Getting matching transformer from telephone

[Floyd L. Davidson]

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
"Floyd L. Davidson" wrote:

The PSTN is specified from 400 to 2800 Hz, with 24 dB SNR.

By WHOM ?

ITU-T standards and Bellcore standards.

Bell don't count as they're not International.

But they do define the PSTN.

Since everyone else says ITU-T say 300-3400Hz I suspect we're seeing
another case of you being stuck in a time warp.

Explain how you are going to provide POTS service on a
metallic pair to a subscriber that is more than 5 miles
from the CO, and still get 300-3400 Hz bandwidth?

Then explain how one can connect two such circuits
together and still maintain 300-3400 Hz bandwidth.

If I'm "stuck", it's in reality.

Once again, look up the ITU-T V.32 and V.34 standards to
see what the minimum requirements are for a modem that
will work over a minimally specified PSTN connection.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[Jamie]

Eeyore wrote:

Ross Herbert wrote:


Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
:
:A proper 600:600 transformer will be more expensive than a 10k:10k one too.
:
That may be true but how many readily available 10K:10K audio transformers have
a 3.5Kv isolation rating?


I believe this was required IIRC for only brief use. He could avoid using it during
thunderstorms too.
Why? That takes the fun out of it!

http://webpages.charter.net/jamie_5"

 

[Phil McKerracher]

"Floyd L. Davidson" <floyd@apaflo.com> wrote in message
news:87zli06e7q.fld@apaflo.com...

Explain how you are going to provide POTS service on a
metallic pair to a subscriber that is more than 5 miles
from the CO, and still get 300-3400 Hz bandwidth?

Then explain how one can connect two such circuits
together and still maintain 300-3400 Hz bandwidth.

True - and by the same token, you can often get much MORE than 300-3400 Hz
through a given connection. These bandwidths are really only relevant for
trunk systems where they are restricted for economic reasons (to get as many
channels as possible down the link) and to prevent crosstalk.

As others have pointed out, the 300-3400 Hz figure is indeed the nominal
bandwidth of PSTN connections in the UK (at the 3dB points) and this is the
uk.telecom newsgroup so I think it's fair to quote that here. If you're
dialling a phone in Alaska your mileage may indeed vary.

Once again, look up the ITU-T V.32 and V.34 standards to
see what the minimum requirements are for a modem that
will work over a minimally specified PSTN connection.

I've checked both of these and they only talk about carrier frequencies,
which is not at all the same thing as "what will work over a minimally
specified PSTN connection" in Alaska! Indeed, they contain specific
procedures for dropping back to lower data rates over poor connections.

--
Phil McKerracher
www.mckerracher.net

 

[Phil McKerracher]

"Floyd L. Davidson" <floyd@apaflo.com> wrote in message
news:87zli06e7q.fld@apaflo.com...

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
"Floyd L. Davidson" wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
"Floyd L. Davidson" wrote:

The PSTN is specified from 400 to 2800 Hz, with 24 dB SNR.

By WHOM ?

ITU-T standards and Bellcore standards.

Bell don't count as they're not International.

But they do define the PSTN.

Have a look at P.310 "Transmission characteristics for telephone
band (300-3400 Hz) digital telephones" and the related specifications it
quotes then:
http://www.itu.int/rec/T-REC-P.310-200303-I/en

--
Phil McKerracher
www.mckerracher.net

 

[Floyd L. Davidson]

"Phil McKerracher" <usenet@mckerracher.net> wrote:

"Floyd L. Davidson" <floyd@apaflo.com> wrote in message
news:87zli06e7q.fld@apaflo.com...
Explain how you are going to provide POTS service on a
metallic pair to a subscriber that is more than 5 miles
from the CO, and still get 300-3400 Hz bandwidth?

Then explain how one can connect two such circuits
together and still maintain 300-3400 Hz bandwidth.

True - and by the same token, you can often get much MORE than 300-3400 Hz
through a given connection. These bandwidths are really only relevant for
trunk systems where they are restricted for economic reasons (to get as many
channels as possible down the link) and to prevent crosstalk.

As others have pointed out, the 300-3400 Hz figure is indeed the nominal
bandwidth of PSTN connections in the UK (at the 3dB points) and this is the
uk.telecom newsgroup so I think it's fair to quote that here. If you're
dialling a phone in Alaska your mileage may indeed vary.

