Getting matching transformer from telephone

Ross Herbert wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
:Ross Herbert wrote:
:
:> Since your PC is mains powered and it may not have the required isolation
:> between the mains side and the sound card input you can do your own thing
:> using an approved 600:600 transformer with 3kV isolation rating to interface
the
:> telephone line to the sound card input.
:
:He DOES NOT need a 600 ohm transformer since the input impedance of the sound
:card is not 600 ohms <sigh> !

Since the application is merely detecting signal "voltage" it hardly matters
that the secondary impedance of the transformer is 600 ohms and the input
impedance of the sound card is more like 10Kohms. The only reason one tries to
match impedances is where one needs to maximise "power transfer" and that
doesn't apply in this case.
Click to expand...
Untrue. A non-optimally loaded audio transformer will not have a flat frequency
response. Nor is it about power transfer.

Graham
 
"Floyd L. Davidson" wrote:

"Phil Allison" <philallison@tpg.com.au> wrote:

Eg, a 600:600 ohm type operating into 10 kohms may well have a large
response peak at high frequencies while a 10k:10k type operating into 600
ohms will likely have serious roll off from a few kHz upwards.

So read what you just wrote, and tell us how that affects a telecom
circuit that is specified at 400-2800 kHz?

With transformers that have 1:10 or 1:20 step-up ratios for mic-input to a
valve stage, both load and source impedances become quite critical just to
stay within a +/- 2dB corridor across the audio band.

At perhaps 15-20 kHz. So just who cares, in this case?
Click to expand...
So, your argument is "Let's do it wrong because it really doesn't matter".
Pathetic.

Graham
 
In article <Xns9B8A6F7646E8374C1H4@69.16.176.253>, Paul B
<mail@nomail.invalid> scribeth thus
On Mon 05 Jan 02:26, Phil Allison <philallison@tpg.com.au> wrote


"Paul Bullshit ARTIST "


I take your (and other posters') points about a phone probably
not having a suitable transformer. My headache from trying to
make sense of some of the more technical aspects in this thread
suggests it might be easier in the end to go and buy some
600:600 transformers.


** Hey pal.

YOU already know what to do ( ie use a proper 600:600 ohms
ISOLATION transformer or a device incorporating same) ) and are
just objecting to a price of a few pounds.

Make you a fucking PITA wanker.

FUCK OFF.


I'm not too clear about this "CMRR" you mention.


** Who cares ?

YOU already know what to do ( ie use a proper 600:600 ohms
ISOLATION transformer or a device incorporating same) ) and are
just objecting to a price of a few pounds.

Make you a fucking PITA wanker.

FUCK OFF.


Any views and useful info from anyone would be most welcome.


** I bet this fuckhead is up to something that is highly
illegal !!!!

Hello Phil, I'm not sure what's triggered your response.

Is it really you replying or is it someone pretending? The headers
look real but I'm no expert in detecting an impersonation.

If it is you, then could you perhaps be upset that this thread has
shown so many technical trade-offs I never imagined (frequency
responses, impedances, matching, CMRR, etc) that I have looked more
widely and see digital solutions which might not have so much
subjective judgement? Or are you upset that other technical posters
have taken issue with some of your statments and you find the
discussion with them to be unwelcome? Please don't blame me for
that.

However, your post might be a clever spoof because you made the point
about how important "CMRR" is and when I looked it up but couldn't
understand it, the reply was "who cares". I also note the allegation
that I am may be undertaking illegal and I am sure the real poster
would not have arrived at such a conclusion from me asking how to
connect my home landline to my PC and then considering flash
recorders.

Who knows who you are. You seem to want to upset me.
Click to expand...

No its just him off his meds as usual. He's in uk.rec.audio where the
same hatred of us..........


*********************** !!!fecking pommie arseholes!!!...........

...can be found and every other vile*********

***************pommy or American- shithed- arsehole- who steals the eats
the earths Oxygen to breathe!..etc....


*********and they all are know nothing shitheads arseholes --insert
expletive of your choice--;!

So no your not any different at all!...

fortunately there aren't -that- many about like him thankfully;)...
--
Tony Sayer
 
"Paul Bullshit ARTIST "


** Hey pal.

YOU already know what to do ( ie use a proper 600:600 ohms
ISOLATION transformer or a device incorporating same) ) and are
just objecting to a price of a few pounds.

Make you a fucking PITA wanker.

So FUCK OFF !!




....... Phil
 
"Floyd L. Davidson" wrote:
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:
"Floyd L. Davidson" wrote:
Your point being? (Other than chest pounding?)

