215 ohms?

A

A E

Guest
What uses 215 ohm impedance?
Going through my new desk at work I came across an otherwise unmarked scope
probe that reads "215 ohms 1:1".
No one else seems to know what it's for either. It's manufactured, not home
made.
Any thoughts?
Thanks,
Alex
 
A E wrote:
What uses 215 ohm impedance?
Going through my new desk at work I came across an otherwise unmarked scope
probe that reads "215 ohms 1:1".
No one else seems to know what it's for either. It's manufactured, not home
made.
Any thoughts?
Thanks,
Alex
Click to expand...
Take your ohm-meter and measure from tip to center pin
of the bnc. What do you get?
mike

--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
4in/400Wout ham linear amp.
Honda CB-125S
400cc Dirt Bike 2003 miles $550
Police Scanner, Color LCD overhead projector
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
:
Click to expand...
: Take your ohm-meter and measure from tip to center pin
: of the bnc. What do you get?
: mike
:

That will not work, try it with 50 & 75 Ohm coax cable.
 
Eric wrote:
:
: Take your ohm-meter and measure from tip to center pin
: of the bnc. What do you get?
: mike
:

That will not work, try it with 50 & 75 Ohm coax cable.
Click to expand...
ExcUUUUUUUUse me???
What about hooking two ohm-meter leads to two points on a cable
and reporting the result "will not work"? I'm sticking my neck out and
will guarantee
that if you stick one lead on the probe tip and the other on the
center of the bnc, you WILL get a reading somewhere between
zero and infinity ohms. What's the number?
mike

--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
4in/400Wout ham linear amp.
Honda CB-125S
400cc Dirt Bike 2003 miles $550
Police Scanner, Color LCD overhead projector
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
In article <3F8153DA.1090301@juno.com>, mike <spamme0@juno.com> wrote:

ExcUUUUUUUUse me???
What about hooking two ohm-meter leads to two points on a cable
and reporting the result "will not work"? I'm sticking my neck out and
will guarantee
that if you stick one lead on the probe tip and the other on the
center of the bnc, you WILL get a reading somewhere between
zero and infinity ohms. What's the number?
Click to expand...
If the coax isn't shorted somewhere inside, then a standard DC
ohmmeter reading of the center-conductor-to-braid resistance will be
as close to infinity as matters. If the ohmmeter doesn't read nearly
infinite, it's due to leakage somewhere (even fingertip contact with
the probes or coax conductors could pull the reading down to a few
megohms).

Whatever reading comes out of the ohmmeter, will have _no_
relationship at all to the cable's characteristic (or surge)
impedance. 50-ohm cable such as RG-58, 75-ohm such as RG-59, 93-ohm,
150-ohm cable... they'll *all* read nearly infinite DC resistance from
center conductor to braid/shield.

The characteristic impedance can be measured only using radio
frequency techniques, TDR or similar impulse measurements, etc. You
simply cannot determine it using a DC ohmmeter.

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
 
dplatt@radagast.org (Dave Platt) wrote:
mike <spamme0@juno.com> wrote:
that if you stick one lead on the probe tip and the other on the
center of the bnc, you WILL get a reading somewhere between

If the coax isn't shorted somewhere inside, then a standard DC
ohmmeter reading of the center-conductor-to-braid resistance will be
as close to infinity as matters.
Click to expand...
I wonder if Mike is asking for a DC measurement to see if there's some
kind of resistive divider in the probe. You might also want to
measure across the input and between the coax on the input and output
sides to see if there's some kind of network in there...

--
William Smith w<underscore>smith@compusmiths.com
ComputerSmiths Consulting, Inc. www.compusmiths.com
 
Dave Platt wrote:
In article <3F8153DA.1090301@juno.com>, mike <spamme0@juno.com> wrote:


ExcUUUUUUUUse me???
What about hooking two ohm-meter leads to two points on a cable
and reporting the result "will not work"? I'm sticking my neck out and
will guarantee
that if you stick one lead on the probe tip and the other on the
center of the bnc, you WILL get a reading somewhere between
zero and infinity ohms. What's the number?


If the coax isn't shorted somewhere inside, then a standard DC
ohmmeter reading of the center-conductor-to-braid resistance will be
as close to infinity as matters.
Click to expand...
Except that I said from probe tip to bnc center conductor. Nowhere did
I mention braid, shield, ground or any other terminal.

