Noises in phone line when no phones are in use

[jayn123]

I connected my phone line to an audio mixer. When connected to the mixer,
I can hear any signals that get sent over the line, including conversations.
Mysteriously I'm noticing noises that happen when no phones are in use:

1) Every time I hang up a phone, I, almost immediately, will hear a series
of two chirps on the phone line. The tones are approximately 250ms apart
and approximately 250ms in duration. Each chirp sounds like a "dual" tone,
like maybe a type of sound a modem sometimes makes, but the prominent
frequency of the 1st chirp is roughly a C# above A=440 and the second is a
above A 440 (approximately two semitones apart, with the first being around
554hz and second being around 587.83 assuming I don't have the octave
wrong). The chirps happen every once in a while no phones are in use in
addition to happening every time the phone is hung up.

2) There are humming noises that happen virtually all the time, mainly
resembling a 60hz hum but can jump up to the next octave and vary in pitch.
The humming noises are generally lower in volume than a quiet phone
conversation.

3) Every once and a while there is a buzzing that resembles a ringer signal
albeit weaker and which doesn't always repeat at regular intervals like a
ringer signal.

4) There are buzzes that resemble a cat purring every once and a while.

5) When connected to the mixer, my phone line will often disconnect or stop
ringing after the first ring when somebody calls me...why does this happen?
(otherwise there is no interference with the phone line or DSL)

NOTE: I have DSL, but the noises happen whether or not my DSL modem is
turned on. I am monitoring from a jack that has a DSL filter connected to
it, so the DSL should be filtered out in any case.

NOTE2: The noises happen whether or not any particular phone is connected to
the phone line.

Are these normal noises, or is it likely that my phone is tapped?

Granted, I have no reason to believe anyone would want to tap my phone line
since I lead a very boring life, however since I'm not the original owner of
my house, I decided to check for "bugs" on my gray phone interface box on
the owner side of the box. None were present. I did not open the phone
company's side of the box, however.

Wondering what these noises are? Clearly the two chirps when the phone is
hung up is not just "line noise".

Thanks,

J.

 

[William R. Walsh]

Hi!

Wondering what these noises are? Clearly the two chirps when the
phone is hung up is not just "line noise".

I wonder--do you have any cordless phones on the line?

The two chirps you're hearing remind me of what I heard when I listened to
my 900MHz phones on a scanner. Each time one hit the base (e.g. put back in
the base for charging purposes), there would be a brief burst of
communication in the form of tones.

From what I've found out, this is the handset and base agreeing upon a
security code and communicating it to one another. If you're not hanging up
phones, perhaps someone with a similar phone nearby is doing so and your
cordless phone base can hear it. Or perhaps your phones rotate codes
randomly or in the presence of interference. In a heavily enough populated
area, there might not be enough frequencies and security codes available to
give each phone a unique pair.

There's only on reason I can think of that your phone line might have
conversations on it when nobody is using it...and that would be the
possibility that your cordless phone receiver drops into something of a
"listening" mode on any valid frequency...and, again, that there are lots of
cordless phones running on the same band in your area.

Not sure about the 60Hz hum, but it might be a ground loop problem. As for
the ringing type sounds, I remember someone somewhere saying that phone
companies did sometimes put test signals on the line. Do you see these
signals on a regular timetable?

Considering that mixers and phone lines really don't go together, you may be
inducing some of these strange noises when you connect the two.

William

 

[Arfa Daily]

I connected my phone line to an audio mixer. When connected to the mixer,
I can hear any signals that get sent over the line, including
conversations. Mysteriously I'm noticing noises that happen when no phones
are in use:

1) Every time I hang up a phone, I, almost immediately, will hear a
series of two chirps on the phone line. The tones are approximately
250ms apart and approximately 250ms in duration. Each chirp sounds like
a "dual" tone, like maybe a type of sound a modem sometimes makes, but the
prominent frequency of the 1st chirp is roughly a C# above A=440 and the
second is a above A 440 (approximately two semitones apart, with the first
being around 554hz and second being around 587.83 assuming I don't have
the octave wrong). The chirps happen every once in a while no phones are
in use in addition to happening every time the phone is hung up.

2) There are humming noises that happen virtually all the time, mainly
resembling a 60hz hum but can jump up to the next octave and vary in
pitch. The humming noises are generally lower in volume than a quiet phone
conversation.

3) Every once and a while there is a buzzing that resembles a ringer
signal albeit weaker and which doesn't always repeat at regular intervals
like a ringer signal.

4) There are buzzes that resemble a cat purring every once and a while.