The point is that no one in their right mind expect a phone line to
be THAT quiet. OTOH, you might. I recall you bragging about recording
lots of phone calls in a C.O. at one time. What did that have to do with
PSTN?

1) I've never recorded a telephone call.
2) I've never worked in a C.O.
3) I know exactly how quiet a telephone line might be.

You are not discussing bridging though (or even VF
circuits), so I still don't see any point in all of that
nonsense.

Of course you don't. The circuits performed the same function, but
at a higher level of performance.

Except that isn't the case.

Something well beyond what was used in
telco. Telco doesn't use redundant systems and combine the outputs to
improve reliability.

Are you sure? (Remember all those whooshing noises on circuits that
went through White Alice? That was a combiner, mixing baseband signals
from redundant systems.)
Click to expand...

I never heard any noise like that on Alice. In fact, it was the
cleanest long distance calls I ever made, till fiber optics entered the
picture. Local calls that required the operator to find a number went
to Fairbanks. The road to was over 100 miles, so it would be something
near that for the alice microwave trunk. It was quiet. A hell of a lot
quieter than the lead cable inter CO trunk lines i used right after I
got out of the service. A call to another city that was less than ten
miles away was so bad you had to scream to be heard. Some of that went
away when Middletown got an early ESS to replace the '20s mechanical
scrap heap they had been repairing with parts from scrapped C.Os.


Tell me, Floyd. Could you balance those White Alice systems to .01
dB and keep them that way?



--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


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.
 
On Sun, 04 Jan 2009 20:36:09 -0900, floyd@apaflo.com (Floyd L. Davidson) wrote:

:Ross Herbert <rherber1@bigpond.net.au> wrote:
:
:> voice frequency circuits were all 300 - 3400Hz in my day.
:
:The PSTN is specified from 400 to 2800 Hz, with 24 dB SNR.
:
:Individual channels on various carrier systems, and some
:private line voice circuits are specified with more
:bandwidth.
:

In Australia PSTN is specified for 300 - 3400 Hz bandwidth.
 
On Mon, 05 Jan 2009 18:25:18 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

:
:
:Ross Herbert wrote:
:
:> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
:> :Ross Herbert wrote:
:> :
:> :> Since your PC is mains powered and it may not have the required isolation
:> :> between the mains side and the sound card input you can do your own thing
:> :> using an approved 600:600 transformer with 3kV isolation rating to
interface
:> the
:> :> telephone line to the sound card input.
:> :
:> :He DOES NOT need a 600 ohm transformer since the input impedance of the
sound
:> :card is not 600 ohms <sigh> !
:>
:> Since the application is merely detecting signal "voltage" it hardly matters
:> that the secondary impedance of the transformer is 600 ohms and the input
:> impedance of the sound card is more like 10Kohms. The only reason one tries
to
:> match impedances is where one needs to maximise "power transfer" and that
:> doesn't apply in this case.
:
:Untrue. A non-optimally loaded audio transformer will not have a flat frequency
:response. Nor is it about power transfer.
:
:Graham

With regard to a POTS line the VF bandwidth is some 300 - 3400Hz - hardly hi-fi
- so optimal flat frequency response is not an issue.

The fact that the secondary impedance of the 600 ohm transformer does not match
the input impedance of the sound card is totally unimportant in this
application.
 
In article <go36m45chgcb7sh1314n1povuc5754ala7@4ax.com>, rherber1
@bigpond.net.au says...>
On Sun, 04 Jan 2009 20:36:09 -0900, floyd@apaflo.com (Floyd L. Davidson) wrote:

:Ross Herbert <rherber1@bigpond.net.au> wrote:
:
:> voice frequency circuits were all 300 - 3400Hz in my day.
:
:The PSTN is specified from 400 to 2800 Hz, with 24 dB SNR.
:
:Individual channels on various carrier systems, and some
:private line voice circuits are specified with more
:bandwidth.
:

In Australia PSTN is specified for 300 - 3400 Hz bandwidth.
Click to expand...
How well do V.92 modems work or is the bandwidth really 4K (8K line
cards, and such)?
 
Ross Herbert wrote:
On Sun, 04 Jan 2009 20:36:09 -0900, floyd@apaflo.com (Floyd L. Davidson) wrote:

:Ross Herbert <rherber1@bigpond.net.au> wrote:
:
:> voice frequency circuits were all 300 - 3400Hz in my day.
:
:The PSTN is specified from 400 to 2800 Hz, with 24 dB SNR.
:
:Individual channels on various carrier systems, and some
:private line voice circuits are specified with more
:bandwidth.
:

In Australia PSTN is specified for 300 - 3400 Hz bandwidth.
Click to expand...
Also in the UK. Floyd seems to be referring to the US Bell standards.
The CCITT standards (which apply in most other parts of the world) are
different.

