I have question about R L Mathematics

Hi Mike, I'm confused (which is normal). Both the shield and center condu ctor are going through the same bead? In theory with 'perfect' coax this s hould do nothing (All the E/M fields are contained within the coax.) But m aybe you have a different setup. And of course coax is not perfect. To measure L, I'd pick a know capacitance and then find where it resonates. (I guess a bit harder with coax with already some C in there... but maybe pick a C much bigger than the capacitance of the coax.)

George H.

I have a feeling you didn't look at any of my pretty pictures, I think at least one layer of fog should have dissipated if you did. They're really pretty.

I'm doing that now, only with 42 halves. I can try it with one, but I question with my "setup" will resolve that inductance.

I already did that, zero inductance or resistance.

Do you need any potcores?

Since you have used "ohms-guesser" I guess I need to ask, What is that? and does it use ac or dc for the measurement?

The number is (obviously) wrong because nowhere in your

I'm sure you understand that ferrite beads on a transistor lead, show up as a resistive and inductive. Why is this different? Here's a pdf with a graph page 4 right side showing R, X, and Z. Hand picked to show what I want it to! Although I should have secretly altered the frequency range.

It's inductive.

LOL, you're right, it was my hand.

Good luck. I'm in Fl. where people are acting like the end is near. We are slightly below freezing and businesses are closing, schools out. The weather men are have fits of frenzy. If I was back in Michigan, we would be happy it got warmer, because we were getting tired of starting the car at 7* in 8 inches of snow. Mikek

Most of my info was measuring the impedance of the shield through the ferrite, no other connections. It was R=3k XL=1.2k approx. I did do a test with one end shorted, looking into the other end, and you are correct, it measured zero inductance and zero ohms.

Yea, my "setup" is different. :-) I describe it with pictures after Wimpie ask. Time was 3:17 on the 28th.

And of course coax is not perfect.

I can revisit. I did bring it near 0* phase with 3700pf, but it was not sharp and I should have added more capacitance to pass through resonance for a better understanding. "Not sharp" probably because of the 3k Resistance.

I'm not sure I understand what you're trying to measure. I assume that it's the effect of the "beads" on the inductance of the outer conductor, in which case, 3350 ohms looks way OTT. No pot core material I know of is

*that* lossy.

How long is the coax sample? 17ns is the delay of approx. 5 meters of wire at 3.85MHz, without any inductive loading.

You did connect to the outer conductor at both ends, didn't you. Preferably short inner to outer, at both ends.

There's no such thing. Reactance is merely the imaginary part of a (complex) impedance.

Lets look at what you have:

You have voltage/current=3350 ohms. That is the *magnitude* of the impedance, at an angle of 23.5 degrees, current lagging.

That's 3350 angle 23.5 ohms.

We now do a polar to rectangular conversion on that, giving:

3072 +j1335 ohms.

3072 seems way too high for the loss component, 1335 ohms is 55 microhenries,at 3.85MHz.

One thing I suggest is that you do the whole thing again, without, and then with, the "beads". That way, you can eliminate propagation delays.

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)

That is correct.

That's what everyone seems to think. I'm the odd man out. If you haven't looked at the picture, here it is. The ferrite is 18 inches long. That is a quarter in front.

It is 11 ft long.

Yes, outer conductor connected at both ends. To different inputs of the measuring device.

That I have not done. I'll try that. .......

......

OK, I'm back. Shorting the center pin to the shield, (at both ends) made absolutely no difference in the magnitude or phase of the measurement.

LOL, I had to go back and see if I said that.

Now I'll say what I meant. I want to know the magnitude in ohms of the reactance. John S already solved that for me, thanks. He knows how to solve for what I want, not what I ask for. :-)

Already restated.

Good, agreement with John S.

Everyone agrees the loss component is to high. Oh, except me. :-) I think I have stated, I thought the L would be higher than the R. That's not what I'm measuring. I have no experience in ferrite losses, and no education regarding losses in ferrite. But I think my measurement are in the ballpark.

