[mikefahy]

Odd problem involving USB port characteristics on laptop, battery power vs ac power.

Details.

Magicjack USB VOIP device.

2 line DECT 6.0 expandable phone. Line one plugged into telco pots line. Line 2 plugged into Magicjack.

When the laptop is on battery power, Magicjack caller id works and the phone lines are both clean with zero hum or background noise.

When the laptop is on AC power, Magicjack caller id doesn't work and line one (not the magicjack line) has a strong background hum after breaking the dial tone. Same thing when the magicjack is plugged into a desktop computer.

Unplugging Magicjack from line 2 eliminates the background hum on line one.

Obviously the USB power levels are different. My first thought is how to make a USB port on a computer running off AC power equal to the USB ports on a computer running off battery power? Or, simply stated, what's the difference?

[mjd420nova]

Welcome to PC World forums. Hum and noise on phone lines can be caused by intermittent jacks and cables. Adapters can be a source of differences in potentials between devices and can be hard to trace.

First, I don't like to use the USB ports on either the laptop or desktop to power any external devices. I use a powered USB hub on each desktop and laptop I own. Exceptions are a mouse and keyboard. These ports are prone to getting overloaded and cold solder joints with burned traces. Humming and excessive noise between phone lines and USB devices can often be traced back to the AC adapter and the loads they are being subject to.

This post has been edited by mjd420nova: 26 April 2012 - 09:27 AM

[mikefahy]

mjd420nova, on 26 April 2012 - 09:23 AM, said:

First, I don't like to use the USB ports on either the laptop or desktop to power any external devices. I use a powered USB hub on each desktop and laptop I own. Exceptions are a mouse and keyboard. These ports are prone to getting overloaded and cold solder joints with burned traces. Humming and excessive noise between phone lines and USB devices can often be traced back to the AC adapter and the loads they are being subject to.

Thanks for the response.

The desktops or AC powered laptops produce the 'other line hum' on a 2 line phone regardless of an onboard usb port, powered hub port or unpowered hub port.

This post has been edited by mikefahy: 26 April 2012 - 09:34 AM

[smax013]

mikefahy, on 26 April 2012 - 09:03 AM, said:

Odd problem involving USB port characteristics on laptop, battery power vs ac power.

Details.

Magicjack USB VOIP device.

2 line DECT 6.0 expandable phone. Line one plugged into telco pots line. Line 2 plugged into Magicjack.

When the laptop is on battery power, Magicjack caller id works and the phone lines are both clean with zero hum or background noise.

When the laptop is on AC power, Magicjack caller id doesn't work and line one (not the magicjack line) has a strong background hum after breaking the dial tone. Same thing when the magicjack is plugged into a desktop computer.

Unplugging Magicjack from line 2 eliminates the background hum on line one.

Obviously the USB power levels are different. My first thought is how to make a USB port on a computer running off AC power equal to the USB ports on a computer running off battery power? Or, simply stated, what's the difference?

Sounds like you are getting some "noise" over your power lines that is then somehow transmitting through the computer when it is pugged into wall...and that noise is crossing into the traditional line by of the MagicJack line & the two line phone. The challenge will to be to try to find the source of the "noise" and see if you can filter it.

You might want to try powering everything (in the room and maybe the house) else off except the computer and the phone and see if that helps. If it does, then try power up stuff one device at a time. When the noise returns, then you are close to figuring out what is causing the noise...but keep in mind it could actually be a combination of things. So, you might have to try powering stuff up in different sequences after you narrow down the list of possibilities of the source of the noise.

[mikefahy]

smax013, on 26 April 2012 - 10:34 AM, said:

Sounds like you are getting some "noise" over your power lines that is then somehow transmitting through the computer when it is pugged into wall...and that noise is crossing into the traditional line by of the MagicJack line & the two line phone. The challenge will to be to try to find the source of the "noise" and see if you can filter it.

You might want to try powering everything (in the room and maybe the house) else off except the computer and the phone and see if that helps. If it does, then try power up stuff one device at a time. When the noise returns, then you are close to figuring out what is causing the noise...but keep in mind it could actually be a combination of things. So, you might have to try powering stuff up in different sequences after you narrow down the list of possibilities of the source of the noise.

That's probably pretty close to a solution if I can pull it off. Take a headset and go to work in the breaker panel and see if I can narrow it down.

Better wait until I'm here by myself.

[waldojim]

mikefahy, on 26 April 2012 - 09:03 AM, said:

Odd problem involving USB port characteristics on laptop, battery power vs ac power.

Details.

Magicjack USB VOIP device.

2 line DECT 6.0 expandable phone. Line one plugged into telco pots line. Line 2 plugged into Magicjack.

When the laptop is on battery power, Magicjack caller id works and the phone lines are both clean with zero hum or background noise.

When the laptop is on AC power, Magicjack caller id doesn't work and line one (not the magicjack line) has a strong background hum after breaking the dial tone. Same thing when the magicjack is plugged into a desktop computer.

Unplugging Magicjack from line 2 eliminates the background hum on line one.

Obviously the USB power levels are different. My first thought is how to make a USB port on a computer running off AC power equal to the USB ports on a computer running off battery power? Or, simply stated, what's the difference?

There is absolutely no difference in the amount of power being supplied to the USB device. There are many rules in place for USB behavior - and that is one of them.

What it sounds like, is a ground loop hum. When you are on battery power, the voip device is effectively acting as the only grounding source, when plugged in, you create your ground loops with different resistance to ground. There are ground loop isolators out there, but I cannot remember one that actually works.

[crazy4laptops]

mikefahy, on 26 April 2012 - 09:03 AM, said:

When the laptop is on battery power, Magicjack caller id works and the phone lines are both clean with zero hum or background noise.

When the laptop is on AC power, Magicjack caller id doesn't work and line one (not the magicjack line) has a strong background hum after breaking the dial tone. Same thing when the magicjack is plugged into a desktop computer.

Unplugging Magicjack from line 2 eliminates the background hum on line one.

Obviously the USB power levels are different. My first thought is how to make a USB port on a computer running off AC power equal to the USB ports on a computer running off battery power? Or, simply stated, what's the difference?

As smax said line noise, my hunch is also with line noise. Most common sources of line noise are microwaves and audio amps. If you have any audio systems in the house, not just in the computer room, turn it off and see if your phone issues go away. The other source is a failing DSL filter, but then you'd hear it on battery too...