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Author Topic: Phone Line Issue w/Obi 110  (Read 33602 times)
sailing
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« Reply #20 on: September 10, 2014, 04:21:56 am »

Sorry for not responding sooner but I don't get to read the forum everyday.

The on hook voltage is irrelevant. The off hook is where the problem would lie. 70mA seems awfully high but you didn't measure the voltage during off hook. Measure voltage and current off hook with a phone. Repeat with the Obi installed, with the phone plugged into the Obi off hook.

The POTS specification is a compromise to allow few problems under almost any circumstance, such as being too close or too far from the CO. Some lines will be just outside the spec but a phone will work regardless. My thinking is your setup may be operating in this type of situation. The phone company only needs to make the lines work with phones so they know how to do that. Electronic devices are designed to work within a certain spec. Once outside of it and they may have problems.

As of a couple of years ago, the integrated circuits in the Obi110 were from Silicon Labs and probably still are. I'll see if I can get the general specs for their POTS ICs. Then the above voltage and current measurements can be compared.
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DanielG
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« Reply #21 on: September 10, 2014, 09:21:35 am »

To Ostracus - I don't know how the A/D | D/A conversion works - that's news to me.  As for the half/full duplex comment, we can unplug Ethernet all together and still have this issue for POTS calls.  It's not related to Ethernet.

To Sailing - we'll test voltage/current again, but we just had a Verizon tech onsite who tested everything and he left saying the voltage/current was within specs and there's nothing else he can do to improve it further.  Said it's totally ideal.  Let me know what you hear back on the general specs for the Obi chips.

Daniel
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Shale
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« Reply #22 on: September 10, 2014, 10:38:02 am »

Yes, it is an interesting problem. Your duplicating the problem in more than one setup makes the more obvious potential causes improbable.

I presume that your distance to your switch is fairly short. As an experiment, I would try connecting the OBi110 line port with maybe a 1 K or 470 ohm resistor in series. I understand that a balanced pair of resistors would be better, but I think that the mismatch would not introduce a significant problem in a short loop. Or use 2 resistors. That does feel more more harmonious.

You may even have a breakout box that makes this easier than locating and cutting a cable that has real copper wires and tacking a resistor or two in place.

Why do I think this is worth trying? I think it will reduce the current for one thing. I suspect that you line from the switch is much lower impedance than it would be from a central office.
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DanielG
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« Reply #23 on: September 10, 2014, 10:55:02 am »

So here are the numbers from the latest test:

No Obi:  16vdc and 70ma
With Obi: 9vdc 70ma

All measured off hook

-Daniel
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sailing
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« Reply #24 on: September 10, 2014, 05:53:58 pm »

I took a current measurement into a off hook phone on a POTS line. The current into the off hook phone was 40mA. 70mA seemed high so now I'm thinking maybe the input of the Obi is being overloaded. There is a current limit setting in the obi that limits the current to 60mA. Go into the Obi110 setup Physical Interfaces>Line Port>Port Settings. Uncheck the default for CurrentLimitingEnable and check the box to limit the current.

Another way to check this idea out is to plug one or two phones into the POTS line with the Obi. When talking into the phone plugged into the Obi, also off hook the other phones that are plugged directly into the POTS line. The other phones will shunt some of the current so the Obi will have less current to it. If the issue is too much current, then the Obi's phone should sound ok at this point.

Shale's idea with the resistors is another way to experiment but you have to choose values that will drop the current to around 40mA. 600 ohms should work although Shale's choices will work also.
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Ostracus
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« Reply #25 on: September 10, 2014, 06:17:51 pm »

Sorry for not responding sooner but I don't get to read the forum everyday.

The on hook voltage is irrelevant. The off hook is where the problem would lie. 70mA seems awfully high but you didn't measure the voltage during off hook. Measure voltage and current off hook with a phone. Repeat with the Obi installed, with the phone plugged into the Obi off hook.

The POTS specification is a compromise to allow few problems under almost any circumstance, such as being too close or too far from the CO. Some lines will be just outside the spec but a phone will work regardless. My thinking is your setup may be operating in this type of situation. The phone company only needs to make the lines work with phones so they know how to do that. Electronic devices are designed to work within a certain spec. Once outside of it and they may have problems.

As of a couple of years ago, the integrated circuits in the Obi110 were from Silicon Labs and probably still are. I'll see if I can get the general specs for their POTS ICs. Then the above voltage and current measurements can be compared.



Picture of a dead Obi110.
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DanielG
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« Reply #26 on: September 11, 2014, 06:33:59 am »

Will give that setting a try and touch back.

Daniel
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DanielG
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« Reply #27 on: September 16, 2014, 12:50:26 pm »

I tried the setting and it didn't help either.  Any other thoughts?  We are finding that this is significantly worse at one store than the rest but they all still have their occasional hiccups.