It is *not* the "nominal bandwidth of PSTN connections".
There is no such thing specified (doing so would be
meaningless).

There are minimum bandwidth specifications for a variety
of things, such as trunks, local loops, trans-switching
system, etc. There is also a minimal bandwidth
specification for a "voice grade line" and for a
connection between two such lines, and for the allowed
distribution of loss across such a connection.

Indeed though, such specifications are *targets* and in
fact a telco is allowed to install and provide service
over a local loop that doesn't even meet those minimum
specifications. (Tariffs typically specify a percentage
of loops that are allowed to be out of out of specs.)

Once again, look up the ITU-T V.32 and V.34 standards to
see what the minimum requirements are for a modem that
will work over a minimally specified PSTN connection.

I've checked both of these and they only talk about carrier frequencies,

See sections "5.1 Data signalling rates", "5.2 Symbol
rates", "5.3 Carrier frequencies", and "5.4.1 Transmit
spectrum specifications".

They define carriers for specific symbols rates, which
is a definition of bandwidth.

V.34 defines its lowest bit rate (2400 symbols per
second) with a carrier frequency of 1600 Hz. That is a
bandwidth of 400-2800 Hz.

which is not at all the same thing as "what will work over a minimally
specified PSTN connection" in Alaska!

That is indeed *exactly* what the Standard defines.

Indeed, they contain specific
procedures for dropping back to lower data rates over poor connections.

Right on down to... "a minimally specified PSTN
connection", in Alaska and elsewhere.

I would note that it is quite possible in many locations
to have both local loops and Inter-exchange trunks that
do not meet the minimally PSTN specifications. Any
number of cable carrier systems that do not use a full
64kbps D0 PCM channel (whether it is compressed, or is
32kbps, or whatever) do not provide sufficient bandwidth
and SNR to allow a V.34 modem to maintain a connection.

Worse yet, any attempt to tandem two such facilities
will result in a connect that might not even be able to
make a connection using any of the various rates
specified by v.32!

Hence, while the PSTN is specified for 400-3200 Hz with
a minimum 24 dB SNR, that is not a guarantee.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[Floyd L. Davidson]

"Phil McKerracher" <usenet@mckerracher.net> wrote:

"Floyd L. Davidson" <floyd@apaflo.com> wrote:

Bell don't count as they're not International.

But they do define the PSTN.

Have a look at P.310 "Transmission characteristics for telephone
band (300-3400 Hz) digital telephones" and the related specifications it
quotes then:
http://www.itu.int/rec/T-REC-P.310-200303-I/en

That doesn't define the PSTN, or even come close. It defines
*digital telephones*.

Of course, even then... take a look at "Figure 2/P.310
- Receiving mask". You'll notice they are not graphing
a standard +/- 3 dB bandwidth plot, but rather a +2 to
-9 dBm plot. You might also notice that given the data
they do have, you can actually plot one!

400-2800 Hz, at +/- 3 dB.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[Floyd L. Davidson]

floyd@apaflo.com (Floyd L. Davidson) wrote:

Hence, while the PSTN is specified for 400-3200 Hz with
a minimum 24 dB SNR, that is not a guarantee.

That is a typo of course. 400-2800 Hz.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[Phil McKerracher]

"Floyd L. Davidson" <floyd@apaflo.com> wrote in message
news:87tz873zg4.fld@apaflo.com...

"Phil McKerracher" <usenet@mckerracher.net> wrote:

I've checked both of [V.32 and V.34] and they only talk about carrier
frequencies,
which is not at all the same thing as "what will work over a minimally
specified PSTN connection" in Alaska...

That is indeed *exactly* what the Standard defines.

No, that's your inference and I believe it to be incorrect
(internationally). I'm looking for an international standard that defines
the PSTN bandwidth to be something other than 300-3400 Hz.

--
Phil McKerracher
www.mckerracher.net

 

[Floyd L. Davidson]

"Phil McKerracher" <usenet@mckerracher.net> wrote:

"Floyd L. Davidson" <floyd@apaflo.com> wrote in message
news:87tz873zg4.fld@apaflo.com...
"Phil McKerracher" <usenet@mckerracher.net> wrote:

I've checked both of [V.32 and V.34] and they only
talk about carrier frequencies,
which is not at all the same thing as "what will work over a minimally
specified PSTN connection" in Alaska...