John
 
Ross Herbert <rherber1@bigpond.net.au> wrote:
On Sun, 04 Jan 2009 20:36:09 -0900, floyd@apaflo.com (Floyd L. Davidson) wrote:

:Ross Herbert <rherber1@bigpond.net.au> wrote:
:
:> voice frequency circuits were all 300 - 3400Hz in my day.
:
:The PSTN is specified from 400 to 2800 Hz, with 24 dB SNR.
:
:Individual channels on various carrier systems, and some
:private line voice circuits are specified with more
:bandwidth.
:

In Australia PSTN is specified for 300 - 3400 Hz bandwidth.
Click to expand...
I doubt it.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
 
John Livingston <null@spambin.com> wrote:
Ross Herbert wrote:
On Sun, 04 Jan 2009 20:36:09 -0900, floyd@apaflo.com (Floyd L. Davidson) wrote:
:Ross Herbert <rherber1@bigpond.net.au> wrote:
:
:> voice frequency circuits were all 300 - 3400Hz in my day.
:
:The PSTN is specified from 400 to 2800 Hz, with 24 dB SNR.
:
:Individual channels on various carrier systems, and some
:private line voice circuits are specified with more
:bandwidth.
:
In Australia PSTN is specified for 300 - 3400 Hz
bandwidth.

Also in the UK. Floyd seems to be referring to the US Bell standards.
The CCITT standards (which apply in most other parts of the world) are
different.
Click to expand...
You mean ITU-T standards, which is what both the UK and
Australia use. (It hasn't been CCITT for a long time.)

You are citing the bandwidth for an individual *channel*.
It is not possible to provide that sort of bandwidth on
every local loop, and therefore significantly less is
required for a complete connection or for any individual
loop.

Worse than that, the specification literally says
something to the effect of "if possible", and does not
prevent a telco from providing a loop that does not meet
the minimum specification.

Moreover, the 400-2800 Hz is not what you'd expect. It
is actually specified as up to 3 dB of rolloff per local
loop on any given connection. Plus up to 8 dB of
rolloff in the network switching fabric. Added up, that
means that both at 400 Hz and at 2800 Hz it would be
within specifications to have a connection that has 14
dB of rolloff compared to 1008 Hz.

Indeed, you will find that all of the ITU modem
standards (v.32, v.34, etc.) specify performance for a
400-2800 Hz connection as the minimal "voice grade"
specification.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
 
Floyd L. Davidson wrote:
You mean ITU-T standards, which is what both the UK and
Australia use. (It hasn't been CCITT for a long time.)

You are citing the bandwidth for an individual *channel*.
It is not possible to provide that sort of bandwidth on
every local loop, and therefore significantly less is
required for a complete connection or for any individual
loop.
Click to expand...
Are we discussing the same thing, I wonder ? The "Local Loop" is the
exchange - subscriber path, and is not bandwidth limited other than by
the basic line parameters. Hence the reason a local loop can (typically)
support 8Mbit ADSL.

Moreover, the 400-2800 Hz is not what you'd expect. It
is actually specified as up to 3 dB of rolloff per local
loop on any given connection. Plus up to 8 dB of
rolloff in the network switching fabric. Added up, that
means that both at 400 Hz and at 2800 Hz it would be
within specifications to have a connection that has 14
dB of rolloff compared to 1008 Hz.
Click to expand...
Which standard do you quote from ?
Could you cut and paste some text from this standard in support of this
statement ?

Indeed, you will find that all of the ITU modem
standards (v.32, v.34, etc.) specify performance for a
400-2800 Hz connection as the minimal "voice grade"
specification.

This may well be the case as the designers will work to the worst
Click to expand...
(international) case.

John
 
John Livingston wrote:

Floyd L. Davidson wrote:

You mean ITU-T standards, which is what both the UK and
Australia use. (It hasn't been CCITT for a long time.)

You are citing the bandwidth for an individual *channel*.
It is not possible to provide that sort of bandwidth on
every local loop, and therefore significantly less is
required for a complete connection or for any individual
loop.

Are we discussing the same thing, I wonder ? The "Local Loop" is the
exchange - subscriber path, and is not bandwidth limited other than by
the basic line parameters. Hence the reason a local loop can (typically)
support 8Mbit ADSL.
Click to expand...
Or up to 24 Mbps ADSL2+ !