Daniel
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Shale
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« Reply #28 on: September 16, 2014, 01:11:27 pm »

Any other thoughts?
If I had suggested trying a 10 dB 600 ohm pad, instead of the resistors, would you have found that credible?
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Mango
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« Reply #29 on: September 16, 2014, 06:29:34 pm »

My POTS line also has a high loop current and I experienced similar symptoms to you.  Unfortunately, I damaged the line port - I assume permanently - on two OBi110 devices before I figured out what the problem was.  I don't know if the CurrentLimitingEnable setting would solve the problem or not.  I don't have any more OBi110 devices that are not in use and I don't want to try it on my last remaining one in case I damage it too.  If you try it on a fresh OBi110, please let us know if it solves the problem.  In that case, it would be very disappointing that this was not enabled by default.

Since installing this device, the OBi110 has performed properly: http://www.sandman.com/loop.html#LoopCurrentRegulator

The regulator auto-adjusts so if the loop current on your lines fluctuates (as mine does) things should still work properly.

If you're electrically inclined, here are some photos of the device: http://www.dslreports.com/forum/r29099727-From-now-on-I-ll-use-a-loop-current-regulator-with-my-OBi110
« Last Edit: September 16, 2014, 06:31:41 pm by Mango » Logged

sailing
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« Reply #30 on: September 17, 2014, 04:14:27 am »

I've never used nor have I read any reports about the overcurrent setting in the Obi so my suggestion was a hope that it might help. Mango's idea that too much current can damage the Obi is a possibility. If this occurred, then even if the overcurrent setting works, you will still get a distorted sound. You should try my second suggestion with the extra phones sinking some of the current. Make a call with a directly connected phone then pick up the phone connected to the Obi. You probably need to try a fresh Obi in case the old one is damaged. This approach guarantees less current to the Obi. First you need to prove too much current is the problem. Mango's suggestion of a separate current limiter may be necessary if the Obi's current limiting setting doesn't work as assumed.
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Mango
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« Reply #31 on: September 17, 2014, 09:51:26 am »

the extra phones sinking some of the current

That is interesting.  Could it be that POTS providers supply extra current on purpose so that a family could use many phones at once?
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DanielG
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« Reply #32 on: September 17, 2014, 10:14:19 am »

I just ordered one of those devices as suggested and I'll report back with what I find once it arrives (should be in on Monday).

Thanks,

Daniel
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sailing
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« Reply #33 on: September 18, 2014, 04:07:35 am »

POTS specifications are a compromise. They need the phones to work miles from the CO but if you are close to the CO, you will have higher loop current. The old phones would work under all situations and I guess the newer phones don't have a problem either. Unfortunately, a device such as the Obi, must set a limit on the upper end of the loop current.
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DanielG
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« Reply #34 on: September 22, 2014, 12:58:55 pm »

The part arrived today and I'll install it this afternoon.  Please note it may be 2-3 days before I respond again just so I wait enough time to determine if this fixes the issue or not.

-Daniel
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DanielG
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« Reply #35 on: September 23, 2014, 06:43:10 am »

Putting the device on did not work and in fact made the line completely unusable compared to usable but inconsistent as I've been experiencing all along.  Running out of options here short of punting on Obi at this store I'm afraid.  Any other thoughts?
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Mango
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« Reply #36 on: September 23, 2014, 07:03:13 am »

That is extremely curious behaviour.

You tried the loop current regulator with a new OBi, correct?  If you tried it with an old OBi, that was connected to the POTS line without the regulator, it is possible it has been permanently damaged.

With the line port off hook, did you check Status >> PHONE & LINE STATUS >> LoopCurrent to see if the regulator was connected correctly?  When things are working propelry, it should be around 25 mA.

Finally, if for testing purposes you have altered any settings under Physical Interfaces >> LINE Port >> Port Settings, you may want to return them to default.
« Last Edit: September 23, 2014, 07:04:46 am by Mango » Logged

DanielG
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« Reply #37 on: October 03, 2014, 11:50:17 am »

Yes, tried with new Obi - same results.  Yes, with line off hook, Loop Current showed correct.  And yes, testing was done with default settings for the Line port.  Still same results.
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sailing
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« Reply #38 on: October 06, 2014, 04:54:08 am »

There is something unique with your POTS/Obi setup that you may not be aware of. The phone is tolerant of it but the Obi isn't. Maybe one wire of POTS touching a ground somewhere? Or some other problem I cannot begin to guess at. Something this unique will make it impossible for anyone to give advice as to what the problem is.
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DanielG
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« Reply #39 on: October 06, 2014, 10:07:50 am »

Fair enough.  We've tried to rule all of that out and believe to have done so, but obviously we continue to have these issues.  If no one else can help, please go ahead and close this ticket and I guess I'll just have to look into something else at that store (AudioCodes box, actual Small ShoreTel switch, etc).

-Daniel
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