Powering 8-ohm speaker through ~130 feet of RG6 coaxial? - AVS Forum
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post #1 of 44 Old 08-19-2013, 10:25 AM - Thread Starter
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I'm not at all pleased with using this method, but it's an option I need to consider. Customer wants to power an additional speaker that wasn't part of the original plan, and this approach might be the least worst option, given a number of trade-offs that I can't go into for NDA reasons.

The back of the audio/video receiver connects to many RG6 coaxial cable terminals, all of which run down two floors to the basement. There, I'll mate that RG6 run with another that runs up two floors, to power a single speaker. At both ends, speaker wire will be mated to RCA, and then an RCA-to-coaxial adapter gets the signal into the RG6 coaxial cable. Is there an amplifier that would work well for this, for installation in the basement switchboard, so that the receiver doesn't see as much resistance as it would otherwise see? As I've never done anything similar to this before, I don't know what to expect. One idea I had was to use one coax cable for positive, and one separate coaxial cable for negative. I believe that coaxial cables have a thin gauge center conductor, so it would seem wise to bypass it somehow.

Advice would be sincerely appreciated.

-John
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post #2 of 44 Old 08-19-2013, 09:28 PM
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I'd suggest you connect all that cable up and short one end of it. Now go to the other end with an ohmmeter. If it's more than an ohm or two it's really going to suck at being speaker wire.
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post #3 of 44 Old 08-20-2013, 12:54 AM
 
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Quote:
Originally Posted by olyteddy View Post

I'd suggest you connect all that cable up and short one end of it. Now go to the other end with an ohmmeter. If it's more than an ohm or two it's really going to suck at being speaker wire.
To find the true resistance of the wire, you have to take 1000 divide by the feet (length of the wire), then multiply by the measured resistance of the wire.

Since the Stinger in most RG-6 is going to be around 18awg, you should come up with an answer around 0.83 Ohms. Standard 12awg wire will be 1.565, 16awg 3.959. Here is a table that shows ohms for wire gauge per 1000 feet http://www.tfcbooks.com/referenc/wiresize.htm You can also use this online calculator to figure it out for you http://www.cirris.com/testing/resistance/wire.html

Now to throw in that the outer shield will be around 14-16awg, you have to calculate that also into the total resistance, which would still come in around what stranded 12-16awg speaker wire per one conductor, not both added together, so the OP should be fine. It is really no different then if they were using 12/2 or 14/2 NM Romex or THHN/THWN for the speaker wire from one end to the other, as is done in commercial applications, vs. pulling CL-2 or CL-3 rated wires.
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post #4 of 44 Old 08-20-2013, 04:10 AM
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To find the true resistance of the wire, you have to take 1000 divide by the feet (length of the wire), then multiply by the measured resistance of the wire.

No, you don't. You do as Olyteddy suggested and measure it with an Ohmeter.
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post #5 of 44 Old 08-20-2013, 07:12 AM
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You cannot talk about theoretical trade offs because of an NDA??? Well at least they allowed you to talk about resistance.

Are we talking high quality audio performance?

How about running line level audio to a powered speaker?
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Regards, Frederick C. Wilt
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post #6 of 44 Old 08-20-2013, 07:43 AM
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Originally Posted by SAM64 View Post

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To find the true resistance of the wire, you have to take 1000 divide by the feet (length of the wire), then multiply by the measured resistance of the wire.

No, you don't. You do as Olyteddy suggested and measure it with an Ohmeter.
Yeah, that.
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post #7 of 44 Old 08-20-2013, 11:11 AM
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Quote:
Originally Posted by gregzoll View Post

To find the true resistance of the wire, you have to take 1000 divide by the feet (length of the wire), then multiply by the measured resistance of the wire.