If the ohmmeter doesn't read nearly
infinite, it's due to leakage somewhere (even fingertip contact with
the probes or coax conductors could pull the reading down to a few
megohms).

Whatever reading comes out of the ohmmeter, will have _no_
relationship at all to the cable's characteristic (or surge)
impedance. 50-ohm cable such as RG-58, 75-ohm such as RG-59, 93-ohm,
150-ohm cable... they'll *all* read nearly infinite DC resistance from
center conductor to braid/shield.
Click to expand...
There you go with that braid again.

The characteristic impedance
Click to expand...
I never mentioned characteristic impedance either...

can be measured only using radio
frequency techniques, TDR or similar impulse measurements, etc. You
simply cannot determine it using a DC ohmmeter.
Click to expand...
Pet Peeve Alert:
I love it when people chime in with authoritative statements about
issues well beyond their area of expertise. Seems the farther it gets
from the issues, the more people weigh in.

Let's review...
About all we actually KNOW is that the OP has some unknown 1X probe and
a question about a number.

In such instances, it's often tutorial to ask a well-formed question that
will provide additional data and maybe even lead the OP to a direct
answer to his question.

Then we get people (who apparently didn't read the question) jumping in
to say that the question is wrong and
proceeding to detail why some other question would have been wrong.

I don't have the Psychic Hotline on speed dial. I don't know anything
about the OP's probe. But I can give some general information.

Tutorial starts here:
It's difficult to get a signal into a 1 Meg scope input. Most probe
leads act like relatively low impedance transmission lines. It's not
possible to terminate them. 'bout all you can do is stick some
resistance in series to damp reflections. Turns out that it works a lot
better if you distribute the resistance along the transmission line.
Quality probes are made with special coaxial transmission line with
resistance wire for the center conductor.

So, if you were to make a resistance measurement from probe tip to the
center pin of the BNC, you just might measure some resistance. And if
that resistance were approximately the number in question, you might
have an answer to your question.

Flame suit on...take another shot from the hip.

mike

--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
4in/400Wout ham linear amp.
Honda CB-125S
400cc Dirt Bike 2003 miles $550
Police Scanner, Color LCD overhead projector
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
what we are trying to tell you Mike

it might have an impedance of 215 Ohms

But you can NOT measure it with DC current, no were will you find it with DC
current, full stop.










"mike" <spamme0@juno.com> wrote in message news:3F821B4D.2000304@juno.com...
: Dave Platt wrote:
: > In article <3F8153DA.1090301@juno.com>, mike <spamme0@juno.com> wrote:
: >
: >
: >>ExcUUUUUUUUse me???
: >>What about hooking two ohm-meter leads to two points on a cable
: >>and reporting the result "will not work"? I'm sticking my neck out and
: >>will guarantee
: >>that if you stick one lead on the probe tip and the other on the
: >>center of the bnc, you WILL get a reading somewhere between
: >>zero and infinity ohms. What's the number?
: >
: >
: > If the coax isn't shorted somewhere inside, then a standard DC
: > ohmmeter reading of the center-conductor-to-braid resistance will be
: > as close to infinity as matters.
:
: Except that I said from probe tip to bnc center conductor. Nowhere did
: I mention braid, shield, ground or any other terminal.
:
: If the ohmmeter doesn't read nearly
: > infinite, it's due to leakage somewhere (even fingertip contact with
: > the probes or coax conductors could pull the reading down to a few
: > megohms).
: >
: > Whatever reading comes out of the ohmmeter, will have _no_
: > relationship at all to the cable's characteristic (or surge)
: > impedance. 50-ohm cable such as RG-58, 75-ohm such as RG-59, 93-ohm,
: > 150-ohm cable... they'll *all* read nearly infinite DC resistance from
: > center conductor to braid/shield.
:
: There you go with that braid again.
:
: >
: > The characteristic impedance
:
: I never mentioned characteristic impedance either...
:
: can be measured only using radio
: > frequency techniques, TDR or similar impulse measurements, etc. You
: > simply cannot determine it using a DC ohmmeter.
:
: Pet Peeve Alert:
: I love it when people chime in with authoritative statements about
: issues well beyond their area of expertise. Seems the farther it gets
: from the issues, the more people weigh in.
:
: Let's review...
: About all we actually KNOW is that the OP has some unknown 1X probe and
: a question about a number.
:
: In such instances, it's often tutorial to ask a well-formed question that
: will provide additional data and maybe even lead the OP to a direct
: answer to his question.
:
: Then we get people (who apparently didn't read the question) jumping in
: to say that the question is wrong and
: proceeding to detail why some other question would have been wrong.
:
: I don't have the Psychic Hotline on speed dial. I don't know anything
: about the OP's probe. But I can give some general information.
:
: Tutorial starts here:
: It's difficult to get a signal into a 1 Meg scope input. Most probe
: leads act like relatively low impedance transmission lines. It's not
: possible to terminate them. 'bout all you can do is stick some
: resistance in series to damp reflections. Turns out that it works a lot
: better if you distribute the resistance along the transmission line.
: Quality probes are made with special coaxial transmission line with
: resistance wire for the center conductor.
:
: So, if you were to make a resistance measurement from probe tip to the
: center pin of the BNC, you just might measure some resistance. And if
: that resistance were approximately the number in question, you might
: have an answer to your question.
:
: Flame suit on...take another shot from the hip.
:
: mike
:
: --
: Bunch of stuff For Sale and Wanted at the link below.
: laptops and parts Test Equipment
: 4in/400Wout ham linear amp.
: Honda CB-125S
: 400cc Dirt Bike 2003 miles $550
: Police Scanner, Color LCD overhead projector
: Tek 2465 $800, ham radio, 30pS pulser
: Tektronix Concept Books, spot welding head...
: http://www.geocities.com/SiliconValley/Monitor/4710/
:
 
