHz corner it rolls off at 3db per octave until it gets to
400MHz, and _then_ it rolls off at 6dB per octave after that.

It rolls off at all possible slopes from udB/octave far below the
corner to almost 6 dB/octave far above. I was describing the
asymptotic bahavior, which is the way people talk in this business.


---

Below the corner frequency, the scope sees the same voltage as the
unloaded generator would put out at its connector, at all frequencies,
no matter how long the cable is.

---
Well, being picky, and since the lowpass isn't a brickwall filter, not
really.

The RC forms a voltage divider, so as the reactance of the cap changes
with frequency, so also does the voltage into the scope even if the
output amplitude from the generator remains constant.

of course the change would be very small, far from the corner
frequency, but the output voltage from the generator and the output
from the divider still wouldn't be the same.
---

If you add a 50 ohm feedthru terminator at the scope, the amplitude
drops in half and the corner frequency doubles, independent of cable
length. Still no whoopy-doos.

---
Driving the line through, and terminating it with its characteristic
impedance makes it transparent, except for delay and attenuation
losses with regard to its length, so there's no surprise there.

I was somewhat taken aback by the change in the terminated VS
unterminated corner frequency until I realized that the current
divided between the cap and the load resistor.

Thanks for that.
---


(I have described the asymptotic behavior, which is usual in this
business. Don't get preachy about a dB or so near the corner
frequency.)

John

---
Your admonition falls on deaf ears and since, if it pleases me to do
so, why shouldn't I?

Because it makes you look ignorant.

---
You take almost every opportunity you can, including lying and
cheating, to try to make me look ignorant and now you're seemingly
concerned about it?

You do it to yourself.

---
I don't think so, and your snippage is telling...

I'm usually careful about what I post, and I count my P's and Q's, and
I mostly show my work so my thinking can be followed and any errors I
may make can be critiqued on that basis.

Kinda like peer review.

You, on the other hand, are dishonest in that you use subterfuge to
downplay your errors and you like to play fast and loose, so that when
anyone catches you in a technical error you use that looseness to
evade owning up to your errors and, instead, try to make it seem like
something was wrong with whoever caught your error.

---
JF

 

[John Larkin]

On Mon, 13 Dec 2010 19:46:03 -0600, John Fields
<jfields@austininstruments.com> wrote:

On Mon, 13 Dec 2010 08:03:58 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 13 Dec 2010 08:02:50 -0600, John Fields
jfields@austininstruments.com> wrote:

On Sun, 12 Dec 2010 18:27:50 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 12 Dec 2010 19:23:27 -0600, John Fields
jfields@austininstruments.com> wrote:

On Sun, 12 Dec 2010 10:16:50 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Sun, 12 Dec 2010 05:05:05 -0600, John Fields
jfields@austininstruments.com> wrote:

On Sun, 12 Dec 2010 12:04:34 +1100, "Phil Allison" <phil_a@tpg.com.au
wrote:


"John Fields"


** I set up the same conditions as the OP described - ie an RF generator,
1.5 meters of RG58 co-ax and a 60MHz scope with 1 Mohm //20pF input.

AS EXPECTED the input impedance of the cable dips sharply at the quarter
wave frequency, 22MHz for my set up - or 28 MHz if the cable is left
completely unterminated. This was determined by monitoring the signal at the
output connector of the RF gen with a 10:1 probe.

However, at the scope end of the cable there is little sign of any dipping
or peaking.

So, the cable acts like a quarter wave stub all right, but the unterminated
end has a fairly consistent signal level since peaking and dipping occur
simultaneously at opposite ends.

Sue as hell looks like standing waves at play to me.



.... Phil

---
I agree.

Run an AC analysis of:

news:5k49g6dkto6kak9k86v8fp5135kvqpi25q@4ax.com

and take a look at the inputs of the transmission lines for your
Himalayas!


But not at the scope. One normally doesn't open up a coax and probe
points internally.

---
Depends.

