atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Telecom Service & Providers VoIP / POTS humming problem

Hmmm. Would this indicate a bad ground on the FIOS conversion equipment? It finally gets a good ground when the soil is wet enough? John C.

This is a bit mysterious. Tell me if I understand it correctly:

1. You have a copper POTS line and a fiber POTS line.
2. When you plug the 2-line phone to both of them there is no hum

Is that right?

Disconnect everything from both lines. If there is no hum at the demarc, start hooking things up 1 at a time. When the hum begins, whatever is connected last is your culprit.

Unless he has multiple defective devices, and that may be the problem! Why didn't we think of that before? That would explain the weirdness! John C.

I have no copper - I have fiber POTS and vonage.

There has never been any hum at the demarc or at the vonage box. The interior wires didn't give me hum on any line when connected to vonage, but did give me hum on each line when on POTS. Now there is no hum on anything and everything is plugged in - fax (L1), postage meter (L1), and two line phone.

It seems like it must have been something on the Verizon system as it went away without any work on my part.

Sorry, I misunderstood. So both POTS lines are delivered through FIOS, ie you use 2 POTS jacks on the Verizon ONT.
I also assume that the Vonage equipment (ATA? VOIP router?) is connected to the router that Verizon provides with FIOS.

Is your setup as follows?

FIOS POTS L1 fax&meter
FIOS POTS L2 panasonic 2-line phone
VONAGE VOIP panasonic 2-line phone

According to your posts, hum appears when one of the POTS lines is hooked up to the phone but NOT when both of them are.
And there is no hum at all when using VOIP.

If that is the case (and the problem reappears) I'd call Verizon. It is possible that whatever is wrong on the their side becomes worse the more (analog) devices you add to the FIOS POTS lines. Not to say that the meter can't be defective.

BTW, you CAN use analog data devices over VOIP, but it's not worth the trouble or cost for a residential customer, imo.

Hum can be created in a multitude of ways, but the most common is an impedance mismatch. What we have to remember is central office lines are 100% BALANCED lines. There is no reference to ground. Neither the tip nor the ring is connected to or referenced to ground in any way. Completely isolated. Think rabbit ears on your TV antenna or speaker wires in most cars. There's just 2 wires - not grounded. But when you wanted to connect rabbit ears to a TV with a cable input - you needed to use a BALUN (BALanced to UNbalanced adapter) to connect.

Cable TV/Telephone is UN-Balanced because one side is attached to ground (the sheath), and its then converted to BALANCED inside the ATA device. Computers would also be considered unbalanced as its grounded (even the neutral is grounded in the main AC panel). In this thread (and in the thread from last year) nobody thought to check / lay blame on the Magic Jack / ATA interface. Something as simple as a messy solder joint causing a bridge from the balanced side to the unbalanced side. Computer guys are bad for this, assuming it cant be a problem with the computer interface.

Commercial phone systems are properly engineered to provide the impedance separation between lines so having lines from different providers/sources works fine on that equipment - no 'ground hum' issues because of the impedance isolation. Residential equipment is not designed for that. Basic 2 line phones are made with extremely simple bridging/mixing circuitry that does not take into account the user wanting to combine different sources. Please correct me if I'm out to lunch.

You might find filters work a little by reducing the audible effect of the mismatch, but ultimately using a non-commercial 2 line phone to mix VoIP and POTS is problematic at best.

So what can you do? Buy a used commercial phone system. Ask a local vendor for a quote to have one installed - i've put dozens of them in homes for home-offices. Use 2 single line phones that are electrically isolated completely.

I'm sure everyone here will agree - buy CHEAP, expect PROBLEMS - and this goes for hardware/software/service/telephone provider solutions/computers/cars/cell phones/VoIP/technicians/wives/husbands.

I realize this thread is old but thought there may still be some interest as I was. I just started having the hum problem with a 2-line A&T phone. I had POTS and VOIP (T-Mobile) with no problem then switched to cable (Brighthouse) and VOIP. I had all the symptoms described by others. I fixed the problem by replacing the power adapter that came with the VOIP (switching power supply) with and older style power adapter (conventional power supply with a transformer). Bigger and heavier but in this case better. Both lines are now quite. Thanks for all the posts. It really helped to know others had the same problem.

Hmmmm. Plain old analog P/S maybe a with REAL ground pin? Versus a Switcher P/S without a ground pin?