Graham
 
"Floyd L. Davidson" wrote:

Ross Herbert <rherber1@bigpond.net.au> wrote:
floyd@apaflo.com (Floyd L. Davidson) wrote:
:Ross Herbert <rherber1@bigpond.net.au> wrote:
:
:> voice frequency circuits were all 300 - 3400Hz in my day.
:
:The PSTN is specified from 400 to 2800 Hz, with 24 dB SNR.
:
:Individual channels on various carrier systems, and some
:private line voice circuits are specified with more
:bandwidth.

In Australia PSTN is specified for 300 - 3400 Hz bandwidth.

I doubt it.
Click to expand...
You're just plain wrong about everything.

"Most of the current telephone systems are still restricted to the historically
motivated limitation of the bandwidth from 0.3 to 3.4 kHz."
http://portal.acm.org/citation.cfm?id=1142855&dl=&coll=

http://advancingphysics.iop.org/previous/wb/teacher/BandwidthW6.pdf

Graham
 
Ross Herbert wrote:

Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
:Ross Herbert wrote:
:> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
:> :Ross Herbert wrote:
:> :
:> :> Since your PC is mains powered and it may not have the required isolation
:> :> between the mains side and the sound card input you can do your own thing
:> :> using an approved 600:600 transformer with 3kV isolation rating to
interface the telephone line to the sound card input.
:> :
:> :He DOES NOT need a 600 ohm transformer since the input impedance of the
sound card is not 600 ohms <sigh> !
:
:> Since the application is merely detecting signal "voltage" it hardly matters
:> that the secondary impedance of the transformer is 600 ohms and the input
:> impedance of the sound card is more like 10Kohms. The only reason one tries
to match impedances is where one needs to maximise "power transfer" and that
:> doesn't apply in this case.
:
:Untrue. A non-optimally loaded audio transformer will not have a flat frequency
:response. Nor is it about power transfer.
:
:Graham

With regard to a POTS line the VF bandwidth is some 300 - 3400Hz - hardly hi-fi
- so optimal flat frequency response is not an issue.

The fact that the secondary impedance of the 600 ohm transformer does not match
the input impedance of the sound card is totally unimportant in this
application.
Click to expand...
So your attitude is "it's so bad it doesn't matter messing it up even more".

A proper 600:600 transformer will be more expensive than a 10k:10k one too.

Graham
 
John Livingston <null@spambin.com> wrote:
Floyd L. Davidson wrote:
You mean ITU-T standards, which is what both the UK and
Australia use. (It hasn't been CCITT for a long time.)
You are citing the bandwidth for an individual
*channel*.
It is not possible to provide that sort of bandwidth on
every local loop, and therefore significantly less is
required for a complete connection or for any individual
loop.

Are we discussing the same thing, I wonder ? The "Local Loop" is the
exchange - subscriber path, and is not bandwidth limited other than by
the basic line parameters. Hence the reason a local loop can (typically)
support 8Mbit ADSL.
Click to expand...
But typically supporting 8 Mb has nothing to do with the
minimum bandwidth specification. The *fact* is that telcos
can and do provide POTS service over local loops that have no
more than 400-2800 Hz bandwidth.

Moreover, the 400-2800 Hz is not what you'd expect. It
is actually specified as up to 3 dB of rolloff per local
loop on any given connection. Plus up to 8 dB of
rolloff in the network switching fabric. Added up, that
means that both at 400 Hz and at 2800 Hz it would be
within specifications to have a connection that has 14
dB of rolloff compared to 1008 Hz.

Which standard do you quote from ?
Could you cut and paste some text from this standard in support of this
statement ?
Click to expand...
Look it up yourself. If you want to claim it is
something else, you are welcome to provide a cite
yourself.

Indeed, you will find that all of the ITU modem
standards (v.32, v.34, etc.) specify performance for a
400-2800 Hz connection as the minimal "voice grade"
specification.

This may well be the case as the designers will work to the worst
(international) case.
Click to expand...
It is not the designer's option, it is the ITU standards
that require it.

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

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

By WHOM ?
Click to expand...
ITU-T standards and Bellcore standards.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
 
Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:
John Livingston wrote:

Floyd L. Davidson wrote:

You mean ITU-T standards, which is what both the UK and
Australia use. (It hasn't been CCITT for a long time.)

You are citing the bandwidth for an individual *channel*.
It is not possible to provide that sort of bandwidth on
every local loop, and therefore significantly less is
required for a complete connection or for any individual
loop.

Are we discussing the same thing, I wonder ? The "Local Loop" is the
exchange - subscriber path, and is not bandwidth limited other than by
the basic line parameters. Hence the reason a local loop can (typically)
support 8Mbit ADSL.

Or up to 24 Mbps ADSL2+ !
Click to expand...
And *down* to 400-2800 Hz.

--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top