I'll try another piece of RG-58/U, I can't get the ferrite of the cable without cutting off a PL259.

This evening I'll wind a 55uH coil and find a 3,072 resistor. I'll put these in series and see how it measures compared to my lossy ferrites beads on a cable.

I already know this measures about 6% high, probably because of the sense resistor. Thanks, Mikek

Well, I found the 6% is actually the difference between my scope probes. That's only my first problem. I measured a 55uH inductor and 3090 ohm resistor in series, 3.85MHz and got 2778 ohms 19.9* phase difference. The calculated numbers are Z = 3,364 and I don't know how to calculate the phase angle. Later I'll check this at 100kHz and so if strays are causing errors. Mikek PS, I should have some new probes tomorrow.

I clicked, I looked, I saw, I failed to understand, I blundered onward. What did I miss?

You really want a vector impedance meter: Yeah, I know it's an antique. There are probably much better models available today, but not at the price. I had one at a previous employer and used it for measuring almost everything. 0.5 to 110 Mhz. I've been looking for a broken one (because I blew up the one I was using often enough to be familiar with the repair procedures) but can't seem to find one in my price range (i.e. free). Make sure it comes with the probe and power cord as both are difficult to find.

Never mind. You won't see it. At the time, I was trying to correlate the measured value with the theoretical Al. However, since the cores are not being used in the normal manner, that's not going to work or yield any useful results. Might as well measure the whole string at once.

No thanks. I gave smoking the stuff in college. You might be able to sell them in Colorado.

An ohms-guesser(tm) is a Harbor Freight DVM or equivalent. Usually sells for $5 or less. Capable of producing wrong values to at least 3

1/2 digit accuracy. I usually have several available for the inevitable visitors that roll into my parking lot wanting to borrow a meter to fix their vehicle electrical system. Ohms-guessers use DC current to measure resistance. There is also the volts-guesser and amps-guesser which offer similar features and lack of accuracy.

ARGH! I goofed. I forgot how ferrite really work and was assuming that it represented a pure inductance. Please ignore everything I wrote about the resistive component. I tried to find a reactance vs frequency graph for the 3B7 material and failed. Maybe later tonite. I'm buried in broken machines and an office in desperate need of untrashing. Thanks (grumble).

Incidentally, consider yourself off the hook for the MFJ-1800 yagi fiasco if you promise not to tell anyone how badly I messed up here.

Huh? Are they expecting Florida to sink into the ocean under the added weight of the snow?

In the People's Republic of Santa Cruz, it has been mostly 60-70F highs and 35-45F lows for most of the alleged winter. Quite pleasant and comfortable. The problem is that we've had less than an inch of rain this season, where normal would be about 15-20 inches by this date. The forest looks awful with dead trees and shrubbery everywhere. Looks like we're going to have a severe drought here. Even worse is the lack of snow for skiing. Right now, I could use some snow or rain.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Probably not much. :-( Very simple concept, Measuring current by use of a sense resistor. Then comparing voltage to current to get impedance.

I have recently acquired an HP 3570A Network analyzer and a 3330B synthesizer that are GPIB connected to a computer with custom software. It has not been powered for at least 10 years. The only problem I know about is the computer cmos battery most likely has failed. I've had it a couple months now and have not got it setup or attempted any use. I need to figure out what to do about the computer first. I don't have the original software disc, so I need to copy the program first thing.

You may have figured out, I'm not using this type of ohms guesser.

My deed here has been accomplished, I now officially close this thread. yippee, yahoo, hallelujah, praise be to any omnipotent powers.

Huh? Are they expecting Florida to sink into the ocean under the added weight of the snow?

In the People's Republic of Santa Cruz, it has been mostly 60-70F highs and 35-45F lows for most of the alleged winter. Quite pleasant and comfortable. The problem is that we've had less than an inch of rain this season, where normal would be about 15-20 inches by this date. The forest looks awful with dead trees and shrubbery everywhere. Looks like we're going to have a severe drought here. Even worse is the lack of snow for skiing. Right now, I could use some snow or rain.