Ever heard of a slotted line?
---

"Standing waves" do not explain the OP's issue. A 50 ohm generator,
driving a 50 ohm coax, into a capacitive load, is flat at the load, up
to the -3 dB corner, roughly 200 MHz for a typical scope Cin. Then it
rolls off nicely at 6 dB/octave. There are no frequency peaks or dips
at the load.

---

From the 200MHz corner it rolls off at 3db per octave until it gets to
400MHz, and _then_ it rolls off at 6dB per octave after that.

It rolls off at all possible slopes from udB/octave far below the
corner to almost 6 dB/octave far above. I was describing the
asymptotic bahavior, which is the way people talk in this business.


---

Below the corner frequency, the scope sees the same voltage as the
unloaded generator would put out at its connector, at all frequencies,
no matter how long the cable is.

---
Well, being picky, and since the lowpass isn't a brickwall filter, not
really.

The RC forms a voltage divider, so as the reactance of the cap changes
with frequency, so also does the voltage into the scope even if the
output amplitude from the generator remains constant.

of course the change would be very small, far from the corner
frequency, but the output voltage from the generator and the output
from the divider still wouldn't be the same.
---

If you add a 50 ohm feedthru terminator at the scope, the amplitude
drops in half and the corner frequency doubles, independent of cable
length. Still no whoopy-doos.

---
Driving the line through, and terminating it with its characteristic
impedance makes it transparent, except for delay and attenuation
losses with regard to its length, so there's no surprise there.

I was somewhat taken aback by the change in the terminated VS
unterminated corner frequency until I realized that the current
divided between the cap and the load resistor.

Thanks for that.
---


(I have described the asymptotic behavior, which is usual in this
business. Don't get preachy about a dB or so near the corner
frequency.)

John

---
Your admonition falls on deaf ears and since, if it pleases me to do
so, why shouldn't I?

Because it makes you look ignorant.

---
You take almost every opportunity you can, including lying and
cheating, to try to make me look ignorant and now you're seemingly
concerned about it?

You do it to yourself.

---
I don't think so, and your snippage is telling...

I'm usually careful about what I post, and I count my P's and Q's, and
I mostly show my work so my thinking can be followed and any errors I
may make can be critiqued on that basis.

Kinda like peer review.

You, on the other hand, are dishonest in that you use subterfuge to
downplay your errors and you like to play fast and loose, so that when
anyone catches you in a technical error you use that looseness to
evade owning up to your errors and, instead, try to make it seem like
something was wrong with whoever caught your error.

What error did I make here? I predicted the frequency response the OP
would see, with the coax driving a hi-z scope input. I predicted he'd
see no frequency peaks or dips at the scope, just flat with a corner
around 200 MHz, and a 6 db/octave rolloff after that. Basic stuff,
actually.

You and Mr Personality predicted mountain ranges of peaks and dips
caused by standing waves.

You sim'd it and I was right. So why are you mad at me?

John

 

[Jasen Betts]

On 2010-12-13, John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On 13 Dec 2010 08:58:02 GMT, Jasen Betts <jasen@xnet.co.nz> wrote:

Really. Assume a shielded black box with a coax connector coming out
one face. We know that there is an ideal 50 ohm signal generator
inside, with an ideal 50 ohm coax of unknown length inside, between
the generator and the connector to the outside. The generator
conveniently makes flat frequency sweeps, square wave sweeps, DC
levels, and unit impulses from time to time. We know everything about
the levels and waveforms except exactly when each is begun.

There no way to make measurements on that signal from outside the box
that tells you whether there is a piece of coax inside the box, or how
long it might be. The connector just looks like a 50 ohm source.

Good explanation.
with a matched source the coax is immaterial, it's asif it wasn't there.


thanks.
--
⚂⚃ 100% natural

 

[John Fields]

On Mon, 13 Dec 2010 19:57:43 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 13 Dec 2010 19:46:03 -0600, John Fields
jfields@austininstruments.com> wrote:

I'm usually careful about what I post, and I count my P's and Q's, and
I mostly show my work so my thinking can be followed and any errors I
may make can be critiqued on that basis.

Kinda like peer review.