"Eric" <some1@clare.co.nz> wrote:
what we are trying to tell you Mike

it might have an impedance of 215 Ohms

But you can NOT measure it with DC current, no were will you find it with DC
current, full stop.
Click to expand...
I think what Mike is trying to suggest is that there may be a
resistive network inside the silly thing, and that by making a few DC
resistance measurements you might get some hints as to how the thing
is wired internally.

He seems to understand that the high frequency impedance of it can't
be measured with an ohmmeter, but many impedance matching networks are
made from resistive components, yes?

--
William Smith w<underscore>smith@compusmiths.com
ComputerSmiths Consulting, Inc. www.compusmiths.com
 
"William P.N. Smith smith@compusmiths.com>" <w<underscore> wrote in message
news:96r5ovgn8gk47ope8mkhvj2d7q8a1ic9qg@4ax.com...
"Eric" <some1@clare.co.nz> wrote:
what we are trying to tell you Mike [...]
Click to expand...

Hey, if we can quit wrangling over how to measure the impedance of a probe,
maybe we can get back to the OP's actual question - I'd love to know the
answer myself. That question was:

"What uses 215 ohm impedance?"

If s/he'd asked "what uses 75 ohm impedance" or "what uses 50 ohm impedance"
or "what uses 600 ohm impedance" I'd have some answers (no doubt answers
s/he already knows)... But I've never heard of a transmission system built
around 215 ohms.

Has anyone else?
 
Eric wrote:
what we are trying to tell you Mike
Click to expand...
I understand what you're trying to tell me. I'm denying it's
relevance to my suggestion that the OP measure the DC resistance of
the center conductor.

it might have an impedance of 215 Ohms
Click to expand...
Yes, it might. I have not done the math...
Typical probe shield inside diameter is 0.06". Center conductor is
..0025, but this is past the accuracy limit of my dial caliper.
I was too lazy to measure the dielectric constant, use 2.3 for poly.
Do the math.
Come back and tell us if
you still think the Zo might be 215 ohms.
Hint, the back of my envelope sez 126 ohms...so I guess now I HAVE done
the math.

And since I went to all the trouble of going up in the attic to fetch
some probe cable, I measured it. This particular stuff is 38 ohms/foot.
That's DC RESISTANCE OF THE CENTER CONDUCTOR.
NOTE THAT THIS IS NOT, NOT, NOT THE Zo...IT IS DC RESISTANCE!!!!!!!
MEASURED WITH AN OHM-METER, NOT A TDR!!!! OF THE CENTER CONDUCTOR,
NOT THE SHIELD, BRAID, OR ANY OTHER TERMINAL.
I DON'T KNOW HOW TO BE MORE CLEAR, SO I'LL JUST SAY IT LOUDER!!!!!
;-)

But you can NOT measure it with DC current, no were will you find it with DC
current, full stop.
Click to expand...
Stop as full as you want. I NEVER mentioned characteristic impedance
except to state that it was not relevant to MY suggestion that the OP
measure the damned DC resistance of the center conductor.