5) When connected to the mixer, my phone line will often disconnect or
stop ringing after the first ring when somebody calls me...why does this
happen? (otherwise there is no interference with the phone line or DSL)

NOTE: I have DSL, but the noises happen whether or not my DSL modem is
turned on. I am monitoring from a jack that has a DSL filter connected to
it, so the DSL should be filtered out in any case.

NOTE2: The noises happen whether or not any particular phone is connected
to the phone line.

Are these normal noises, or is it likely that my phone is tapped?

Granted, I have no reason to believe anyone would want to tap my phone
line since I lead a very boring life, however since I'm not the original
owner of my house, I decided to check for "bugs" on my gray phone
interface box on the owner side of the box. None were present. I did not
open the phone company's side of the box, however.

Wondering what these noises are? Clearly the two chirps when the phone is
hung up is not just "line noise".

Thanks,

J.

Your phone line is always 'live' and connected to the SLIC at the exchange.
These days this is a bus-connected electronic card, and for sure, there will
be leakage out onto the line, of supervisory tones and other exchange
related control stuff that you would not normally hear. Also, your copper
pair is coming possibly miles from your exchange, and will pass by all sorts
of EM interference sources, which will induce whistles, pops and so on into
the line, which in theory is balanced, so shouldn't respond, but in
practice, seldom is, so does.

You should also consider that although the exchange equipment and modern
phones are now all electronic, the actual transmission and ringing system is
legacy, which means that it runs at the comparitively high voltage that the
original electro-mechanical phones needed to get them going. The upshot of
this is that whilst a modern phone could actually work with just a few mV of
incoming audio, in order to maintain compatibility between it, the system,
and legacy phones, it's input is deliberately attenuated such that it too
needs volts of signal to produce audio. A side effect of this, is that low
level phone company electronic signalling, which is deliberately placed on
the line by the phone company, and line induced interference, are also
attenuated by the same amount, so become insignificant at only a few mV at
your line entry.

Now consider the mixer desk that you are glueing on the end of your line.
That is intended to work with low level signals from musical instruments, or
other audio equipment, and will be sensitive to those otherwise unheard
signals, so suddenly they become audible to you.

I don't know exactly how you are isolating the line and connecting it to
this mixer, but it strikes me that you could be dicing with a big problem
here. For a start, there are several tens of volts across the line in its
idle state. This increases to around 90v peak when a ring signal appears
across the line. The SLIC at the exchange detects an off-hook condition by
looking to see when the line has been looped by a phone, and a DC current
starts to flow. If your mixer has got an electrolytic capacitor at the iput
that you are using, when you hit it with the 90v ring signal, there will
likely be a substantial leakage current through the input circuit. The SLIC
may well see this as a looped line condition, and remove the ring signal,
hence the reason that you get one ring and no more. When the ring signal is
removed, the current in the input circuit of the mixer, will cease again,
and the SLIC will drop the call, believing that the 'phone' has been
replaced on hook.

I think that you should seriously consider what you are doing here. The
large levels of voltage that are present in the phone system, particularly
the ring signal, are highly likely to ultimately cause damage to the mixer
input circuitry. Also, it is causing a problem with your phone calls.
Another possibility is that the exchange's routiners, which scan the
subscriber lines for faults, may well pick up the "odd" impedance that this
set up is like to be placing across your line, as a fault, that may get
flagged as one for a serviceman to come and check. Phone companies also
frown on unauthorised connections to their lines, which might result in an
unbalance, and they get particularly upset about connection of
non-galvanically isolated equipment that runs from household power, due to
the potential danger that it could represent to their linemen, in the event
of a failure that placed household voltage on the phone line.

Arfa

 

[hr(bob) [email protected]]

Your phone line is always 'live' and connected to the SLIC at the exchange.
These days this is a bus-connected electronic card, and for sure, there will
be leakage out onto the line, of supervisory tones and other exchange
related control stuff that you would not normally hear. Also, your copper
pair is coming possibly miles from your exchange, and will pass by all sorts
of EM interference sources, which will induce whistles, pops and so on into
the line, which in theory is balanced, so shouldn't respond, but in
practice, seldom is, so does.

You should also consider that although the exchange equipment and modern
phones are now all electronic, the actual transmission and ringing system is
legacy, which means that it runs at the comparitively high voltage that the
original electro-mechanical phones needed to get them going. The upshot of
this is that whilst a modern phone could actually work with just a few mV of
incoming audio, in order to maintain compatibility between it, the system,
and legacy phones, it's input is deliberately attenuated such that it too
needs volts of signal to produce audio. A side effect of this, is that low
level phone company electronic signalling, which is deliberately placed on
the line by the phone company, and line induced interference, are also
attenuated by the same amount, so become insignificant at only a few mV at
your line entry.