You, on the other hand, are dishonest in that you use subterfuge to
downplay your errors and you like to play fast and loose, so that when
anyone catches you in a technical error you use that looseness to
evade owning up to your errors and, instead, try to make it seem like
something was wrong with whoever caught your error.

What error did I make here? I predicted the frequency response the OP
would see, with the coax driving a hi-z scope input. I predicted he'd
see no frequency peaks or dips at the scope, just flat with a corner
around 200 MHz, and a 6 db/octave rolloff after that. Basic stuff,
actually.

You and Mr Personality predicted mountain ranges of peaks and dips
caused by standing waves.

You sim'd it and I was right. So why are you mad at me?

---
I'm not mad at you, I just don't like you.

Why? Basically, because you're nasty and sneaky when you don't get
your way or are found to be in error, and generally just
mean-spirited.

For instance, was that crack about Phil necessary? Of course not, and
all it can do is increase the enmity around here, which you seem wont
to do in an effort to belittle everyone else and exalt yourself, just
like Sloman does.

As far as the SWR thing goes, I went to the trouble of simulating it
to determine what the truth of the matter was, and accepted the result
which proved you were right.

Had you been wrong though, you'd still be dancing around looking for a
"What I meant was..." loophole to crawl through and generally blowing
a lot of smoke around in order to try to create confusion.

We all make mistakes, but you seem to be on a crusade bent on having
yours be seen as trivial, no matter how serious, and ours serious, no
matter how trivial.

---
JF

 

[John Larkin]

On Tue, 14 Dec 2010 07:03:37 -0600, John Fields
<jfields@austininstruments.com> wrote:

On Mon, 13 Dec 2010 19:57:43 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 13 Dec 2010 19:46:03 -0600, John Fields
jfields@austininstruments.com> wrote:

I'm usually careful about what I post, and I count my P's and Q's, and
I mostly show my work so my thinking can be followed and any errors I
may make can be critiqued on that basis.

Kinda like peer review.

You, on the other hand, are dishonest in that you use subterfuge to
downplay your errors and you like to play fast and loose, so that when
anyone catches you in a technical error you use that looseness to
evade owning up to your errors and, instead, try to make it seem like
something was wrong with whoever caught your error.

What error did I make here? I predicted the frequency response the OP
would see, with the coax driving a hi-z scope input. I predicted he'd
see no frequency peaks or dips at the scope, just flat with a corner
around 200 MHz, and a 6 db/octave rolloff after that. Basic stuff,
actually.

You and Mr Personality predicted mountain ranges of peaks and dips
caused by standing waves.

You sim'd it and I was right. So why are you mad at me?

---
I'm not mad at you, I just don't like you.

Why? Basically, because you're nasty and sneaky when you don't get
your way or are found to be in error, and generally just
mean-spirited.

This is a public forum. Play the game or whine.

For instance, was that crack about Phil necessary?

He shrieks and curses at everybody. Everybody. He deserves no respect,
and has demonstrated that it doesn't help. And his expertise stops at
20 KHz. Best thing to do is laugh at him, which at least makes him
useful.

Of course not, and

all it can do is increase the enmity around here, which you seem wont
to do in an effort to belittle everyone else and exalt yourself, just
like Sloman does.

Don't be silly. I'm friendly and helpful to anybody who is reasonably
sincere, and have made several personal in-the-flesh friends from
s.e.d. I post schematics. I send people parts. I'm polite to anyone
who is polite. Usenet does have an infinite supply of anonymous jerks,
and there's no reason to be polite to them.

YOU escalate after you post stuff that's wrong, which you do fairly
often. My earlier posts about the "standing wave" thing were factual.
If, at that point, you had checked your claims, you might have avoided
a dispute, and maybe learned something to boot. You and Phil jumped on
me when you should have been thinking.

As far as the SWR thing goes, I went to the trouble of simulating it
to determine what the truth of the matter was, and accepted the result
which proved you were right.

*AFTER* making silly and insulting statements.

I'm usually right because I post about stuff I know (I live
transmission lines) and because I'm (usually) careful.

Had you been wrong though, you'd still be dancing around looking for a
"What I meant was..." loophole to crawl through and generally blowing
a lot of smoke around in order to try to create confusion.

