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General discussion

Anyone here work with smart coils?

Mar 6, 2008 8:30AM PST

They are used in place of ordinary load coils because they are dsl compatible. My question is do they really work? I still get the same voice problems at long distance as I did with all loads removed. This leads me to another question. How much attenuation on a line is too much and shouldn't load coils reduce it.
thank you;
Joe

Discussion is locked

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Load coils. . .
Mar 6, 2008 8:16PM PST
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Purpose of load coils as i understand it.
Mar 7, 2008 8:46AM PST

Load coils purpose is not to block all frequencies but voice. In the past that is just how they were made because that is all that mattered. The purpose of a load coil I think is to counter capacitance. The first one is placed at 3000' from office and then every 6000' thereafter. They essentially are coils of wire used to counter the capacitance of power influece from AC. Power influence is further countered by running Telephone on the opposite side of the road from power lines.
Anyway; In the midwest we are replacing the old loads and inserting the new ones that pass the required frequencies. I simply am wondering if they really matter? I have talked to others who remove all loads but the first one; which they replace with a smart coil. They say voice isn't affected up to 25,000'. I have tried both ways and I find that voice becomes lousy using both methods at extreme dsl range.

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Boy, now I'm going to have to remember now. . .
Mar 7, 2008 9:38AM PST

I taught this stuff back in the 80s and 90s.

The first load coil was constructed by Oliver Wheatstone in the late 1800s. He really didn't understand why it did what it does. The load coil is an inductor. Because of cable pair capacitance and self induction, voice transmission degrades as distance increases. The load coil effectively cancels the self inductance of the cable pair which in turn increases the voice band transmission distance. The load coil, being an inductor or more commonly a band pass filter, is designed for voice band frequencies. A load coil in that specific bandwidth has an effect of 3,000 feet on both sides of the coil. Thus, the first load coil is placed 3,000 feet from the office and the second is placed 9,000 feet from the office, which places the second coil 6,000 feet from the first. Subsequent coils are placed 6,000 feet apart. But the loading of a cable is not needed on phones less than 18,000 feet from the office. Beyond 18 KFt the cable pair is loaded. No phone shall be located beyond 3,000 feet from the last load coil. Another load coil must be installed. Load coils have no effect on power influence.

AC induction/power influence is a problem on long runs. Cable placement is important, but across the road does not always help. I remember my group chased a power induction problem in El Paso several years ago. An 1,800 pair exchange cable had "ground hum" on every pair. It was in conduit for a few miles, then broke off into buried and aerial. Engineering department fought this problem for several months, then contacted the power company. After another few months the power company found an unbalanced primary (27,00 KV) transformer on the other side of town. No one could ever explain it.

I've been out of the loop since 2000 so I don't know what a smart coil is. The last thing I taught is fiber optic multiplexers.

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Hmm.. I can accept that but......
Mar 7, 2008 10:03AM PST

What about line attenuation. That is what I think has now become the problem. For instance; today I installed dsl at a house 26,500' from the CO. My tester said that I was syncing up at 608k and was max capable of 1026K. This is all well and good but my attenuation was at 63db. The modems I use tend to drop off when attenuation gets above 60db. Of course voice quality will also suffer. Yes I loaded all the coils properly but coils aren't affecting the attenuation, either for the better or worse. What can I do to reduce or lower signal Attenuation?


PS. Isn't anyone curious how I can get dsl out that far? Yes, Dsl technology has progressed, but it still comes back down to the basics in the end. Please; someone expain attenuation to me..

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Attenuation. . .
Mar 7, 2008 10:40AM PST

is signal loss. The telephone cable pair, due to its makeup, is a capacitor. An analog signal (between 200 and 4000 Hz) and capacitance opposes any rapidly changing direction of current or change in voltage. By its nature, capacitance holds down an analog signal and attenuates (drops) the signal power level. Therefore, the greater the distance, the more capacitance, the greater the signal loss, or attenuation.