About three posts up this thread (and quoted below, so we know you read
it) I disclosed EXACTLY why one might want to measure
said DC resistance...yet you still tell me that the question that I
didn't ask is the wrong one.

So, after all this, if the OP had just answered the question I first
asked, he would have had the answer. Maybe 20 years designing
instrumentation for Tektronix...nah, dumb luck.

I just love the web. It entertains me for hours (in this case days) at
a time.
mike

Read
Read it again
Understand
Think
Think some more
Post

"mike" <spamme0@juno.com> wrote in message news:3F821B4D.2000304@juno.com...
: Dave Platt wrote:
: > In article <3F8153DA.1090301@juno.com>, mike <spamme0@juno.com> wrote:
:
:
: >>ExcUUUUUUUUse me???
: >>What about hooking two ohm-meter leads to two points on a cable
: >>and reporting the result "will not work"? I'm sticking my neck out and
: >>will guarantee
: >>that if you stick one lead on the probe tip and the other on the
: >>center of the bnc, you WILL get a reading somewhere between
: >>zero and infinity ohms. What's the number?
:
:
: > If the coax isn't shorted somewhere inside, then a standard DC
: > ohmmeter reading of the center-conductor-to-braid resistance will be
: > as close to infinity as matters.
:
: Except that I said from probe tip to bnc center conductor. Nowhere did
: I mention braid, shield, ground or any other terminal.
:
: If the ohmmeter doesn't read nearly
: > infinite, it's due to leakage somewhere (even fingertip contact with
: > the probes or coax conductors could pull the reading down to a few
: > megohms).
:
: > Whatever reading comes out of the ohmmeter, will have _no_
: > relationship at all to the cable's characteristic (or surge)
: > impedance. 50-ohm cable such as RG-58, 75-ohm such as RG-59, 93-ohm,
: > 150-ohm cable... they'll *all* read nearly infinite DC resistance from
: > center conductor to braid/shield.
:
: There you go with that braid again.
:
:
: > The characteristic impedance
:
: I never mentioned characteristic impedance either...
:
: can be measured only using radio
: > frequency techniques, TDR or similar impulse measurements, etc. You
: > simply cannot determine it using a DC ohmmeter.
:
: Pet Peeve Alert:
: I love it when people chime in with authoritative statements about
: issues well beyond their area of expertise. Seems the farther it gets
: from the issues, the more people weigh in.
:
: Let's review...
: About all we actually KNOW is that the OP has some unknown 1X probe and
: a question about a number.
:
: In such instances, it's often tutorial to ask a well-formed question that
: will provide additional data and maybe even lead the OP to a direct
: answer to his question.
:
: Then we get people (who apparently didn't read the question) jumping in
: to say that the question is wrong and
: proceeding to detail why some other question would have been wrong.
:
: I don't have the Psychic Hotline on speed dial. I don't know anything
: about the OP's probe. But I can give some general information.
:
: Tutorial starts here:
: It's difficult to get a signal into a 1 Meg scope input. Most probe
: leads act like relatively low impedance transmission lines. It's not
: possible to terminate them. 'bout all you can do is stick some
: resistance in series to damp reflections. Turns out that it works a lot
: better if you distribute the resistance along the transmission line.
: Quality probes are made with special coaxial transmission line with
: resistance wire for the center conductor.
:
: So, if you were to make a resistance measurement from probe tip to the
: center pin of the BNC, you just might measure some resistance. And if
: that resistance were approximately the number in question, you might
: have an answer to your question.
:
: Flame suit on...take another shot from the hip.
:
: mike
:
: --
: Bunch of stuff For Sale and Wanted at the link below.
: laptops and parts Test Equipment
: 4in/400Wout ham linear amp.
: Honda CB-125S
: 400cc Dirt Bike 2003 miles $550
: Police Scanner, Color LCD overhead projector
: Tek 2465 $800, ham radio, 30pS pulser
: Tektronix Concept Books, spot welding head...
: http://www.geocities.com/SiliconValley/Monitor/4710/
:
Click to expand...


