I have question about R L Mathematics

All I see is the URLs, but with the enough information to download with wget.

Please tell me those wire gimmicks that hold the probes aren't enameled magnet wire. They look awful dark, here.

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"Design is the reverse of analysis" 
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Reply to
Fred Abse
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Nope they're stripped clean with a great tool. I'll post it under the same thread in abse. Got when I worked at a motor rewind shop 32 years ago. Mikek

Reply to
amdx

Is that alt.binaries.schematics.electronic or alt.binaries.schematics.electronics I never could figure out which is the correct newsgoup.

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Jeff Liebermann     jeffl@cruzio.com 
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Reply to
Jeff Liebermann

I posted to alt.binaries.schematics.electronic but I was not feeling up to figuring out how to post my pics properly. I've done it before but these didn't post as I wanted. Do you have a problem viewing photobucket pictures? Did you get the 3B7 scans? Life in my city should return to normal tomorrow, temps going up to 61*. Mikek

Reply to
amdx

Thanks. I'll look into it.

Reply to
John S

Hi, Mike -

I have reviewed your pictures and re-read the posts and I have a couple of new comments.

  • I don't know how you verified that your probes are a problem, but I suggest applying the same signal to both, recording the results, swapping channels, and see if the problem follows the probes or not. If the problem follows, it's the probes. If not, it's the scope channels.

  • The ll feet of coax alone will cause almost 11ns of delay. Since you have it coiled on each end, the delay will be more than that. This leaves us in an even worse situation to explain high R and low L.

  • If you, by any chance, have another 11-feet piece of coax without the cores, try measuring that.

Good luck.

John S

Reply to
John S

Yes that's what I did, problem follows the probes. I'm not surprised, I have done a major repair to the metal housing that was broke in two pieces. I seem to have ruined a solder tip soldering the metal the housing is made off. The probes are at least 30 years old. I didn't receive my new probes yesterday (as told) maybe today.

I'll have to check that, an see if my "setup" verifies that.

This

Ya, hmm. I did find a data sheet for 3B7 but the loss graph only goes to 500kHz. I'll take the book with me to work and see how the losses of this material compare to others. Don't know if it is high loss or low loss.

I will be busy all weekend, working for a living, I hope I can try something sooner, but it might be next Tuesday.

Reply to
amdx

Okay. Use one probe to measure both amplitudes. Use both probes to measure the phase (at zero-crossing only) while ignoring the amplitudes.

Otherwise, use your new (calibrated by you and verified by you) probes.

I would not expect 3B7 to be of significant inductance at your frequency of interest. It might be instructional to insert the coax into a piece of conduit of the same length and measure it.

I understand. I don't mean to push you.

John S

Reply to
John S

Please, I don't feel pushed, this stuff is fun, I want to get back to it. Can't wait to retire, so I can play all day. I seem to recall a video of an aging Navy lady, she was teaching. She ask what is a nanosecond, then held up 1 foot of wire and said, this is a nanosecond. So, ya, 11 ft, 11ns, thanks for the memory jog. I found the video, Admiral Grace Hopper, fun to watch.

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It amazes me that I can see the the delay in a short piece of wire. All of the sudden I see a value in my new 300 Mhz scope. Lower time base.

Let me setup the proposed experiment. I'm measuring the delay in the shield of a coax. The R will be near zero ohms so I'll probably change my sense resistor to a low value, maybe one ohm, if I can find one. I should probably use a series 50 ohm resistor to protect the 50 ohm in the signal generator. Halt. I'm rethinking that, I already have a 47.5 ohm sense resistor, so I think I'm all set. Won't there me some additional delay caused by the inductance of the wire? What is the inductance of a ft of wire. Found this calculator.

I picked 0.5 cm for the dia. of coax shield. (?) I'm at work can't measure, I don't know how a braided shield compares to a solid wire. The calculator gives me 3.2uH for 11 ft of wire. Please check that for me, seems high, but it is a weak, seems :-) Anyway, my first guess is I have a delay caused be length and a delay caused by inductance. We will see.

Mike

Reply to
amdx

alt.binaries.schematics.electronic

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)
Reply to
Fred Abse

They don't look stripped around the probes.

I use tinned copper wire for such things.

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)
Reply to
Fred Abse

OFF TOPIC, SLIGHTLY:

With a wideband scope, you see many interesting things, including some that might surprise you. Years ago, while looking at some short pulses (to evaluate the response of a new amplifier), I saw unexpected "steps" in the traces. I was using BNC T-connectors and my test setup had accidentally duplicated a TDR function. The impedance change reflections were plainly evident in a few feet of 50-ohm coax. (I've since seen plans for a home-brew TDR similar to my accident. :-)

I enjoy amazement, too.

"Sal" (KD6VKW)

Reply to
Sal M. O'Nella

I saw a complete program on PBS about her. It was fascinating.

I use 1nH/mm as a rule-of-thumb for a straight wire. For an 11-foot straight wire, that would give about 3.3uH. But, remember that your wire has additional inductance in the coiled portions.

Reply to
John S

Right you are, Sal. I once used a 200MHz scope and a pulse generator to measure the approximate length of a reel of coax. Handy stuff to know.

John S KD5YI

Reply to
John S

About 20 years ago there was a TV show on the PBS called the Computer Chronicals. She was often on that program. She was given credit for the terms bugs in the computer and debugging. Came from a moth in one of the old relay type computers around the WW2 time.

She also has a navy ship named after, one of only 2 US navy ships named after a woman.

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Reply to
Ralph Mowery

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"Sal" (USN 1962 - 1982)

Reply to
Sal M. O'Nella

Ok, I checked the pictures, must be the lighting on my bench. The wires are stripped clean, the wire had red varnish, I stripped it clean. I'm a highly experienced wire stripper. :-) Mikek

Reply to
amdx

I could learn a lot from you.

Reply to
John S

As I posted earlier, I have a very handy tool I got 30 years ago while working at an electric motor rewind shop.

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I've looked several times over the years, I can't find anything similar. Mine has a crack in one blade, I might buy a backup if I new where to buy it.

I'm not sure if you were being sarcastic or not, but I get to react however I want :-)

Mikek

Reply to
amdx

I was very serious. Sarcasm is not my intent. I have nothing to gain from it.

Reply to
John S

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