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Getting matching transformer from telephone

R

Ross Herbert

Jan 1, 1970
0
On Sat, 03 Jan 2009 22:51:18 -0900, [email protected] (Floyd L. Davidson) wrote:

:>"Ross Herbert"
:>
:>>
:>> 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.
:>
:>** Fact is, it will be an advantage as the load across the phone line
:>needs to be high as possible so the level there is not affected.
:
:No, it merely needs to be "high enough", not "high as
:possible". If the bridging device has ten times the
:circuit impedance, there will be a 0.3 dB drop in levels
:eek:n the circuit, and a 30 dB loss across the bridging
:device.
:
:That is considered satisfactory for virually all
:applications. In this instance it would probably be
:satisfactory if the bridging impedance where half that.
:
:Regardless, you 10k Ohm value is absurd.
:
:>> The only reason one tries to
:>> match impedances is where one needs to maximise "power transfer" and that
:>> doesn't apply in this case.
:>
:>** Nonsense.
:>
:>Audio and other wide band transformers have rated ( ie optimum) source and
:>load impedances.
:>
:>This relates *directly* to them both operating efficiently AND exhibiting
:>their specified frequency response curve.
:>
:>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?

Should that not be Hz?

If so, voice frequency circuits were all 300 - 3400Hz in my day.

Phil is just being a bit too specific. My remarks were applicable specifically
to the VF telephony freq range, which is the area of interest to the OP.

:
:>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?

Exactly!
 
P

Phil Allison

Jan 1, 1970
0
"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.

**** 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.

**** OFF.

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


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

Secretly recording a phone conversations that YOU are NOT one party to is
a crime in most places - including the UK.

Plus, even then, the recording MUST NOT BE used for ANY purpose other
than protecting your own legitimate interests.



...... Phil
 
P

Paul B

Jan 1, 1970
0
On Mon 05 Jan 02:26 said:
"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.

**** OFF.




** 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.

**** OFF.




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

Secretly recording a phone conversations that YOU are NOT one
party to is a crime in most places - including the UK.

Plus, even then, the recording MUST NOT BE used for ANY
purpose other than protecting your own legitimate interests.

..... Phil


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.
 
P

Paul B

Jan 1, 1970
0
On Mon 29 Dec 15:36, Eeyore
Cheaper to buy a decent sound card with balanced ins and outs
(plus not on those GHASTLY 3.5mm jacks) and learn how to use
them properly.

Terratec do a moderately inexpensive one IIRC.

Graham

Graham, I must say a better sound card is attractive. I checked out
Terratec which you mentioned. Their web site lists the Aureon 5.1 PCI
card but it has those potentially noisy 3.5 mm jack sockets.

http://www.terratec.net/en/products/Aureon_5.1_PCI_1988.html

I assume the noise would be from the build quality of the 3.5 mm jack
plug as it seems to usually have a rivetted centre core that could
and turn. The contacts in the sockets are also probably very basic.

To see what I would need to do for the balanced cicruit you were
recommending I Googled Epanorama and saw this:
<http://www.epanorama.net/circuits/teleinterface.html>
In the section called "Interference in the telephone line signal" it
refers to a heavy 1 kg choke or transformer! That seems a bit of a
non-starter.

I also saw the "DMX 6Fire USB" at Terratec but it seems too spartan
and is not cheap at over £150.
http://www.terratec.net/en/products/DMX_6Fire_USB_2084.html

So I have also checked out a few alternatives to the Terratec and I
mention them at the end of my post to Phil Allison. They are:

(a) a Behringer Xenyx 502 mixer (£32)
<http://www.dv247.com/invt/31558/>

(b) an analogue to digital interface Behringer UCA202 for £20
<http://www.dv247.com/invt/32730/>

(C) or something which combines the two.

My post about this is at:

Google Groups: http://preview.tinyurl.com/ay6hew

-------=======------

Phew! That's a lot of researching!

Is there a simple circuit you know to attach the phone to the PC in a
a balanced way?

Any constructive comments would be welcome.

Thank you.

PB
 
E

Eeyore

Jan 1, 1970
0
Ross said:
: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
 
E

Eeyore

Jan 1, 1970
0
Floyd L. Davidson said:
So read what you just wrote, and tell us how that affects a telecom
circuit that is specified at 400-2800 kHz?


At perhaps 15-20 kHz. So just who cares, in this case?

So, your argument is "Let's do it wrong because it really doesn't matter".
Pathetic.

Graham
 
T

tony sayer

Jan 1, 1970
0
Paul B said:
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.


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;)...
 
R

Ross Herbert

Jan 1, 1970
0
On Sun, 04 Jan 2009 20:36:09 -0900, [email protected] (Floyd L. Davidson) 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.
 
R

Ross Herbert

Jan 1, 1970
0
On Mon, 05 Jan 2009 18:25:18 +0000, Eeyore

:
:
:Ross Herbert 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.
 
K

krw

Jan 1, 1970
0
rherber1 said:
On Sun, 04 Jan 2009 20:36:09 -0900, [email protected] (Floyd L. Davidson) 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.

How well do V.92 modems work or is the bandwidth really 4K (8K line
cards, and such)?
 
J

John Livingston

Jan 1, 1970
0
Ross said:
On Sun, 04 Jan 2009 20:36:09 -0900, [email protected] (Floyd L. Davidson) 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.

John
 
J

John Livingston

Jan 1, 1970
0
Floyd said:
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.
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 ?
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.

John
 
E

Eeyore

Jan 1, 1970
0
John said:
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+ !

Graham
 
E

Eeyore

Jan 1, 1970
0
Ross said:
:Ross Herbert 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.

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
 
P

PCPaul

Jan 1, 1970
0
'Friendly fire' accidents do happen. Mostly due to the troops of
various countries not following the instructions for proper ID, correct
passwords, or keeping up with the proper communications for the day or
mission. Some are simply where they were told not to be. Either they
ignored the orders, or the command chain was so slow it never arrived.

They do. But they happen far more in some countries armies than others.

Would you rather they be captured and tortured to death by the enemy?

As opposed to being wounded or killed by their 'friends'? No.
 
P

PCPaul

Jan 1, 1970
0
They do. But they happen far more in some countries armies than others.



As opposed to being wounded or killed by their 'friends'? No.

Or rather yes. Damn.


I guess I'll have to stop Yank baiting now.

However - having worked for the MOD as a civvie for many years, I know
loads of UK service personnel. And they are unanimously nervous of being
posted to places where they have to fight alongside US forces. That ain't
right.
 
P

PCPaul

Jan 1, 1970
0
Then they should be better trained to work with other troops.

Training to hide from them, you mean?

'Working with other troops' doesn't mean 'shoot first, ask questions
later'. Maybe it's a language thing.

I *know* that US simulator training has had to have massive amounts of
work done in the last few years to add 'friendlies' into the equation.
even then there was a lot of resistance to having hitting one of these
friendlies actually damage the health or 'score' of the shooter.. it
spoiled the fun of blasting everything that moved.

Anyway, if the combined non-US coalition forces couldn't get through to
the US hierarchy, then me moaning at you on here isn't going to do
anything, so I'm off now. Bye.
 
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