Persistent hum on my connected phone
jimates:
Quote from: RonR on February 23, 2011, 12:41:33 pm
Phones are not normally polarity sensitive, so reversing the Tip/Ring connections isn't likely to change anyting.
Don't know if this relates to what you just said. I haven't had a need to play with phones in a long time but at one point this mattered: If the green and red wires were reversed you would still get a dial tone, but it would not dial. pressing the button had no effect on the tone and after it timed out the recording would come on.
MichiganTelephone:
Quote from: jimates on February 23, 2011, 01:16:54 pm
Quote from: RonR on February 23, 2011, 12:41:33 pm
Phones are not normally polarity sensitive, so reversing the Tip/Ring connections isn't likely to change anyting.
Don't know if this relates to what you just said. I haven't had a need to play with phones in a long time but at one point this mattered: If the green and red wires were reversed you would still get a dial tone, but it would not dial. pressing the button had no effect on the tone and after it timed out the recording would come on.
You're both right. Newer phones are not polarity sensitive. And neither were most older phones, except some early models with touch tone dialing. In those phones, the dials got their power through a single diode rectifier which would prevent power from flowing in the "wrong" direction, which would prevent damage to the touch tone pad but also prevented dialing if tip and ring were reversed.
Later on the phone manufacturers started incorporating a bridge rectifier circuit (similar to what's used in many "wall wart" power supplies to convert AC to DC) into their touch tone pads, so no matter with side of the line was + or -, the touch tone pad would always get the correct polarity voltage. With those phones, and with newer all-electronic phones that also use bridge rectifiers in their power supplies, it should not make any difference which side is tip or ring. A phone line is supposed to be a "balanced" connection, so reversing tip and ring should not make any difference.
What happens if you connect a phone directly to the phone line and dial a single digit to "break" dial tone? Do you still hear the hum? What if you plug a phone into the test jack in the network interface device outside your home and do the same thing - do you hear the hum there? If you do, there may be "Longitudinal Imbalance" on your phone line (see this technical bulletin) and that's usually something the phone company has to fix (and yes, they do need to fix it, no matter how much "repair service" says it's not their problem - tell them you'll file a PUC/PSC complaint if they don't send someone out, and do it if you need to).
You have to realize that in the United States there is a LOT of aging copper out there, going into terminal boxes with corroded connections. Plus, in the spring of the year, you get things like spring rain coupled with the thawing of snow and ice, which can cause flooding in cable vaults and even more trouble for copper cables that in some cases are well over a half-century old. Phone companies are reluctant to do maintenance on their old copper plant because they know its useful life is limited, and we are getting closer and closer to the "tipping point" where landlines (or at least, traditional landlines from a "baby Bell" telephone company) become a thing of the past. So sometimes you have to twist their arms a little to get them to fix problems like this.
ludlow1953:
I have the hum too. Tried two different phones - one without external power supply. Both have hum on line. On two-line phone, hum transfers to line two. If I unplug the Obi, the hum goes away. Line 2 comes from a Magicjack plugged into USB, which gives clean, "no hum" dial tone and connection. Tried different phone cables between phone and Obi (2 & 4 wire) without a change. I have to believe the hum might be generated by the power supply to the Obi, but just WAG. No house wiring involved. Phone plugged directly into "Phone" jack on Obi. No "Line" in use. I have used ATAs with this phone (Vonage, phone.com, etc.) with no hum. Obi is first device to generate hum. Hmmm... :-\
MichiganTelephone:
It's possible you got a power supply with a bad capacitor or something. Contact Obihai support (email support@obihai.com) and see what they say.
Jeff205:
Even when I break dial tone, the hum is still there, but only when 2 lines are plugged in to the phone. My home phone service is actually VOIP provided by my cable provider, so even going to the box outside would not work (plus it's only when 2 lines are connected to the phone). It does not matter which line I remove, the Obi or my home service, and the hum goes away. I tried 2 and 4 wire lines as well with no success.
And do you think we both received a bad power supply?
Still can't figure this out!!!!
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