No. When I'm wrong I correct myself. It's no big deal top make a
mistake occasionally. When we actually lay out boards in my shop, we
design review and crosscheck exhaustively; I don't do that in
newsgroups, so of course I make the occasional mistake. Electronics is
complex, and newsgroups don't matter.

We all make mistakes, but you seem to be on a crusade bent on having
yours be seen as trivial, no matter how serious, and ours serious, no
matter how trivial.

I pointed out, in this case, that the OP would not see the effects of
standing waves at his scope input. No peaks, dips, mountain ranges.
The OP was being misled, lied to almost, and that was not trivial.

And I thought you plonked me.

John

 

[John Fields]

On Tue, 14 Dec 2010 08:36:05 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 14 Dec 2010 07:03:37 -0600, John Fields
jfields@austininstruments.com> wrote:

On Mon, 13 Dec 2010 19:57:43 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 13 Dec 2010 19:46:03 -0600, John Fields
jfields@austininstruments.com> wrote:

I'm usually careful about what I post, and I count my P's and Q's, and
I mostly show my work so my thinking can be followed and any errors I
may make can be critiqued on that basis.

Kinda like peer review.

You, on the other hand, are dishonest in that you use subterfuge to
downplay your errors and you like to play fast and loose, so that when
anyone catches you in a technical error you use that looseness to
evade owning up to your errors and, instead, try to make it seem like
something was wrong with whoever caught your error.

What error did I make here? I predicted the frequency response the OP
would see, with the coax driving a hi-z scope input. I predicted he'd
see no frequency peaks or dips at the scope, just flat with a corner
around 200 MHz, and a 6 db/octave rolloff after that. Basic stuff,
actually.

You and Mr Personality predicted mountain ranges of peaks and dips
caused by standing waves.

You sim'd it and I was right. So why are you mad at me?

---
I'm not mad at you, I just don't like you.

Why? Basically, because you're nasty and sneaky when you don't get
your way or are found to be in error, and generally just
mean-spirited.

This is a public forum. Play the game or whine.

---
Telling you what you are is "whining"?
---

For instance, was that crack about Phil necessary?

He shrieks and curses at everybody. Everybody. He deserves no respect,
and has demonstrated that it doesn't help. And his expertise stops at
20 KHz. Best thing to do is laugh at him, which at least makes him
useful.

---
The question was posed, not to elicit a rant, but to point out your
use of gratuitous insult as a debating trick.

Of course the answer is: "No, the crack wasn't necessary." but
answering truthfully would have put you on the defensive and we
certainly can't allow that to happen, can we?

In addition, he described how he used a signal generator, a scope, and
a length of coax to detect a suckout at the generator end of the cable
at about 27MHz, so you're wrong about his expertise by almost 5 orders
of magnitude, which _is_ laughable!

You really should either pay more attention to what you read or stop
propagating lies.

And who in the hell are you to judge who deserves respect and who
doesn't?
---

Of course not, and
all it can do is increase the enmity around here, which you seem wont
to do in an effort to belittle everyone else and exalt yourself, just
like Sloman does.

Don't be silly. I'm friendly and helpful to anybody who is reasonably
sincere,

---
Hogwash.

You're friendly and helpful to anyone who doesn't disagree with you,
and even then, only if they don't call you on your foibles.
---

and have made several personal in-the-flesh friends from
s.e.d. I post schematics. I send people parts. I'm polite to anyone
who is polite. Usenet does have an infinite supply of anonymous jerks,
and there's no reason to be polite to them.

---
I guess you've run out of cheeks, huh?
---

YOU escalate after you post stuff that's wrong, which you do fairly
often. My earlier posts about the "standing wave" thing were factual.
If, at that point, you had checked your claims, you might have avoided
a dispute, and maybe learned something to boot. You and Phil jumped on
me when you should have been thinking.

---
I can't speak for Phil, but I'll give you that one.
---

As far as the SWR thing goes, I went to the trouble of simulating it
to determine what the truth of the matter was, and accepted the result
which proved you were right.