Here is a little page from my web site. It deals with dial-up speed but you might find interesting.

http://www.wayne2.net/speed.htm

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DSL SMART COILS
Mar 13, 2008 8:34PM PDT

they are supposed to be transparent to dsl and let you run it up to 30kft-haven't tried them yet but had breakfast with some big cheeses from the comp yesterday and they never heard of it and want to try it out.here is the place to check them out. http://www.charlesindustries.com/main/te_smart_coil.html

I'm a DSL tech in NC and hope they try them here. I'll keep you updated.

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(NT) Very interesting, thanks.
Mar 14, 2008 8:20PM PDT
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Yep, They work
Mar 16, 2008 8:09AM PDT

I have been installing them for about a year. They certainly allow dsl to pass but they are costly and not fun to install. We use them in conjunction with Adrenaline express units, over 24,000.

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smart coil
Mar 16, 2008 10:08AM PDT

does it help with attenuation at approx 17-18kft? we would be coming out of the CO from either a Stinger or Calix.

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smart coil
Mar 19, 2008 10:22AM PDT

You don't need load coils at 17k or 18k in my opinion. If your plant is loaded that close to the CO I would find that strange. In the past I would yank out all loads when installing dsl up to 18k ft. I have never had voice problems doing that.

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attenuation trouble
Mar 19, 2008 11:12AM PDT

we don't really have a voice issue out to 17-18k but the attenuation on those cable runs is borderline at 60+--sometimes 63 and the dsl wont run stable with that-any suggestions?

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That is pretty high at that distance
Mar 19, 2008 11:57AM PDT

I don't know why your attenuation is so high. Dsl won't sync up in our plant with anything above 63db either. I guess 59, 60, or 61 isn't really too bad at 18000 ft. I often work with Calix Dslams and If you slow the customer down in 512k increments you can usually overcome the attenuation. You probably already know that the SNR ( Signal to Noise Ratio) is the inverse of your speed. By slowing down the customer your SNR should increase and overcome the Attenuation. At 18000 ft you may have to slow the customer down to 1 meg or slower. Just remember that the rule of thumb is 8db (SNR) or higher for reliable Service. I try for 10 db that way there is a little more room for error.

P.S. The above is just how I have seen things work. Around here they just give me the equipment and I Figure it out by trial and error.

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How much bridge tap is connected?
Mar 19, 2008 9:09PM PDT

Too much will cause DSL reflection and voice attenuation.

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bridge tap
Mar 20, 2008 8:10PM PDT

i checked the loop and there is no bridge tap- i think it's just the aerial plant all the way out there-there were other orders for dsl out that way but they have been denied for now until we find a fix

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dsl sync /smart loads
Mar 28, 2008 10:43AM PDT

Please remember... longer loops, vioce have to be loaded "do a loop test!!!" smart loads will "an inductor" pass the higher hz "dsl" but balance the vioce hz. This enables the the responses to sound like me not you. If your over 60 db att. the modem probly won't sync or it will be produceing errors.. Is the dslam adsl or adsl2+? 2+ doubles the downstream rates and may have 'reach extended' more umph. Cable gague? 26 will kill you. 19,22 yoo you go. 24 4 loads + mabye another 5k' @ 1.5mbs. I've been a repair person for over 30 years, love this stuff. Just look, there are extenders, repeaters (regenators) out there. Now lets get managment to unload load extend.
test, use your meter. OP

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Bridge tap. . .
Mar 22, 2008 8:17AM PDT

How about beyond the terminal. Cut it dead to the field?

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bridge tap
Mar 22, 2008 8:30AM PDT

no bridge taps and cut dead to the field-just about 30-40 year old aerial plant

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load coils and smart coils
Jul 30, 2009 12:57PM PDT

load coils are used to tune the voice frequency by blocking frequencies out side the vf range which would include DSL frequencies. The smart coil made by Charles Industries use a built in high frequency bypass allowing the Dsl to pass and still blocking frequencies that affect the voice frequencies. They work well. Attenuation is loss of signal, the longer the loop, the more resistance to the signal and loss or attenuation. A simple loss test, using 1000hz and a loss test set should tell the quality of the cable pair.