signal generator output

On Wed, 15 Dec 2010 14:22:17 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

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
Gracias I do appreciate your proffesional comments, regarding

electronics . By the way ,if your so intellleigent ,why hang out at
electronics basics? This is a place for people to learn, it kind of
reminds me of a 100 kg bully on the kindergarten. playground.
Can't you hold your own on a more advanced newsgroup?????

 

[Phil Allison]

<jfisher864@comcast.net

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

jerk


** 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.


Gracias I do appreciate your proffesional comments,

** Wot a fucking NARCISSISTIC ASSHOLE you are.

My comment about babes, woods and trees was a * simple joke *

- you pathetic jerkoff !!!!!!!!!!!!

By the way ,if your so intellleigent ,why hang out at
electronics basics?

** Your question was out of line here.

Your vile attitude is WAY out of line anywhere.

Go get a life or go drop dead.

Learn to spell too.



...... Phil

 

[JW]

On Sat, 11 Dec 2010 08:34:56 -0800 John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in Message id:
<kl97g6httssb7suedijmu1a2oof2nrcafd@4ax.com>:

Function generators are usually
spec'd/calibrated to deliver some voltage into an open circuit. The
difference is 2:1 voltage.

That could be true, but not the ones I've played with, although it's a
pretty short list. 8116A and 33120A generators are calibrated at 50 ohm
impedance.

 

[John Fields]

On Tue, 14 Dec 2010 19:57:28 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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".

---
Yes, I know what "arbitrary" means, and I also know what "moving the
goalpost" means, and it seems that's precisely what you're trying to
do.


Here; let's see if we can't tighten thing up a little:

In order for a signal generator to operate as specified, the condtions
under which it's supposed to work have to be specified, and those
conditions are usually that the impedances of the generator, the
transmission line, and the load all be equal and that all reactances
cancel.

Let's say we have a variable frequency signal generator, with a 50 ohm
resistive output impedance, which sports a variable attenuator.

Now, let's say that we connect one end of a coaxial cable with a
characteristic impedance of 50 ohms to the generator, and connect the
other end of the cable to a 50 ohm resistive load. OK so far?

Now we set the frequency to some arbitrary value and the attenuator
to, say, 0dBm, all without measuring anything at either end of the
cable.

To check the attenuator, though, we measure the voltage across the
load and we get 632 millivolts, peak to peak, which is just what we
expected.

Now, remove the 50 ohm load, replace it with a 15pF capacitor, and
measure the voltage across the cap. Will it be 632 millivolts, peak
to peak?

Only at one frequency, so it's not likely, which means that the
attenuator's 0dBm setting is meaningless. In other words, it's not
reading accurately, particularly because the load is mostly reactive
and is dissipating only a miniscule amount of power.


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TEXT -784 312 Left 0 !.tran 1e-7


Snipped some buffoonery...
---

---
JF

 

[JW]

On Tue, 14 Dec 2010 19:40:45 -0600 jfisher864@comcast.net wrote in Message
id: <mn6gg6dbf8n38hihj715k9fvj9vaarfgsj@4ax.com>:

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

Any interest in a 54522A? It's a two channel 500MHz 2GSa/s scope. Some
screen burn, but display is still nice and bright. I'd sell it for $750 +
shipping with a 30 day warranty.

You can see it on Ebay item 190384647489
I do the repair work for the guy, and this scope he's selling is mine.
(In fact just about all his scopes for sale are mine.)

 

[John Larkin]

On Wed, 15 Dec 2010 07:45:58 -0600, John Fields
<jfields@austininstruments.com> wrote:

On Tue, 14 Dec 2010 19:57:28 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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".

---
Yes, I know what "arbitrary" means, and I also know what "moving the
goalpost" means, and it seems that's precisely what you're trying to
do.

What I did was state that a 20 dB attenuator, after a 50 ohm source,
introduces 20 dB of attenuation no matter what the load impedance.