*AFTER* making silly and insulting statements.

---
So what?

I ran the sim, proved myself wrong, and admitted it.
---

I'm usually right because I post about stuff I know (I live
transmission lines) and because I'm (usually) careful.

---
But when you're wrong you certainly don't own up to it.

For example, you pooh-poohed my statement that a 50 ohm attenuator
won't read accurately when driving anything other than a 50 ohm
resistive load.

Was I right or not?
---

Had you been wrong though, you'd still be dancing around looking for a
"What I meant was..." loophole to crawl through and generally blowing
a lot of smoke around in order to try to create confusion.

No. When I'm wrong I correct myself.

---
When _you_ find out you're wrong, perhaps; but whenever anyone _here_
finds you wrong you'll try a million ways to try to get out of it,
even when the mistake is as plain as the nose on your face.
---

It's no big deal top make a mistake occasionally.

---
Agreed.
---

When we actually lay out boards in my shop, we
design review and crosscheck exhaustively; I don't do that in
newsgroups, so of course I make the occasional mistake.

---
Yes, we all know that, but the point is that when you make a mistake
here you try to hide it instead of freely admitting to it and getting
on with your life.
---

Electronics is complex, and newsgroups don't matter.

---
Because one is true doesn't mean the other one is also.

Newsgroups _do_ matter.

Didn't you just finish saying you made some RL friends from USENET?

Do you consider that unimportant?

How about all the help you've been able to give people because of
USENET?

Is that also unimportant?
---

We all make mistakes, but you seem to be on a crusade bent on having
yours be seen as trivial, no matter how serious, and ours serious, no
matter how trivial.

I pointed out, in this case, that the OP would not see the effects of
standing waves at his scope input. No peaks, dips, mountain ranges.
The OP was being misled, lied to almost, and that was not trivial.

---
I wasn't talking about in this instance, I was talking about your
general demeanor.

In this instance, "Misled" implies a deliberate attempt to lead in a
wrong direction or into a mistaken action or belief, and "lied to
almost" strengthens that implication.

Since the mistake was honest, on my part, and I'm sure on Phil's as
well, it seems you're trying to deliberately mislead everyone into
believing that there was no error at all, but rather a contrived
effort to mislead. Shame on you.
---

And I thought you plonked me.

John

---
I did, but then I remembered Edmund Burke's:

"All that is necessary for the triumph of evil is for good men to do
nothing."

and I decided that you bear watching.

---
JF

 

[m II]

On 10-12-14 12:30 PM, John Fields wrote:

And I thought you plonked me.

John

---
I did, but then I remembered Edmund Burke's:

"All that is necessary for the triumph of evil is for good men to do
nothing."

Thanks for the heads up, John...and to think my sister was about to go
out with him...one shudders just thinking of what could have happened.



mike

 

[John Larkin]

On Tue, 14 Dec 2010 13:30:37 -0600, John Fields
<jfields@austininstruments.com> wrote:

On Tue, 14 Dec 2010 08:36:05 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 14 Dec 2010 07:03:37 -0600, John Fields
jfields@austininstruments.com> wrote:

On Mon, 13 Dec 2010 19:57:43 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 13 Dec 2010 19:46:03 -0600, John Fields
jfields@austininstruments.com> wrote:

I'm usually careful about what I post, and I count my P's and Q's, and
I mostly show my work so my thinking can be followed and any errors I
may make can be critiqued on that basis.

Kinda like peer review.

You, on the other hand, are dishonest in that you use subterfuge to
downplay your errors and you like to play fast and loose, so that when
anyone catches you in a technical error you use that looseness to
evade owning up to your errors and, instead, try to make it seem like
something was wrong with whoever caught your error.

What error did I make here? I predicted the frequency response the OP
would see, with the coax driving a hi-z scope input. I predicted he'd
see no frequency peaks or dips at the scope, just flat with a corner
around 200 MHz, and a 6 db/octave rolloff after that. Basic stuff,
actually.

You and Mr Personality predicted mountain ranges of peaks and dips
caused by standing waves.

You sim'd it and I was right. So why are you mad at me?