Now consider the mixer desk that you are glueing on the end of your line.
That is intended to work with low level signals from musical instruments, or
other audio equipment, and will be sensitive to those otherwise unheard
signals, so suddenly they become audible to you.

I don't know exactly how you are isolating the line and connecting it to
this mixer, but it strikes me that you could be dicing with a big problem
here. For a start, there are several tens of volts across the line in its
idle state. This increases to around 90v peak when a ring signal appears
across the line. The SLIC at the exchange detects an off-hook condition by
looking to see when the line has been looped by a phone, and a DC current
starts to flow. If your mixer has got an electrolytic capacitor at the iput
that you are using, when you hit it with the 90v ring signal, there will
likely be a substantial leakage current through the input circuit. The SLIC
may well see this as a looped line condition, and remove the ring signal,
hence the reason that you get one ring and no more. When the ring signal is
removed, the current in the input circuit of the mixer, will cease again,
and the SLIC will drop the call, believing that the 'phone' has been
replaced on hook.

I think that you should seriously consider what you are doing here. The
large levels of voltage that are present in the phone system, particularly
the ring signal, are highly likely to ultimately cause damage to the mixer
input circuitry. Also, it is causing a problem with your phone calls.
Another possibility is that the exchange's routiners, which scan the
subscriber lines for faults, may well pick up the "odd" impedance that this
set up is like to be placing across your line, as a fault, that may get
flagged as one for a serviceman to come and check. Phone companies also
frown on unauthorised connections to their lines, which might result in an
unbalance, and they get particularly upset about connection of
non-galvanically isolated equipment that runs from household power, due to
the potential danger that it could represent to their linemen, in the event
of a failure that placed household voltage on the phone line.

Arfa

Arfa is right, be careful what you do to the phone company line. I
designed several central office test line circuits in my years at Bell
Labs. One circuit was used to detect false power crosses and grounds
on subscriber lines, and put fairly high voltages out onto the
subscriber lines when the central office was suspicious of a line
problem. Also the 90VAC ringing signal has a peak voltage of about 125
volts and can give you a very nasty surprise if you happen to be
touching the line when the phone is either ringing or perhaps being
tested because they sense something abnormal about the line.

H. R.(Bob) Hofmann

 

[jayn123]

Thanks for the replies.

To be clear, I was NOT hearing conversations EXCEPT when the phone was IN
use. However, the NOISES I was hearing were when the phone was NOT in use.

I do have cordless phones but I believe the chirping tones were still was
happening even if I disconnected those phones from the phone jacks.

Since this was interfering with the ability of the phone to ring, I've
abandoned the idea of connecting the phone line itself DIRECTLY to an audio
mixer, and decided to go to Radio Shack and invest $30 in a "Multi-Phone
Telephone recorder." This device, so far, appears to do the job of letting
me INDIRECTLY connect the phone line to the mixer, or audio recorder, and
the device says it complies with FCC specs. The device has a small output
cord with an 1/8" plug that will plug into an audio recorder or mixer, and a
2nd cord has a plug that will plug into a remote jack of an audio recorder
if the recorder has one. I'm just using the audio signal cord and not any
remote.

Presumably the use of the Radio Shack device should be much safer/reliable
way to connect the phone line to the mixer than simply taking the red and
green phone wires and directly connecting them to an audio cable with a 1/4"
plug and then plugging that into the mixer, which is the method I was using
up until I bought the Radio Shack device.

Thanks,

J.

 

[jayn123]

Oops...to be clear, the Radio Shack device is not a recorder, but a
controller used to connect the phone line to a recorder.

J.

 

[jayn123]

I was concerned about ringer voltage when I was connecting to the mixer
directly, but the ringer signal did not fry the mixer. Maybe it's because I
had so many phones connected to the line that they absorbed some of the
voltage. But, obviously there WAS a problem with my setup, since the
ringing was being stopped (maybe by the phone company) after the first ring.

<<Also the 90VAC ringing signal has a peak voltage of about 125
volts and can give you a very nasty surprise if you happen to be
touching the line when the phone is either ringing or perhaps being
tested because they sense something abnormal about the line>>

Thanks,

J.

 

[James Sweet]

Presumably the use of the Radio Shack device should be much safer/reliable
way to connect the phone line to the mixer than simply taking the red and
green phone wires and directly connecting them to an audio cable with a 1/4"
plug and then plugging that into the mixer, which is the method I was using
up until I bought the Radio Shack device.