Since the Stinger in most RG-6 is going to be around 18awg, you should come up with an answer around 0.83 Ohms. Standard 12awg wire will be 1.565, 16awg 3.959. Here is a table that shows ohms for wire gauge per 1000 feet http://www.tfcbooks.com/referenc/wiresize.htm You can also use this online calculator to figure it out for you http://www.cirris.com/testing/resistance/wire.html

Now to throw in that the outer shield will be around 14-16awg, you have to calculate that also into the total resistance, which would still come in around what stranded 12-16awg speaker wire per one conductor, not both added together, so the OP should be fine. It is really no different then if they were using 12/2 or 14/2 NM Romex or THHN/THWN for the speaker wire from one end to the other, as is done in commercial applications, vs. pulling CL-2 or CL-3 rated wires.

The shield would only be equivalent to 14-16ga if it was copper braid. Most CATV RG6 is foil shield with four or less 26ga drain wires. And with an 18ga center conductor, that as good as it gets. For background music, it should work fine. But for critical listening this solution will come up short.

The 1000 foot number comes from the fact that most bulk cable is sold in 1000 foot lengths. The data sheets specify the resistance at 1000 feet as it's a more manageable number. That is where you need to divide by 1000. If measuring a cut cable, the resistance is what ever it reads.

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post #8 of 44 Old 08-20-2013, 11:18 AM
 
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Originally Posted by Glimmie View Post

The shield would only be equivalent to 14-16ga if it was copper braid. Most CATV RG6 is foil shield with four or less 26ga drain wires. And with an 18ga center conductor, that as good as it gets. For background music, it should work fine. But for critical listening this solution will come up short.

The 1000 foot number comes from the fact that most bulk cable is sold in 1000 foot lengths. The data sheets specify the resistance at 1000 feet as it's a more manageable number. That is where you need to divide by 1000. If measuring a cut cable, the resistance is what ever it reads.
Read the whole info, or use the calculator. There is a specific resistance that will be with any gauge wire, and if you want to cheat, you use the online calculators. If you want exact numbers, without the online calculator, you use the formula as stated, which has been used for hundreds of years to figure exact resistance for the length of wire.

Now where the fun comes in, is if you do not know the exact length of wire, then you have to use Algebra to have the Length being X, and taking the info you already know, to calculate what X is. BTW, RG-6 is used all the time for Component runs, for audio also, besides Video, due to it is easier to pull a bundle of RG-6 from point A to Point B if it is a short run, or even if say it is a run of what the OP has, if you are centralizing the equipment, and that is all you have to work with, which is what it sounds like the OP is dealing with, and the clients are paying the bills, so they have to go by what they dictate.
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post #9 of 44 Old 08-20-2013, 11:29 AM
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Originally Posted by gregzoll View Post

Read the whole info, or use the calculator. There is a specific resistance that will be with any gauge wire, and if you want to cheat, you use the online calculators. If you want exact numbers, without the online calculator, you use the formula as stated, which has been used for hundreds of years to figure exact resistance for the length of wire.

Now where the fun comes in, is if you do not know the exact length of wire, then you have to use Algebra to have the Length being X, and taking the info you already know, to calculate what X is. BTW, RG-6 is used all the time for Component runs, for audio also, besides Video, due to it is easier to pull a bundle of RG-6 from point A to Point B if it is a short run, or even if say it is a run of what the OP has, if you are centralizing the equipment, and that is all you have to work with, which is what it sounds like the OP is dealing with, and the clients are paying the bills, so they have to go by what they dictate.

Determining the length based on resistance only works if you know the exact resistance of a 1000 foot run. Is the RG6 center conductor copper or copper clad steel? What is the shield comprised of? You can't take some basic electrical wire chart and apply it to a coax cable of unknown origin.

And again if I want to know the round trip resistance of an electrical wire run already in place, I simply measure it with one end shorted. It doesn't matter if the center conductor or shield is of a higher gauge. In a speaker circuit, the total round trip resistance is all that matters.

You take these online publications, misinterpret them, and then confuse the posters when there are much simpler solutions that have already been suggested.

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post #10 of 44 Old 08-20-2013, 11:49 AM
 
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Originally Posted by Glimmie View Post

Determining the length based on resistance only works if you know the exact resistance of a 1000 foot run. Is the RG6 center conductor copper or copper clad steel? What is the shield comprised of? You can't take some basic electrical wire chart and apply it to a coax cable of unknown origin.