---
I'm not mad at you, I just don't like you.

Why? Basically, because you're nasty and sneaky when you don't get
your way or are found to be in error, and generally just
mean-spirited.

This is a public forum. Play the game or whine.

---
Telling you what you are is "whining"?
---

For instance, was that crack about Phil necessary?

He shrieks and curses at everybody. Everybody. He deserves no respect,
and has demonstrated that it doesn't help. And his expertise stops at
20 KHz. Best thing to do is laugh at him, which at least makes him
useful.

---
The question was posed, not to elicit a rant, but to point out your
use of gratuitous insult as a debating trick.

Of course the answer is: "No, the crack wasn't necessary." but
answering truthfully would have put you on the defensive and we
certainly can't allow that to happen, can we?

In addition, he described how he used a signal generator, a scope, and
a length of coax to detect a suckout at the generator end of the cable
at about 27MHz, so you're wrong about his expertise by almost 5 orders
of magnitude, which _is_ laughable!

You really should either pay more attention to what you read or stop
propagating lies.

And who in the hell are you to judge who deserves respect and who
doesn't?
---

Of course not, and
all it can do is increase the enmity around here, which you seem wont
to do in an effort to belittle everyone else and exalt yourself, just
like Sloman does.

Don't be silly. I'm friendly and helpful to anybody who is reasonably
sincere,

---
Hogwash.

You're friendly and helpful to anyone who doesn't disagree with you,
and even then, only if they don't call you on your foibles.
---

and have made several personal in-the-flesh friends from
s.e.d. I post schematics. I send people parts. I'm polite to anyone
who is polite. Usenet does have an infinite supply of anonymous jerks,
and there's no reason to be polite to them.

---
I guess you've run out of cheeks, huh?
---

YOU escalate after you post stuff that's wrong, which you do fairly
often. My earlier posts about the "standing wave" thing were factual.
If, at that point, you had checked your claims, you might have avoided
a dispute, and maybe learned something to boot. You and Phil jumped on
me when you should have been thinking.

---
I can't speak for Phil, but I'll give you that one.
---

As far as the SWR thing goes, I went to the trouble of simulating it
to determine what the truth of the matter was, and accepted the result
which proved you were right.

*AFTER* making silly and insulting statements.

---
So what?

I ran the sim, proved myself wrong, and admitted it.
---

I'm usually right because I post about stuff I know (I live
transmission lines) and because I'm (usually) careful.

---
But when you're wrong you certainly don't own up to it.

For example, you pooh-poohed my statement that a 50 ohm attenuator
won't read accurately when driving anything other than a 50 ohm
resistive load.

I don't know what you mean by "read accurately." Attenuators add a
calibrated loss in a specified environment.

Assume a 50 ohm generator driving some arbitrary load. Measure the
voltage at the load. Now insert a 20 dB 50-ohm attenuator. The voltage
at that same load drops by 10:1, namely 20 dB. The attenuator did what
it was advertised to do, drop the signal level by 20 dB. That works
for any linear load, any load impedance.

You probably need to Spice that one, too.

Was I right or not?

I don't really know what your point was. A 50 ohm attenuator, driving
a 50 ohm cable, works just like the same attenuator with no cable. The
cable only adds time delay.

---

Had you been wrong though, you'd still be dancing around looking for a
"What I meant was..." loophole to crawl through and generally blowing
a lot of smoke around in order to try to create confusion.

No. When I'm wrong I correct myself.

---
When _you_ find out you're wrong, perhaps; but whenever anyone _here_
finds you wrong you'll try a million ways to try to get out of it,
even when the mistake is as plain as the nose on your face.

Countercase, recent, in s.e.d.

John

skipping the rest

 

[John Larkin]

On Tue, 14 Dec 2010 13:20:06 -0700, m II <C@in.the.hat> wrote:

On 10-12-14 12:30 PM, John Fields wrote:

And I thought you plonked me.

John

---
I did, but then I remembered Edmund Burke's:

"All that is necessary for the triumph of evil is for good men to do
nothing."