Yikes, the first time the phone rings while plugged into the mixer
you'll probably be buying a new mixer, any method is better than
connecting it directly like that.

 

[jayn123]

<<Yikes, the first time the phone rings while plugged into the mixer
you'll probably be buying a new mixer, any method is better than
connecting it directly like that.>>

Well the phone rang many times and did not fry the mixer. Actually I tried
two different mixers and neither got fried. But I agree that something was
wrong with my setup since it often caused the phone to stop ringing after
the first ring.

J.

 

[James Sweet]

<<Yikes, the first time the phone rings while plugged into the mixer
you'll probably be buying a new mixer, any method is better than
connecting it directly like that.>>

Well the phone rang many times and did not fry the mixer. Actually I tried
two different mixers and neither got fried. But I agree that something was
wrong with my setup since it often caused the phone to stop ringing after
the first ring.

J.

Perhaps the mixers had MOVs or other input protection. The ring signal
is something in the neighborhood of 90V, an audio signal tops out around
1.5V.

 

[Arfa Daily]

Thanks for the replies.

To be clear, I was NOT hearing conversations EXCEPT when the phone was IN
use. However, the NOISES I was hearing were when the phone was NOT in
use.

I do have cordless phones but I believe the chirping tones were still was
happening even if I disconnected those phones from the phone jacks.

Since this was interfering with the ability of the phone to ring, I've
abandoned the idea of connecting the phone line itself DIRECTLY to an
audio mixer, and decided to go to Radio Shack and invest $30 in a
"Multi-Phone Telephone recorder." This device, so far, appears to do the
job of letting me INDIRECTLY connect the phone line to the mixer, or audio
recorder, and the device says it complies with FCC specs. The device has
a small output cord with an 1/8" plug that will plug into an audio
recorder or mixer, and a 2nd cord has a plug that will plug into a remote
jack of an audio recorder if the recorder has one. I'm just using the
audio signal cord and not any remote.

Presumably the use of the Radio Shack device should be much safer/reliable
way to connect the phone line to the mixer than simply taking the red and
green phone wires and directly connecting them to an audio cable with a
1/4" plug and then plugging that into the mixer, which is the method I was
using up until I bought the Radio Shack device.

Thanks,

J.

Yes, that's the way to go. This device probably has a REN of less than 1,
and will only be seen by the phone company as another electronic phone, if
they can see it at all. It will have a "phone-like" front end which provides
the isolation out to the phone line from the mixer, and also the other way
to the mixer. It will also contain circuitry which absorbs the ring voltage
( for that device alone ), making use of it to provide the cassette recorder
control output, and finally, an attenuator to provide the correct level for
a low-level input device such as a mixer or amplifier.

Arfa

 

[hr(bob) [email protected]]

Thanks for the replies.

To be clear, I was NOT hearing conversations EXCEPT when the phone was IN
use. However, the NOISES I was hearing were when the phone was NOT in use.

I do have cordless phones but I believe the chirping tones were still was
happening even if I disconnected those phones from the phone jacks.

Since this was interfering with the ability of the phone to ring, I've
abandoned the idea of connecting the phone line itself DIRECTLY to an audio
mixer, and decided to go to Radio Shack and invest $30 in a "Multi-Phone
Telephone recorder." This device, so far, appears to do the job of letting
me INDIRECTLY connect the phone line to the mixer, or audio recorder, and
the device says it complies with FCC specs. The device has a small output
cord with an 1/8" plug that will plug into an audio recorder or mixer, and a
2nd cord has a plug that will plug into a remote jack of an audio recorder
if the recorder has one. I'm just using the audio signal cord and not any
remote.

Presumably the use of the Radio Shack device should be much safer/reliable
way to connect the phone line to the mixer than simply taking the red and
green phone wires and directly connecting them to an audio cable with a 1/4"
plug and then plugging that into the mixer, which is the method I was using
up until I bought the Radio Shack device.

Thanks,

J.

Remeber, it is illegal to record a teleone message without the consent
of all prties to the conversation unless you have a court warrant to do
so. You can directly listen to the conversation(eavesdrop) but cannot
repeat what you have heard.

H. R. Hofmann

 

[hr(bob) [email protected]]

Thanks for the replies.

To be clear, I was NOT hearing conversations EXCEPT when the phone was IN
use. However, the NOISES I was hearing were when the phone was NOT in use.

I do have cordless phones but I believe the chirping tones were still was
happening even if I disconnected those phones from the phone jacks.