That is indeed *exactly* what the Standard defines.

No, that's your inference and I believe it to be incorrect
(internationally).

You claim the v.32 and v.34 standards only talk about
carrier frequencies, and that is clearly incorrect.

You didn't even see the 400-2800 Hz bandwidth defined in
the V.34 standard, so how likely are you to realize what
the significance of these standards are?

I'm looking for an international standard that defines
the PSTN bandwidth to be something other than 300-3400 Hz.

You haven't shown where the PSTN is defined as 300-3400
Hz, but have shown where a *digital* telephone (as
opposed to an analog set) should have +2 to -7 dB
response over 300-3400 Hz (and is expected to have 3 dB
rolloff at about 400-2800 Hz).

And the v.34 specification clearly defines the PSTN as
2400 Hz bandwidth, minimum.

You might note also that G.726, which describes ADPCM
states straight out that v.34 modems will not function,
but that modem standards using less than 2400 symbols
per second will work. As I've noted, the PSTN may have
a target of 400-2800 Hz, but there is no guarantee that
it will be even that. It absolutely is NOT defined at
anything near 300-3400 Hz!

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[tony sayer]

In article <e-ednbaP3r5b8PvUnZ2dnUVZ_jSdnZ2d@earthlink.com>, Wecan do it
<WeCanDoit@nospam.com> scribeth thus

"tony sayer" <tony@bancom.co.uk> wrote in message
news:Z0n1zqQBseZJFw3z@bancom.co.uk...
In article <foiam451b5qv851h5ko7702391hgu63732@4ax.com>,
Ross Herbert
rherber1@bigpond.net.au> scribeth thus
On Wed, 07 Jan 2009 06:52:48 -0900, floyd@apaflo.com (Floyd
L. Davidson) wrote:

:John Livingston <null@spambin.com> wrote:
:
:>Good, accurate stuff, Ross.
:
:All of it referenced the specifications for individual
:channels on various facilities. None of it had to do
:with the overall minimum allowed specification for an
:end to end connection via the PSTN.

Hold it, that's a dumb statement.

The ITU recommendation for international VF channel
bandwidth is 300-3400Hz, so
why would it be necessary to "allow a minimum" bandwidth of
400-2800Hz? If the
300-3400Hz applies to ALL channels used in an end-to-end
international link,
then it follows that the overall bandwidth is 300-3400Hz.

Ummmm... those figures are not -quite- that meaningful
unless we have
some sort of reference level ..

i.e. 300 to 3400 +/- ? dB ...



Obviously the ITU spec is greater than the so-called
"minimum" of 400-2800Hz, so
it is not necessary to "allow a minimum" bandwidth of less
than this.

The fact that some administrations may not have adopted the
ITU recommendation
and continue to use 400-2800Hz simply means that they are
not prepared to
upgrade their equipment and are therefore behind the times.
Any communication
carried over such links will mean the overall bandwidth is
degraded even if some
sections do conform to the ITU recommendation of 300-3400Hz.

:
:>I really don't know where Floyd L. Davidson is coming
from.
:
:More than three decades in the long distance
:telecommuncations industry (but not with the Bell
:System).

And I have 37 years of Telco experience from 56 - 93 in both
metro and long-line
installations. In all those years we used 300-3400Hz.


--
Tony Sayer



What do you suppose happens to the bandwidth of a signal as it
is passed through successive audio devices that are band
limited to 300-3400 Hz?

Would you expect to get 300-3400Hz +- ndB response in an end
to end loopback test when you use white noise as the test
signal? (n =ITU spec)

Going from a handset to a PBX to MUX to a CO into the network
and back if each device has a 300-3400Hz response the looped
back signal should be more band limited than the first device
in the signal chain with 300-3400Hz response originating test
signal by quite some bit.


Peace
dawg

Well either over long or local circuits -some- level reference needs be
quoted .....
--
Tony Sayer

 

[Phil McKerracher]

"Floyd L. Davidson" <floyd@apaflo.com> wrote in message
news:87priv2d08.fld@apaflo.com...