Thanks for the heads up, John...and to think my sister was about to go
out with him...one shudders just thinking of what could have happened.



mike

Ooh, you could have been uncle to a tiny Fieldslet.

John

 

[John Fields]

On Tue, 14 Dec 2010 13:20:06 -0700, m II <C@in.the.hat> wrote:

On 10-12-14 12:30 PM, John Fields wrote:

And I thought you plonked me.

John

---
I did, but then I remembered Edmund Burke's:

"All that is necessary for the triumph of evil is for good men to do
nothing."


Thanks for the heads up, John...and to think my sister was about to go
out with him...one shudders just thinking of what could have happened.

---
Ah, a breath of fresh air in this stiflingly confrontational arena!

Thanks for the chuckle.

---
JF

 

[John Fields]

On Tue, 14 Dec 2010 13:50:49 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 14 Dec 2010 13:30:37 -0600, John Fields
jfields@austininstruments.com> wrote:


But when you're wrong you certainly don't own up to it.

For example, you pooh-poohed my statement that a 50 ohm attenuator
won't read accurately when driving anything other than a 50 ohm
resistive load.

I don't know what you mean by "read accurately." Attenuators add a
calibrated loss in a specified environment.

---
Indeed, and if the load impedance is different from that specified,
then the environment will have changed and the loss will be different
from what was predicted for the specified environment.
---

Assume a 50 ohm generator driving some arbitrary load.

---
The load can't be arbitrary if the environment is specified, so your
argument is specious from the start.
---

Measure the voltage at the load. Now insert a 20 dB 50-ohm attenuator.

The voltage at that same load drops by 10:1, namely 20 dB.

The attenuator did what it was advertised to do, drop the signal level by 20 dB.

That works for any linear load, any load impedance.

---
What you're trying to skirt, by specifying that the voltage be
measured at the load, is that the voltage _can't_ be measured at the
load from the generator's point of view, and must be predicted based
upon the environment specified.

Therefore, if the transmission line impedance or the load impedance is
different from that specified, the value of attenuation displayed by
the generator's attenuator won't be right.
---

You probably need to Spice that one, too.

---
I already have, so I _know_ you're wrong.

Why don't you Spice it yourself and post what you find?

---
JF

 

[John Fields]

On Tue, 14 Dec 2010 13:52:15 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 14 Dec 2010 13:20:06 -0700, m II <C@in.the.hat> wrote:

On 10-12-14 12:30 PM, John Fields wrote:

And I thought you plonked me.

John

---
I did, but then I remembered Edmund Burke's:

"All that is necessary for the triumph of evil is for good men to do
nothing."


Thanks for the heads up, John...and to think my sister was about to go
out with him...one shudders just thinking of what could have happened.



mike

Ooh, you could have been uncle to a tiny Fieldslet.

John

---
Where'd you get that from unless you think I'd be acting through you,
ugh, and wanted to foster a pervert child?

---
JF

 

[Rich Grise]

John Fields wrote:

On Tue, 14 Dec 2010 13:52:15 -0800, John Larkin
On Tue, 14 Dec 2010 13:20:06 -0700, m II <C@in.the.hat> wrote:

Thanks for the heads up, John...and to think my sister was about to go
out with him...one shudders just thinking of what could have happened.

Ooh, you could have been uncle to a tiny Fieldslet.
---
Where'd you get that from unless you think I'd be acting through you,
ugh, and wanted to foster a pervert child?

Could you guys please take the pissfest to some group other than s.e.basics?

You're frightening the newbies.

Thanks,
Rich

 

[John Larkin]

On Tue, 14 Dec 2010 16:41:16 -0800, Rich Grise
<richg@example.net.invalid> wrote:

John Fields wrote:
On Tue, 14 Dec 2010 13:52:15 -0800, John Larkin
On Tue, 14 Dec 2010 13:20:06 -0700, m II <C@in.the.hat> wrote:

Thanks for the heads up, John...and to think my sister was about to go
out with him...one shudders just thinking of what could have happened.

Ooh, you could have been uncle to a tiny Fieldslet.
---
Where'd you get that from unless you think I'd be acting through you,
ugh, and wanted to foster a pervert child?