-- Jeff Liebermann snipped-for-privacy@cruzio.com 150 Felker St #D

Santa Cruz CA 95060 Skype: JeffLiebermann AE6KS 831-336-2558

I have found through some tests and exchanges here that the mechanics of my "setup" work fine below 1MHz or a little higher. But I think, strays are causing some problems when I go higher in frequency. I should get my new probes today and I'll be working at tightening up the circuit and maybe adding shielding. I built this "setup" as as duplicate of the one I used, I tried to use it at higher frequency and I should not have.

When I was working with ultrasonics, our standard frequency was around

660 kHz. We used this daily to characterize piezo transducers to calculate matching to an amplifier. I sure wish the company made some money, I really enjoyed that job.

btw, Need any 2" disc piezo ceramic discs 1/16" thick PZT-8 material? I have a few other sizes also. Do you know any fun things I could do with them, besides give people shocks.

Thanks, Mikek

Jeff Liebermann scribbled thus:

All that rain is over here... Snow threatened :-(

--
Best Regards: 
                     Baron.

On 1/30/2014 9:33 AM, amdx wrote: (snip)

Hi, Mike -

I would like to buy a couple to experiment with and, possibly, learn something.

How many $ do you want and how do we connect?

Thanks, John S

Don't use those things, they're horrible. Designed around 1939, should have disappeared in 1940, attributed to a guy called Quackenbush. I think he was actually Groucho Marx ;-)

Soldering direct would be better, in this case.

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)

He's actually doing what a vector impedance meter does - the hard way.

A vector voltmeter might be of more use in Mike's case. More versatile.

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)

Where is one available and what would it cost?

Hi John, My address is good. These are 2" ceramics, 1/16", they resonate around 1.2MHz as I recall. We bonded them to 1/16" aluminum for approximately a 660kHz transducer. We drove them at antiresonance, where they measured around 20 ohms. We drove them continuous at 250 watts in an ice bath and 1000 watt pulsed. Send me an email. Mikek

There are a few HP8405 vector voltmeters on Ebay.

Be warned, the "probes" are actually miniature sampling heads, and can easily be ruined by overvoltage.

They did come with a set of accessories, but, judging by Ebay, these will likely have been split off, and sold separately.

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)

Attempting to do, and not the hard way the cheap way.

I built a tight unit this morning, 3.9% or 7.4% error measuring a 3090 ohm resistor, depending on which way I swap the scope probes*. The measurement didn't change from 100kHz to 10MHz, so now I think I've tamed the strays. When I get new probes and if they act identical, I'll work on accuracy.

I have one one the back burner. I want to try to work the kinks out of this, see if I can make an easy to build device for someone that has a scope and frequency counter, so they could check C, L or Z, at frequencies up to 10 MHz. Simple, at this point I have panel mount BNC, a 50* ohm resistor, small piece of perf board and wire.

Here's a couple of pictures to show the simplicity. The top picture shows the resistor under test. The bottom shows the sense resistor.

The sense resistor must be mathematically subtracted. A 50 ohm sense resistor with 15pf scope probe in parallel is changed by less than 0.1 ohm, at 10MHz.

• new probes on the way.

**I had a 47.5 ohm 1% resistor.

My browser doesn't support some of the more esoteric scripting that Photobucket uses.

Better to post to ABSE, I can actually read that.

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)

Took me three tries, but I got it all over there. Mikek

Re(Z)=3090 Im(Z) = 2 * pi * 3.85*10^6 * 55*10^-6

Phase angle = arctan (Im(Z)/Re(Z)

General rule: If Z = a +jb, Then phi = arctan (b/a), and mag(Z)=sqrt(a^2+b^2)

--
"Design is the reverse of analysis" 
                   (R.D. Middlebrook)