And again if I want to know the round trip resistance of an electrical wire run already in place, I simply measure it with one end shorted. It doesn't matter if the center conductor or shield is of a higher gauge. In a speaker circuit, the total round trip resistance is all that matters.

You take these online publications, misinterpret them, and then confuse the posters when there are much simpler solutions that have already been suggested.
No, you confuse the other party, when you tell them to go by what the meter tells you, not by what the charts, which have been used for decades, along with the formula that has also been used by EE's and Master Electricians for decades, to come up with the real resistance of a run.

It is a method that has worked for those that do this stuff all the time, and know how to use the info, which it is obvious that you do not, because you are telling them to go by the resistance of a shorted conductor, which is not the correct way to determine true real resistance of a wire.

I am not going to sit here and argue with you back and forth on this, because you do not listen, nor read the information posted, by myself or others, when it is factual backed up info, not something just pulled out of the air like you and a few others do on here.
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post #11 of 44 Old 08-20-2013, 12:00 PM
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Originally Posted by gregzoll View Post

No, you confuse the other party, when you tell them to go by what the meter tells you, not by what the charts, which have been used for decades, along with the formula that has also been used by EE's and Master Electricians for decades, to come up with the real resistance of a run.

It is a method that has worked for those that do this stuff all the time, and know how to use the info, which it is obvious that you do not, because you are telling them to go by the resistance of a shorted conductor, which is not the correct way to determine true real resistance of a wire.

I am not going to sit here and argue with you back and forth on this, because you do not listen, nor read the information posted, by myself or others, when it is factual backed up info, not something just pulled out of the air like you and a few others do on here.

The information links you posted are quite accurate. The problem is they do not fit the problem the OP has. The practice you propose is for predicting the resistance of a run while on paper or in the engineering stage. Or it can be used to find a short as well. But this information is useless unless you have the specs on the coax cable you are trying to estimate the resistance of. You can't assume all RG6 coax cable is 18ga copper and braided shield because there are many options here. How about quad shield versus dual shield? You don't think that changes the total run resistance? How dense a braid if any? What gauge are the drain wires with a foil shield? How many drain wires?

Really, measuring a shorted coax cable will not give me the true round trip DC resistance of the cable? You are clueless!

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post #12 of 44 Old 08-20-2013, 12:20 PM
 
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No Glimmie, you are clueless. Maybe you should stop while you are behind and also start researching facts, not just assuming stuff. Regardless what the OP may not know about the wire spec's, all they need to know is what the resistance is, the length of the cable, and then go by the info I posted, which will give them the real true resistance of the length of wire. Again, it has worked for decades, and will continue to work, because it is the way that you calculate the real resistance of a loop of wire, regardless what you think.

It is also basic Electric 101, but then again, no one can tell you different, because you have it set in your head that you are the only authority, along with a couple of others on here, that want everyone that comes along to only believe what your little group wants them to know.
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post #13 of 44 Old 08-20-2013, 12:24 PM
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Originally Posted by gregzoll View Post

No Glimmie, you are clueless. Maybe you should stop while you are behind and also start researching facts, not just assuming stuff. Regardless what the OP may not know about the wire spec's, all they need to know is what the resistance is, the length of the cable, and then go by the info I posted, which will give them the real true resistance of the length of wire. Again, it has worked for decades, and will continue to work, because it is the way that you calculate the real resistance of a loop of wire, regardless what you think.

It is also basic Electric 101, but then again, no one can tell you different, because you have it set in your head that you are the only authority, along with a couple of others on here, that want everyone that comes along to only believe what your little group wants them to know.

Why can't you respond to the technical issues I raised?

Well lets just appeal this to the membership at large here.

See who they think is correct.

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post #14 of 44 Old 08-20-2013, 12:48 PM
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Assuming the cable does not have a short between the center conductor and the shield, at some point between the ends, then shorting the center conductor to the "shield" at one end and measuring the resistance at the other end between the center conductor and the "shield", with an ACCURATE meter, will give you the actual AVERAGE RESISTANCE of that length of "wire" from end to end and back.