Could you guys please take the pissfest to some group other than s.e.basics?

You're frightening the newbies.

They should learn a little something about transmission lines and
attenuators. JF should, too.

John

 

If it's terminated at either end, or at both ends, the cable length
won't matter. Very long coax runs can degrade rise/fall times, but a
few feet of RG58 won't have any noticable effect at risetimes of, say,
1 ns.

You'll need a fast scope, 200 MHz at the very least, to measure a 3.5
ns wide pulse. 500 MHz would be better.

John

That is why I save my 500 Mhz Old Tek scope for things like that


We have one working 7104 (1 GHz, analog, microchannel plate) scope we
use occasionally. All our other analog scopes are retired.

We have a bunch of Tek 11801 sampling scopes, with sampling heads that
range from 3 GHz to 40 GHz. They are fairly cheap on ebay these days.

John
I'm obviously going to need one. I'm not giving up on this. I love the

project ( photomultiplier with scintillator) and have investeted in
the ortec equipment , its just that the counter isn't registeing
anything so I wanted a view of the pulse. I'll try Mr. Larkins
suggestion of taking the pulse off a 50 term coax and feeding that to
the pulse shaper. It coulld be the parasitic preamp. Yes , I'm
certainly a babe in the woods, jk

 

[Phil Allison]

jfisher864@comcast.net

Yes , I'm certainly a babe in the woods,

jk

** Babes in the woods should always make sure they CAN see the forest
through all those damn trees ....





..... Phil

 

On Wed, 15 Dec 2010 12:53:58 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

jfisher864@comcast.net

Yes , I'm certainly a babe in the woods,

jk


** Babes in the woods should always make sure they CAN see the forest
through all those damn trees ....

Yes and any time you would like to have a discussion of Lie Algebra

I'm here. We all have something were good at. Don't get to full of
youself. Stay humble jk

 

[Phil Allison]

<jfisher864@comcast.net>

"Phil Allison"

Yes , I'm certainly a babe in the woods,

jk


** Babes in the woods should always make sure they CAN see the forest
through all those damn trees ....

Yes and any time you would like to have a discussion of Lie Algebra
I'm here.

** Wot an autistic fuckwit.

We all have something were good at.

** And should therefore stick exclusively too.



..... Phil

 

[John Larkin]

On Tue, 14 Dec 2010 17:47:47 -0600, John Fields
<jfields@austininstruments.com> wrote:

On Tue, 14 Dec 2010 13:50:49 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 14 Dec 2010 13:30:37 -0600, John Fields
jfields@austininstruments.com> wrote:


But when you're wrong you certainly don't own up to it.

For example, you pooh-poohed my statement that a 50 ohm attenuator
won't read accurately when driving anything other than a 50 ohm
resistive load.

I don't know what you mean by "read accurately." Attenuators add a
calibrated loss in a specified environment.

---
Indeed, and if the load impedance is different from that specified,
then the environment will have changed and the loss will be different
from what was predicted for the specified environment.
---

Assume a 50 ohm generator driving some arbitrary load.

---
The load can't be arbitrary if the environment is specified, so your
argument is specious from the start.

"Arbitrary" means "any".

---

Measure the voltage at the load. Now insert a 20 dB 50-ohm attenuator.

The voltage at that same load drops by 10:1, namely 20 dB.

The attenuator did what it was advertised to do, drop the signal level by 20 dB.

That works for any linear load, any load impedance.

---
What you're trying to skirt, by specifying that the voltage be
measured at the load, is that the voltage _can't_ be measured at the
load from the generator's point of view, and must be predicted based
upon the environment specified.

You can't afford a scope, or a voltmeter?

Therefore, if the transmission line impedance or the load impedance is
different from that specified, the value of attenuation displayed by
the generator's attenuator won't be right.

Maybe you got a bad attenuator. All of mine do what I described.

Hey, here's the guts of a VAT-20:

ftp://jjlarkin.lmi.net/VAT-20.zip

Thickfilms, only good to 6 GHz. I wonder what that gold dot in the
middle is all about.

John