You didn't even see the 400-2800 Hz bandwidth defined in
the V.34 standard...

That's a modem standard, not a network standard. It doesn't say anything
about the PSTN bandwidth.

You haven't shown where the PSTN is defined as 300-3400
Hz, but have shown where a *digital* telephone (as
opposed to an analog set) should have...

Fair comment, but the title "Transmission characteristics for telephone band
(300-3400 Hz) digital telephones" should give you a clue.

Anyway, I've found the one that seems most relevant: G.120 "International
telephone connections and circuits - General characteristics of national
systems forming part of international connections"
(http://www.itu.int/rec/T-REC-G.120-199812-I/en) states in section 5:

"...The circuit performance objectives for attenuation distortion of
international circuits and national extension circuits were originally
selected so that acceptable performance would be obtained on analogue 4-wire
chains of up to 12 circuits. Although it is recognized that the network is
continuing its evolution to an all digital network, it is recommended that
the individual equipment network performance objectives as presented in the
following Recommendations not be relaxed: G.232 (which gives equipment
design objectives for analogue 12-channel terminal equipments); G.712 (which
gives equipment design objectives for digital PCM channelizing equipments);
and Q.552 and Q.553 (which give equipment design objectives for digital
switches).

It follows from the Recommendations mentioned above that, as a rule, the
frequency band effectively transmitted by a telephone circuit, according to
the definition adopted by the ITU-T (i.e. the band in which the attenuation
distortion does not exceed 9 dB compared with the value for 1020 Hz), will
be a little wider than the 300-3400 Hz band, and for a single pair of
channel terminal equipments of this type, the attenuation distortion at 300
Hz and 3400 Hz should never exceed 3 dB and in a large number of equipments
should not average more than 1.7 dB. It is recommended that all channel
terminal equipments, including digital switches with analogue interfaces, be
designed such that they can comply with the line-up limits specified in
Figure 1...."

And Figure 1 clearly shows a 300-3400 Hz bandwidth. Similarly there are
several figures in G.712 that show the same thing.

If you have more relevant specs, let's see them.

--
Phil McKerracher
www.mckerracher.net

 

[Floyd L. Davidson]

"Phil McKerracher" <usenet@mckerracher.net> wrote:

"Floyd L. Davidson" <floyd@apaflo.com> wrote in message
news:87priv2d08.fld@apaflo.com...
You didn't even see the 400-2800 Hz bandwidth defined in
the V.34 standard...

That's a modem standard, not a network standard. It doesn't say anything
about the PSTN bandwidth.

Yes it does. The v.34 modem protocol was specifically
designed to function over a minimally specified voice
grade dialup connection.

You haven't shown where the PSTN is defined as 300-3400
Hz, but have shown where a *digital* telephone (as
opposed to an analog set) should have...

Fair comment, but the title "Transmission characteristics for telephone band
(300-3400 Hz) digital telephones" should give you a clue.

And just how is it supposed to do that? It's a
*digital* telephone set, it doesn't even use a VF cable
loop.

Anyway, I've found the one that seems most relevant: G.120 "International
telephone connections and circuits - General characteristics of national
systems forming part of international connections"
(http://www.itu.int/rec/T-REC-G.120-199812-I/en) states in section 5:

"...The circuit performance objectives for attenuation distortion of
international circuits and national extension circuits were originally
selected so that acceptable performance would be obtained on analogue 4-wire
chains of up to 12 circuits. Although it is recognized that the network is
continuing its evolution to an all digital network, it is recommended that
the individual equipment network performance objectives as presented in the
following Recommendations not be relaxed: G.232 (which gives equipment
design objectives for analogue 12-channel terminal equipments); G.712 (which
gives equipment design objectives for digital PCM channelizing equipments);
and Q.552 and Q.553 (which give equipment design objectives for digital
switches).

