Getting matching transformer from telephone

[SoothSayer]

On Sun, 04 Jan 2009 18:42:50 +0000, John Livingston <null@spambin.com>
wrote:

Stuart wrote:
In article <87r63pi7wq.fld@apaflo.com>,
Floyd L. Davidson <floyd@apaflo.com> wrote:
Yes, we did send program feeds from London to Burghead in Scotland
via landline.
Correct. I've worked on circuit equalisation at Burghead end. It was
baseband audio - not carrier.

And you have no idea what was in between.

You sent them that distance via FDM carrier systems, not
via landlines, even in the 1930's.
Very rarely - most carrier channels were 300-3400Hz.

Yes, most were. But not all. It was relatively easy to
use a double wide channel, or use a groupband device
that took up 48 KHz.

The noise and
distortion figures came nowhere near the requirements for broadcast
audio.

So you think an equalized audio channel over cable
would, after 600 miles????

I now have some more information on this.

To quote:

"Studio Engineering for Sound Broadcasting" Illife 1955.
Chapter 7 "Programme circuits on Post Office Lines" G Stannard, Bsc
A.M.I.E.E - Lines department.

p142. "The distribution of BBC Light Programme to Burghead at the time of
writing contains 693 miles of 16mH/1.136m. and the estimated delay
distortion relative to 1kc/s is:
50 c/s 50m.sec
100 c/s 9.5m.sec
7 kc/s 7.3 m.sec"

16mH/1.136m describes a loaded line and m, in this case, would be miles.
Elsewhere a table gives the following information for this type of line:

Weight of conductor 40lb/mile, Approx characteristic impedance 490 ohms,
Cut-off frequency 9.3kc/s, maximum useable frequency 7.44kc/s.

The book further goes on to discuss carrier circuits

p131 (Same chapter)

"In 1938 the Post Office began a big expansion in their communication
network by laying 12-channel carrier cables. These are low capacitance
cables specifically designed for the transmission of frequencies up to 60
kc/s and subsequently up to 120kc/s"

Two schemes are discussed for using carrier circuit lines but they are
described (p155) as inferior to circuits obtained by more conventional
methods.


Thanks Stuart - this fits exactly with my memories of the time. It was a
while back though ......
The BBC now has its own digital audio distribution systems, and no
longer requires the widespread use of BT programme circuits.

To reiterate for those who have generated all the heat and the
fabulously inaccurate rantings - The programme circuits were BASEBAND
AUDIO all the way - amplified en route. As Stuart quotes - carrier is
possible, but provides worse noise and distortion standards.

Carrier was not generally used for main UK programme distribution (sorry
Floyd - you may be right about American practice, but not UK).

John

Now that was the right, properly worded response to Floyd. Good job.

I wonder where this places the retarded donkey's assertions, if he ever
actually made any, other than his rantings. He did claim to have a
fairly deep knowledge... that he had a schematic.... somewhere.

It would be nice to see your document posted up in
alt.binaries.schematics.electronic, if, that is, you have access to it.

 

[Stuart]

In article <pu12m45jj4hjudigir9vv4ih8agva479sk@4ax.com>,
SoothSayer <SaySooth@TheMonastery.org> wrote:

It would be nice to see your document posted up in
alt.binaries.schematics.electronic, if, that is, you have access to it.

It's a 200 page book and I'm afraid I don't really have the time.
Copyright might also be an issue. One or two pages I suppose I could
manage but which ones?

My current project is going through hundreds of old electronics magazines
and scanning to PDF, stuff that I find of interest.

--
Stuart Winsor

For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk

 

[ItsASecretDummy]

On Sun, 04 Jan 2009 20:54:04 +0000 (GMT), Russell Hafter News
<see.sig@walkingingermany.invalid> wrote:

I do the exact opposite - if I get an *interesting* PDF,
then I print it and store the hard copy.

Fucking environmental retard! Do you do the stupid twit act of
printing out your e-mails as well, you stupid fuck?

 

[ItsASecretDummy]

On Sun, 04 Jan 2009 20:54:04 +0000 (GMT), Russell Hafter News
<see.sig@walkingingermany.invalid> wrote:

I just cannot cope with trying to read complex documents on
a screen, and the pink highlighter on the screen does not
scroll with the page, either
)

Indicative of piss poor grasp of modern computer technology, not to
mention quite lame document handling capacity. You don't know how to add
a highlight to a doc on screen? Perhaps you need a mini NASCAR scrolling
bug screen you can scroll with your document, dipshit?

Bwuahahahahahah!

 

[Russell Hafter News]

In article <501887a418Spambin@argonet.co.uk>, Stuart
<Spambin@argonet.co.uk> wrote:

In article <pu12m45jj4hjudigir9vv4ih8agva479sk@4ax.com>,
SoothSayer <SaySooth@TheMonastery.org> wrote:

It would be nice to see your document posted up in
alt.binaries.schematics.electronic, if, that is, you
have access to it.

It's a 200 page book and I'm afraid I don't really have
the time. Copyright might also be an issue. One or two
pages I suppose I could manage but which ones?

My current project is going through hundreds of old
electronics magazines and scanning to PDF, stuff that I
find of interest.

Gosh, Stuart, why??

I do the exact opposite - if I get an *interesting* PDF,
then I print it and store the hard copy.