It won't tell you how much of that resistance comes from the center conductor and how much from the "shield" but that doesn't matter in this scenario.

You will want to insure that all of the drain wires, all of the braid, etc that make up the "shield", are connected together and contributing to the overall resistance.

If you knew the actual part number of the cable AND the length you could go to the manufactures specs and compute the number BUT it will NOT yield a more meaningful answer.


I still would be inclined to run line level through the coax and use a powered speaker (or a small "modular" amp and speaker).

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post #15 of 44 Old 08-20-2013, 01:42 PM
 
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Originally Posted by Glimmie View Post

Why can't you respond to the technical issues I raised?

Well lets just appeal this to the membership at large here.

See who they think is correct.
I already did, but it is obvious that as usual you are not listening.
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post #16 of 44 Old 08-20-2013, 01:43 PM
 
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fcwilt, if there was a short in the middle or anywhere in the run, it would come up infinite, not an actual resistance reading. Open you would not get any reading at all.
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post #17 of 44 Old 08-20-2013, 01:48 PM
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Originally Posted by gregzoll View Post

No, you confuse the other party, when you tell them to go by what the meter tells you, not by what the charts, which have been used for decades, along with the formula that has also been used by EE's and Master Electricians for decades, to come up with the real resistance of a run.

Pretty sure an Ohmmeter will measure the total resistance of the wire in place. If it doesn't, change the batteries. wink.gif

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post #18 of 44 Old 08-20-2013, 01:52 PM
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Originally Posted by gregzoll View Post

I already did, but it is obvious that as usual you are not listening.

Those charts you posted are for "SOLID COPPER WIRE".

Now how does that relate to copper clad steel wire sometimes used in RG6 and how does that account for the various types of shield conductors and configurations?

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post #19 of 44 Old 08-20-2013, 02:05 PM
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Originally Posted by jautor View Post

Pretty sure an Ohmmeter will measure the total resistance of the wire in place. If it doesn't, change the batteries. wink.gif

Good point on the fresh batteries. Low ohms is where accuracy first starts to suffer with weak batteries.

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post #20 of 44 Old 08-20-2013, 02:08 PM
 
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Originally Posted by jautor View Post

Pretty sure an Ohmmeter will measure the total resistance of the wire in place. If it doesn't, change the batteries. wink.gif
If there is a dead short on a wire, it will measure infinity on the resistance reading. If you change the batteries and it still reads Infinite, you have a dead short, and wasted time and effort changing batteries for no reason.
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Originally Posted by Glimmie View Post

Those charts you posted are for "SOLID COPPER WIRE".

Now how does that relate to copper clad steel wire sometimes used in RG6 and how does that account for the various types of shield conductors and configurations?
It still applies regardless what you believe. If you took the time to read the before mentioned link, the rules still apply in calculating real ohms of a wire run, regardless what the material is.
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post #22 of 44 Old 08-20-2013, 02:10 PM
 
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Good point on the fresh batteries. Low ohms is where accuracy first starts to suffer with weak batteries.
Incorrect. Weak batteries will cause the meter to not read at all, or will still give a reading. It will not give low Ohms reading. You want a low Ohm reading, not high when measuring a circuit.
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post #23 of 44 Old 08-20-2013, 02:16 PM
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Originally Posted by gregzoll View Post

Incorrect. Weak batteries will cause the meter to not read at all, or will still give a reading. It will not give low Ohms reading. You want a low Ohm reading, not high when measuring a circuit.

Perhaps I wasn't clear.

When the batteries are weak, the accuracy of low ohms readings is compromised. I have seen this on quite a few DMMs. The reason is probably because in low ohms measurment, more current is needs to push through the loop, which weak batteries lack.
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If there is a dead short on a wire, it will measure infinity on the resistance reading. If you change the batteries and it still reads Infinite, you have a dead short, and wasted time and effort changing batteries for no reason.

BTW, what is a "dead short"? Does that mean zero ohms resistance?