Here; let's see if we can't tighten thing up a little:

In order for a signal generator to operate as specified, the condtions
under which it's supposed to work have to be specified, and those
conditions are usually that the impedances of the generator, the
transmission line, and the load all be equal and that all reactances
cancel.

Let's say we have a variable frequency signal generator, with a 50 ohm
resistive output impedance, which sports a variable attenuator.

Now, let's say that we connect one end of a coaxial cable with a
characteristic impedance of 50 ohms to the generator, and connect the
other end of the cable to a 50 ohm resistive load. OK so far?

Now we set the frequency to some arbitrary value and the attenuator
to, say, 0dBm, all without measuring anything at either end of the
cable.

Technically, an attenuator is set to some number of dBs, not dBm's.
But ok...

To check the attenuator, though, we measure the voltage across the
load and we get 632 millivolts, peak to peak, which is just what we
expected.

Now, remove the 50 ohm load, replace it with a 15pF capacitor, and
measure the voltage across the cap. Will it be 632 millivolts, peak
to peak?

It's a 50 ohm source. It makes a voltage divider with any impedance
you connect to it. That's exactly the answer to the OPs original
question. Why make it complex?

John

Only at one frequency, so it's not likely, which means that the
attenuator's 0dBm setting is meaningless. In other words, it's not
reading accurately, particularly because the load is mostly reactive
and is dissipating only a miniscule amount of power.


Version 4
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WIRE -784 128 -816 128
WIRE -640 128 -704 128
WIRE -464 128 -544 128
WIRE -224 128 -304 128
WIRE -64 128 -128 128
WIRE 48 128 16 128
WIRE -640 160 -672 160
WIRE -512 160 -544 160
WIRE -224 160 -256 160
WIRE -96 160 -128 160
WIRE -816 176 -816 128
WIRE -464 176 -464 128
WIRE -304 176 -304 128
WIRE 48 176 48 128
WIRE -816 288 -816 256
WIRE -672 288 -672 160
WIRE -672 288 -816 288
WIRE -512 288 -512 160
WIRE -512 288 -672 288
WIRE -464 288 -464 256
WIRE -464 288 -512 288
WIRE -304 288 -304 240
WIRE -304 288 -464 288
WIRE -256 288 -256 160
WIRE -256 288 -304 288
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WIRE -96 288 -256 288
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SYMATTR Value2 AC 1
TEXT -792 344 Left 0 !;ac oct 255 10e6 1000e6
TEXT -784 312 Left 0 !.tran 1e-7


Snipped some buffoonery...
---

---
JF

 

[John Fields]

On Wed, 15 Dec 2010 07:14:40 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 15 Dec 2010 07:45:58 -0600, John Fields
jfields@austininstruments.com> wrote:

On Tue, 14 Dec 2010 19:57:28 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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".

---
Yes, I know what "arbitrary" means, and I also know what "moving the
goalpost" means, and it seems that's precisely what you're trying to
do.


What I did was state that a 20 dB attenuator, after a 50 ohm source,
introduces 20 dB of attenuation no matter what the load impedance.

---
Yeah, but it was irrelevant in context; just more of your smoke and
mirrors.


here's the original "dicourse":

<QUOTE>

A good signal generator should be a 50 ohm source at all frequencies.

John

---
Yes, of course.

We all know that, but a signal generator with an attenuator designed
and legended to drive a resistive load will only be accurate at the
frequency where the capacitor's reactance is such that the voltage
across it will be half that of the open-circuit voltage of the
generator.

Gibberish.

And, even at that, the attenuator will only be useful in determining
the voltage across the load, not the power into it, as displayed,
since the load is reactive.

Ditto.

John
<END Quote>

Why Gibberish?
---

Here; let's see if we can't tighten thing up a little:

In order for a signal generator to operate as specified, the condtions
under which it's supposed to work have to be specified, and those
conditions are usually that the impedances of the generator, the
transmission line, and the load all be equal and that all reactances
cancel.