It follows from the Recommendations mentioned above that, as a rule, the
frequency band effectively transmitted by a telephone circuit, according to
the definition adopted by the ITU-T (i.e. the band in which the attenuation
distortion does not exceed 9 dB compared with the value for 1020 Hz), will
be a little wider than the 300-3400 Hz band,

Since "bandwidth" is measured at the 3 dB points, which
would clearly be significantly less than 300-3400 Hz,
all you are demonstrating is that the claimed 300-3400
Hz bandwidth *cannot* be valid as the minimum
specification for an end to end connect. That is
particularly true give that the above refers to
individual *channels*, and does not include the local
loop, which might just be 3 to 5 miles of 26 gauge
cable.

and for a single pair of
channel terminal equipments of this type, the attenuation distortion at 300
Hz and 3400 Hz should never exceed 3 dB and in a large number of equipments
should not average more than 1.7 dB. It is recommended that all channel
terminal equipments, including digital switches with analogue interfaces, be
designed such that they can comply with the line-up limits specified in
Figure 1...."

And Figure 1 clearly shows a 300-3400 Hz bandwidth. Similarly there are
several figures in G.712 that show the same thing.

If you have more relevant specs, let's see them.

I've already provided them. And clearly *that* one is
not pertinent.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[Mark Evans]

In uk.telecom Stuart <Spambin@argonet.co.uk> wrote:

In article <495EF5C0.E2464EA4@hotmail.com>,
Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

It is always grounded, directly or indirectly, otherwise the screen fails
to be effective.

It certainly isn't used to provide phantom power under ANY circumstances.

So how does phantom power work then? You stick a voltage down the signal
leads in parallel and the the return is via what?

One signal lead is connected to positive the other signal lead is
connected to negative. Much the same way as telephones are powered.
For screening to work it must not be carrying an electrical current.

 

[Floyd L. Davidson]

Mark Evans <mpe@anacon.freeserve.co.uk> wrote:

In uk.telecom Stuart <Spambin@argonet.co.uk> wrote:
In article <495EF5C0.E2464EA4@hotmail.com>,
Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

It is always grounded, directly or indirectly, otherwise the screen fails
to be effective.

It certainly isn't used to provide phantom power under ANY circumstances.

So how does phantom power work then? You stick a voltage down the signal
leads in parallel and the the return is via what?

One signal lead is connected to positive the other signal lead is
connected to negative. Much the same way as telephones are powered.
For screening to work it must not be carrying an electrical current.

In the context presented, that is generally true... but
I'd like to point out that the shielding on multipair
telephone cables is 1) grounded, 2) commonly conducts
current, and 3) the noise reduction provided is
*enhanced* by the current!

Both ends of the cable are well grounded and any induced
current in the shield will be greater than in any
individual cable pair. The current in the shield
induces an opposite current into the cable pair, thus
reducing the total noise signal in each pair.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com

 

[tony sayer]

In article <87bptwsha8.fld@apaflo.com>, Floyd L. Davidson
<floyd@apaflo.com> scribeth thus

Mark Evans <mpe@anacon.freeserve.co.uk> wrote:
In uk.telecom Stuart <Spambin@argonet.co.uk> wrote:
In article <495EF5C0.E2464EA4@hotmail.com>,
Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:

It is always grounded, directly or indirectly, otherwise the screen fails
to be effective.

It certainly isn't used to provide phantom power under ANY circumstances.

So how does phantom power work then? You stick a voltage down the signal
leads in parallel and the the return is via what?

One signal lead is connected to positive the other signal lead is
connected to negative. Much the same way as telephones are powered.
For screening to work it must not be carrying an electrical current.

In the context presented, that is generally true... but
I'd like to point out that the shielding on multipair
telephone cables is 1) grounded, 2) commonly conducts
current, and 3) the noise reduction provided is
*enhanced* by the current!

Both ends of the cable are well grounded and any induced
current in the shield will be greater than in any
individual cable pair. The current in the shield
induces an opposite current into the cable pair, thus
reducing the total noise signal in each pair.

Do you manage to get grounds in that soil over there, seemed to think it
was more permafrost..

Those pix on the Floyd website look rather, well "cool" ...
--
Tony Sayer

 

[Michael A. Terrell]

tony sayer wrote:

Do you manage to get grounds in that soil over there, seemed to think it
was more permafrost..

Try driving a 60 foot ground rod through permafrost some time.



--
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aioe.org, Goggle Groups, and Web TV users must request to be white
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There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

 

[Stuart]

The OPs problem can be solved by using the circuit from p62 of Elektor
magazine March 2006, "Telephone evesdropper". You should be able to obtain
a copy via their website:
www.elektor-electronics.co.uk