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post #24 of 44 Old 08-20-2013, 03:05 PM
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Originally Posted by fcwilt View Post

No a short from center to shield would make the round trip from the end being measured shorter, thus the resistance would be less.

To read infinite you would need to have a break in the center or shield - thus yielding an open circuit.

You're WRONG! Read post #32 & 33. biggrin.gif

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post #25 of 44 Old 08-20-2013, 03:20 PM
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You're WRONG! Read post #32 & 33. biggrin.gif

No I am correct.

An open circuit will measure INFINITE resistance.

Ohm's law: I = V / R

With an open circuit no current can flow thus I is zero. Re-arrange the formula to R = V / I. Now we know that when the denominator is zero the answer is undefined. But as I approaches zero R approaches infinity.

Touch the probes of the meter together (a short circuit) and you will read zero ohms. Use a short piece of wire (in the gauges we are talking about) and it will likely still read zero because the resistance of the wire is so low the meter cannot give an accurate reading - at least a typical handheld low cost meter. As the length of the wire is increased the resistance will rise and eventually you will get a reading. The length at which you get a meaningful reading will depend upon the quality of the meter and the resistance-per-foot of the wire.

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post #26 of 44 Old 08-20-2013, 03:23 PM
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No I am correct.

An open circuit will measure INFINITE resistance.

Ohm's law: I = V / R

With an open circuit no current can flow thus I is zero. Re-arrange the formula to R = V / I. Now we know that when the denominator is zero the answer is undefined. But as I approaches zero R approaches infinity.

Touch the probes of the meter together (a short circuit) and you will read zero ohms. Use a short piece of wire (in the gauges we are talking about) and it will likely still read zero because the resistance of the wire is so low the meter cannot give an accurate reading - at least a typical handheld low cost meter. As the length of the wire is increased the resistance will rise and eventually you will get a reading. The length at which you get a meaningful reading will depend upon the quality of the meter and the resistance-per-foot of the wire.

I was joking, obviously!

I just can't believe how absurd those posts by Gregzoll I referenced are. He obviously has no clue what the reading on the meter means - digital or analog meter. It's down right scary when you think he gives others here advice on primary household electrical wiring and grounding. And it's also obviously not a typo either. I gave him several chances to think it out.

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post #27 of 44 Old 08-20-2013, 03:32 PM
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Originally Posted by Glimmie View Post

I was joking, obviously!

I just can't believe how absurd those posts by Gregzoll I referenced are. He obviously has no clue what the reading on the meter means - digital or analog meter. It's down right scary when you think he gives others here advice on primary household electrical wiring and grounding. And it's also obviously not a typo either. I gave him several chances to think it out.

Sorry I missed the significance of the little icon.

It is interesting how confused people can be and yet they will insist they are correct. Human nature is a funny (and scary) thing sometimes.

Perhaps he is just jerking people's chain?

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post #28 of 44 Old 08-20-2013, 03:35 PM
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And while I am a fan of MP I don't remember what is taking place in the referenced photo.

What is the name of that sketch?

I would like to go watch it again.

Regards, Frederick C. Wilt
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post #29 of 44 Old 08-20-2013, 03:52 PM
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Quote:
Originally Posted by Glimmie View Post

I was joking, obviously!

I just can't believe how absurd those posts by Gregzoll I referenced are. He obviously has no clue what the reading on the meter means - digital or analog meter. It's down right scary when you think he gives others here advice on primary household electrical wiring and grounding. And it's also obviously not a typo either. I gave him several chances to think it out.

Not only is he clueless, but insults anyone who tries to correct him...yet he's still allowed to post.
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post #30 of 44 Old 08-20-2013, 04:00 PM
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INFINITE OHMS. Note the open meter leads. The needle is at 1Kohms which is actually the infinity symbol but it's too small to see here.


ZERO OHMS: Note the shorted test leads. The needle is on 0.

Next episode: a DMM.

So Greg, what do you say? Hmm, it looks like I do know how to use a multimeter after all doesn't it?
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