--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
4in/400Wout ham linear amp.
Honda CB-125S
400cc Dirt Bike 2003 miles $550
Police Scanner, Color LCD overhead projector
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
And since I went to all the trouble of going up in the attic to fetch
some probe cable, I measured it. This particular stuff is 38 ohms/foot.
That's DC RESISTANCE OF THE CENTER CONDUCTOR.
NOTE THAT THIS IS NOT, NOT, NOT THE Zo...IT IS DC RESISTANCE!!!!!!!
MEASURED WITH AN OHM-METER, NOT A TDR!!!! OF THE CENTER CONDUCTOR,
NOT THE SHIELD, BRAID, OR ANY OTHER TERMINAL.
I DON'T KNOW HOW TO BE MORE CLEAR, SO I'LL JUST SAY IT LOUDER!!!!!
;-)
Click to expand...
Makes perfect sense to me.
Measurement cables don't need to be lossless, but they do need to be nicely
damped, so they are rather resistive.

Measure a tek scope probe lead.
 
Walter Harley wrote:

"William P.N. Smith smith@compusmiths.com>" <w<underscore> wrote in message
news:96r5ovgn8gk47ope8mkhvj2d7q8a1ic9qg@4ax.com...
"Eric" <some1@clare.co.nz> wrote:
what we are trying to tell you Mike [...]

Hey, if we can quit wrangling over how to measure the impedance of a probe,
maybe we can get back to the OP's actual question - I'd love to know the
answer myself. That question was:

"What uses 215 ohm impedance?"

If s/he'd asked "what uses 75 ohm impedance" or "what uses 50 ohm impedance"
or "what uses 600 ohm impedance" I'd have some answers (no doubt answers
s/he already knows)... But I've never heard of a transmission system built
around 215 ohms.

Has anyone else?
Click to expand...
That's what I was looking for, not to start a war over impedance... (cringe)
Maybe if someone just said 'Oh that's a standard for probing klystron repeller
plates' I'd be happy.
But the probe just sits there, defying me all day at work. And yes, it measures
about 200 ohms from the tip of the probe to the pin in the BNC. And there
doesn't seem to be an attenuator in there either, just looks like a BNC plug...
 
Dave VanHorn wrote:
And since I went to all the trouble of going up in the attic to fetch
some probe cable, I measured it. This particular stuff is 38 ohms/foot.
That's DC RESISTANCE OF THE CENTER CONDUCTOR.
NOTE THAT THIS IS NOT, NOT, NOT THE Zo...IT IS DC RESISTANCE!!!!!!!
MEASURED WITH AN OHM-METER, NOT A TDR!!!! OF THE CENTER CONDUCTOR,
NOT THE SHIELD, BRAID, OR ANY OTHER TERMINAL.
I DON'T KNOW HOW TO BE MORE CLEAR, SO I'LL JUST SAY IT LOUDER!!!!!
;-)


Makes perfect sense to me.
Measurement cables don't need to be lossless, but they do need to be nicely
damped, so they are rather resistive.

Measure a tek scope probe lead.



gents, look at this url, www.precisionspeed.com/sender.htm ,they got
Click to expand...
some instrument using 215 ohms impedence. don't knows what it is good for
rw
 
what we are trying to tell you Mike

it might have an impedance of 215 Ohms

But you can NOT measure it with DC current, no were will you find it with DC
current, full stop.
Click to expand...
Having read the thread to here, it is obvious to me that you did NOT read
what Mike posted before you responded to it. Maybe you skimmed it, but
you did NOT read it.

Mike referred to the possibility of actual, DC measureable, resistance having
been deliberately introduced in series along the center conductor -- which
would, indeed, be measureable with a DC current, also along the center conductor,
if such resistance(s) were present. He also provided sound reasoning based on
RF propagation issues why such actual resistance might have been so introduced.

Your objection applies to something orthogonal (in the geometric and linear
algebra senses) to what Mike wrote. While it is a valid objection to what
you clearly inferred Mike had written, (the inability of DC instrumentation
to measure surge or characteristic impedances), it has nothing to do with what he
actually wrote.

HTH
Kevin
 
A E wrote:

What uses 215 ohm impedance?
Going through my new desk at work I came across an otherwise unmarked scope
probe that reads "215 ohms 1:1".
No one else seems to know what it's for either. It's manufactured, not home
made.
Any thoughts?
Thanks,
Alex
Click to expand...
Alright guys, let's all calm down here.... I think that this probe is nothing
more than a standard 1:1 scope probe...
I'm so occupied with exotic stuff that a simple scope probe threw me... I've
never seen a 1:1 probe before in my life, always those 10:1s with a switch for
the 1:1 mode, and they *never* had the series resistance printed on the body ...

I just started this new job so I thought that those 215 ohms could be some
uber-exotic thing, guess not!
It's just a probe with a cable that ends in a BNC connector, that's it, that's
all...
 
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