Let's say we have a variable frequency signal generator, with a 50 ohm
resistive output impedance, which sports a variable attenuator.

Now, let's say that we connect one end of a coaxial cable with a
characteristic impedance of 50 ohms to the generator, and connect the
other end of the cable to a 50 ohm resistive load. OK so far?

Now we set the frequency to some arbitrary value and the attenuator
to, say, 0dBm, all without measuring anything at either end of the
cable.

Technically, an attenuator is set to some number of dBs, not dBm's.
But ok...


To check the attenuator, though, we measure the voltage across the
load and we get 632 millivolts, peak to peak, which is just what we
expected.

Now, remove the 50 ohm load, replace it with a 15pF capacitor, and
measure the voltage across the cap. Will it be 632 millivolts, peak
to peak?

It's a 50 ohm source. It makes a voltage divider with any impedance
you connect to it.

---
But, unless the line and load are matched to it, the attenuator
setting on the generator will be meaningless.

And you seem to be ducking the question, which is:

Now, remove the 50 ohm load, replace it with a 15pF capacitor, and
measure the voltage across the cap. Will it be 632 millivolts, peak
to peak?

---
JF

 

[John Larkin]

On Wed, 15 Dec 2010 11:24:27 -0600, John Fields
<jfields@austininstruments.com> wrote:

On Wed, 15 Dec 2010 07:14:40 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Wed, 15 Dec 2010 07:45:58 -0600, John Fields
jfields@austininstruments.com> wrote:

On Tue, 14 Dec 2010 19:57:28 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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".

---
Yes, I know what "arbitrary" means, and I also know what "moving the
goalpost" means, and it seems that's precisely what you're trying to
do.


What I did was state that a 20 dB attenuator, after a 50 ohm source,
introduces 20 dB of attenuation no matter what the load impedance.

---
Yeah, but it was irrelevant in context; just more of your smoke and
mirrors.


here's the original "dicourse":

QUOTE
A good signal generator should be a 50 ohm source at all frequencies.

John

---
Yes, of course.

We all know that, but a signal generator with an attenuator designed
and legended to drive a resistive load will only be accurate at the
frequency where the capacitor's reactance is such that the voltage
across it will be half that of the open-circuit voltage of the
generator.

Gibberish.


And, even at that, the attenuator will only be useful in determining
the voltage across the load, not the power into it, as displayed,
since the load is reactive.

Ditto.

John
END Quote

Why Gibberish?
---

Here; let's see if we can't tighten thing up a little:

In order for a signal generator to operate as specified, the condtions
under which it's supposed to work have to be specified, and those
conditions are usually that the impedances of the generator, the
transmission line, and the load all be equal and that all reactances
cancel.

Let's say we have a variable frequency signal generator, with a 50 ohm
resistive output impedance, which sports a variable attenuator.

Now, let's say that we connect one end of a coaxial cable with a
characteristic impedance of 50 ohms to the generator, and connect the
other end of the cable to a 50 ohm resistive load. OK so far?

Now we set the frequency to some arbitrary value and the attenuator
to, say, 0dBm, all without measuring anything at either end of the
cable.

Technically, an attenuator is set to some number of dBs, not dBm's.
But ok...


To check the attenuator, though, we measure the voltage across the
load and we get 632 millivolts, peak to peak, which is just what we
expected.

Now, remove the 50 ohm load, replace it with a 15pF capacitor, and
measure the voltage across the cap. Will it be 632 millivolts, peak
to peak?

It's a 50 ohm source. It makes a voltage divider with any impedance
you connect to it.

---
But, unless the line and load are matched to it, the attenuator
setting on the generator will be meaningless.

Not at all. You just have to apply any corrections as needed. Into a
Hi-Z load, the output voltage is 2x compared to driving a 50 ohm load.
It's just a voltage divider. Any reasonable amount of 50r coax between
the generator and the load has no effect.