Since this was interfering with the ability of the phone to ring, I've
abandoned the idea of connecting the phone line itself DIRECTLY to an audio
mixer, and decided to go to Radio Shack and invest $30 in a "Multi-Phone
Telephone recorder." This device, so far, appears to do the job of letting
me INDIRECTLY connect the phone line to the mixer, or audio recorder, and
the device says it complies with FCC specs. The device has a small output
cord with an 1/8" plug that will plug into an audio recorder or mixer, and a
2nd cord has a plug that will plug into a remote jack of an audio recorder
if the recorder has one. I'm just using the audio signal cord and not any
remote.

Presumably the use of the Radio Shack device should be much safer/reliable
way to connect the phone line to the mixer than simply taking the red and
green phone wires and directly connecting them to an audio cable with a 1/4"
plug and then plugging that into the mixer, which is the method I was using
up until I bought the Radio Shack device.

Thanks,

J.

Remeber, it is illegal to record a telephone message without the
consent of all prties to the conversation unless you have a court
warrant to do so. You can directly listen to the
conversation(eavesdrop) but cannot repeat what you have heard.

H. R. Hofmann

 

[Bob Shuman]

Arfa,

Nice summary. I agree with nearly everything you wrote, except, that in
the US, the ringing voltage can actually be considerably higher than 90V
peak since the legacy Telco spec calls for "less than 100VAC RMS" (more
typically 40-75V RMS as you have stated).

This translates to a "peak" of 141 volts across the incoming tip and ring.
Also, since there is always a nominal -48VDC (-52VDC maximum) bias/battery,
the absolute peak voltage relative to earth ground can actually reach -193
volts (-52VDC - 141 volts peak)!

Bob

 

[Arfa Daily]

Arfa,

Nice summary. I agree with nearly everything you wrote, except, that in
the US, the ringing voltage can actually be considerably higher than 90V
peak since the legacy Telco spec calls for "less than 100VAC RMS" (more
typically 40-75V RMS as you have stated).

This translates to a "peak" of 141 volts across the incoming tip and ring.
Also, since there is always a nominal -48VDC (-52VDC maximum)
bias/battery, the absolute peak voltage relative to earth ground can
actually reach -193 volts (-52VDC - 141 volts peak)!

Bob

Bob, you are quite right - fingers running, brain out of gear - I must be
getting old ... !! 90 volts ring signal was the figure in my head, but that
is of course, as you say AC RMS max spec, not peak. Thanks for putting me
straight d;~}

Arfa

 

[Bob Shuman]

Hello Bob,

The line isolation circuit card that you designed wasn't the ALIT (5ESS
Circuit Packs TN138, TN139, and TN140 as I recall) was it? I just have to
ask since I was a very young Western Electric factory engineer way back when
the Bell System actually existed and manufactured their own stuff. I wrote
the factory functional circuit tests for that card! As I recall, it was one
of the first to use the (then brand new) Intel 16-bit 8086 microprocessor,
but still used a whole lot of mechanical relays to connect the Metallic
Service Unit to the customer line under test in the Line Unit.

Bob Shuman - Who is one of the few still working at the Network
Software Center/Indian Hill complex over a quarter of a century and three
company names/corporate logos later!

 

[hr(bob) [email protected]]

Hello Bob,

The line isolation circuit card that you designed wasn't the ALIT (5ESS
Circuit Packs TN138, TN139, and TN140 as I recall) was it? I just have to
ask since I was a very young Western Electric factory engineer way back when
the Bell System actually existed and manufactured their own stuff. I wrote
the factory functional circuit tests for that card! As I recall, it was one
of the first to use the (then brand new) Intel 16-bit 8086 microprocessor,
but still used a whole lot of mechanical relays to connect the Metallic
Service Unit to the customer line under test in the Line Unit.

Bob Shuman - Who is one of the few still working at the Network
Software Center/Indian Hill complex over a quarter of a century and three
company names/corporate logos later!

I designed the power cross detector for Nos 1 and 2 ESS, also the line
switching frame and ferrod scanners for 1 and 2 ESS way back in the
1960's. As a result of my discovering the source of interference to
car radios when thay parked in the parking lot at Succasunna and later
at Oswego, I eventually got into electromagnetic compatibility full
time and supervised the EMC group at Indian Hill/Naperville, IL, and
also chaired the Lucent Corporate EMC COmmittee. Retired in July 2001.
Still doing IEEE and ANSI C63 EMC standards work, teaching a little and
skiing and mountain climbing as much as II cna find time for.

H, R.(Bob) Hofmann