The OP needed exactly that 2x correction. Or a termination.

And you seem to be ducking the question, which is:

Now, remove the 50 ohm load, replace it with a 15pF capacitor, and
measure the voltage across the cap. Will it be 632 millivolts, peak
to peak?

---
JF

I explained the OP's situation long ago: RF generators are usually
calibrated assuming a 50 ohm load, and his load is a small
capacitance. You and Phil explained the error in terms of standing
waves, with Himilayan mountains of dips and peaks, which is wrong. His
voltage is twice what he expected because he has a hi-Z load. It's a
simple case of a 50 ohm source making more voltage unloaded than it
does loaded. It's just a voltage divider.

As noted, that was settled long ago. It's bog simple. Why you want to
keep clucking about it, I can't imagine.

I also noted that function (not RF) generators are usually specified,
for output voltage, unloaded. The ones I sell sure are. We usually
seed a lot of notes into our specs (like "+-10 volts max, +-5 max into
50 ohms") in lots of places, because many people don't understand
this.

John

 

[George Herold]

On Dec 14, 8:40 pm, jfisher...@comcast.net wrote:

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- Hide quoted text -

- Show quoted text -

If you've got a 50 MHz 'scope that may be enough to see your PMT
pulses. There will be some broadening of the pulse, but still
visible. I assume there is a discriminator in part of your ortec
equiment? (comparator with variable refernce level) That should be
all you need to get some nice big pulses for your counter.

George H.

 

[John Larkin]

On Tue, 14 Dec 2010 19:40:45 -0600, jfisher864@comcast.net wrote:

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

The equivalent-time sampling scopes are fast, but not useful for
looking at PMT pulses. They need repetitive waveforms.

Even a 100 MHz scope (3.5 ns risetime) should be OK for a typical
PMT/scintillator.

John

 

[John Larkin]

On Wed, 15 Dec 2010 08:42:57 -0500, JW <none@dev.null> wrote:

On Sat, 11 Dec 2010 08:34:56 -0800 John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in Message id:
kl97g6httssb7suedijmu1a2oof2nrcafd@4ax.com>:

Function generators are usually
spec'd/calibrated to deliver some voltage into an open circuit. The
difference is 2:1 voltage.

That could be true, but not the ones I've played with, although it's a
pretty short list. 8116A and 33120A generators are calibrated at 50 ohm
impedance.

It could go either way; you've got to read the specs and adjust.

John

 

On Wed, 15 Dec 2010 17:42:32 +1100, "Phil Allison" <phil_a@tpg.com.au>
wrote:

jfisher864@comcast.net

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

jerk


** 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.


Gracias I do appreciate your proffesional comments,


** Wot a fucking NARCISSISTIC ASSHOLE you are.

My comment about babes, woods and trees was a * simple joke *

- you pathetic jerkoff !!!!!!!!!!!!

From my side it was an insult, maybe leave a marker that you're
joking next time. You're a real comedian.

By the way ,if your so intellleigent ,why hang out at
electronics basics?


** Your question was out of line here.

Gee sorry I hurt your feelings.

Your vile attitude is WAY out of line anywhere.

Go get a life or go drop dead.

Learn to spell too.



..... Phil

My questions were answered by all those who responded , you,I can do
without. On to the next topic.....

 

[Phil Allison]

<jfisher864@comcast.net = another dime a dozen autistic fuckwit

** 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.


Gracias I do appreciate your proffesional comments,


** Wot a fucking NARCISSISTIC ASSHOLE you are.

My comment about babes, woods and trees was a * simple joke *

- you pathetic jerkoff !!!!!!!!!!!!

From my side it was an insult,

** From your side of what - exactly ??

The Twilight Zone ????

The local Psychiatric ward ??

( snip abuse)

By the way ,if your so intellleigent ,why hang out at
electronics basics?

Your question was way out of line here.

Your vile attitude is WAY out of line anywhere.

Go get a life or go drop fucking dead.




..... Phil