I just cannot cope with trying to read complex documents on
a screen, and the pink highlighter on the screen does not
scroll with the page, either
)

--
Russell
http://www.russell-hafter-holidays.co.uk
Russell Hafter Holidays E-mail to enquiries at our domain
Need a hotel? <http://www.hrs.de/?client=en__MT&customerId=416873103>

 

[Salmon Egg]

In article <bh92m4hu1cjrgsf67d21pc8g7gv30tep9f@4ax.com>,
ItsASecretDummy <secretasianman@thebarattheendoftheuniverse.org>
wrote:

On Sun, 04 Jan 2009 20:54:04 +0000 (GMT), Russell Hafter News
see.sig@walkingingermany.invalid> wrote:

I just cannot cope with trying to read complex documents on
a screen, and the pink highlighter on the screen does not
scroll with the page, either
)

Indicative of piss poor grasp of modern computer technology, not to
mention quite lame document handling capacity. You don't know how to add
a highlight to a doc on screen? Perhaps you need a mini NASCAR scrolling
bug screen you can scroll with your document, dipshit?

Bwuahahahahahah!

It is difficult to writer complex documents for publication. Most, but
not all, postings are not written well. I am guilty of contributing a
few myself. It is not the medium; it is the writer.

Bill

--
Private Profit; Public Poop! Avoid collateral windfall!

 

[Stuart]

In article <50188aa948see.sig@walkingingermany.invalid>,
Russell Hafter News <see.sig@walkingingermany.invalid> wrote:

Hi Russell,

Gosh, Stuart, why??

Space.

I need to make more space for books and new magazines so I need to get rid
of some old magazines. I'm currently going through my copies of Elektor
which date back to UK issue 1. I don't have them all mind you, there was a
sizable period when I didn't subscribe, before I took out a new
subscription to see what it was like, and I'm not currently a subscriber -
it's too obsessed with micro-controllers.

So far I've gone through about 100 magazines and used up just over 40M of
hard drive space.

I do the exact opposite - if I get an *interesting* PDF,
then I print it and store the hard copy.

There was a time when I used to photocopy something that really caught my
eye and I'd store in files by content (especially if it was a magazine I
didn't own!) but that is also too wasteful of space - not to say paper.

--
Stuart Winsor

For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk

 

[Paul B]

On Sat 03 Jan 01:27, Phil Allison <philallison@tpg.com.au> wrote

Stuart:


However, regardless of what you know or don't know, this thread
was started by someone who wanted to know whether he could
re-use the transformers in telephones for another purpose so
clearly he has some!


** That is entirely false.

What the OP *actually asked* was this:

" If I strip down some landline phones I 've got here, then
will there be a matching transformer in each one? "

Chances are high there are no iron core transformers ( hybrid or
other) in his phones at all - cos they are too modern.

Secondly, his purpose requires a transformer with high voltage
safety isolation from the phone line - which the common
600:600 ohms phone line types all have and others do not.

Thirdly, his purpose requires a transformer with very high CMRR
- cos that is why he is getting humming noises at the moment
when making recordings with his passive ( ie non-transformer )
adaptor device.

Have you ever done this ??

I can assure you it ain't as simple as you suspect to get a hum
free and distortion free result.

Not the least of the problems is that portable voice recorders
have high sensitivity mic inputs with automatic gain control
circuits - which cannot be defeated by the user. This results
in annoying gain pumping and regular bursts of overload
distortion PLUS increasing background noise & hum whenever
there is a pause in the conversation.

The trick is to use just the right amount of resistive divider
attenuation before and after the 1:1 transformer to eliminate
this - plus cap couple the input side to stop pulling the
line low.

..... Phil

Hi Phil and others. I am the original poster. Thank you to everyone
who has kindly contributed to this discussion.

Please don't overlook some details I posted at:
news:Xns9B8756CEC79974C1H4@69.16.176.253
http://groups.google.com/group/uk.telecom/msg/4513d4edcdc47c3e

You are quite right about high sensitivity mic inputs and automatic
gain controls. As you can imagine, when the phone's handset is
picked up and used, the mic input is faced with something approaching
line levels and I get severe overload of my recorder. Then when it
goes quiet, the AGC kicks in. It's as you describe.

I have tried to "listen through" any such automatic gain as best as I
could and I feel there is still detect much more hum than I would
expect on the line.

In truth, I really need a more suitable flash recorder but they are
harder to find than I expected.

Currently I use the Olympus WS-331M.
<http://www.olympus.co.uk/consumer/2581_WS-331M.htm>

Cost is important to me so I don't want to fork out for a digital
field recorder like this low-end one especially as some reviews have
not been kind to it. <http://www.dv247.com/invt/41901/>.

Prices in the flash-memory recorder market are tumbling such that now
personal video recorders (like the Archos AV400) are about the same
price and offer some additional very useful function. Although i
don't know if that sort of model has suitable input and output
sockets.

On the other hand, I don't want some MP3 player with a recorder
thrown in as an afterthought because ones I have seen can have
surprisingly limited bit rates and low quality. Anyway, many
probably don't have a line level input, so I will once again most
likely get problems with a mic input and AGC.

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.

I'm not too clear about this "CMRR" you mention. I know next to
nothing about "common mode rejection ratio" although I did come
across the concept when looking at balanced inputs with chunky XLR
connectors. I googled it and got the following PDF but in the end I
couldn't really understand anything in it about CMRR. Do I really
need to consider CMRR if I am going to be making a recording from a
phone line?

<http://www.jensentransformers.com/an/Audio%20Transformers%
20Chapter.pdf>

One new line of thinking I would like to bounce off you and the other
kind contributors to this thread is whether it is possible in my case
to use a simple mixer (like those a pop group might use). If I can
avoid those 3-wire balanced inputs on such a mixer and use just the
2-wire inputs then would the mixer's op amps and other electronics
have a suitable isolating effect? The price of such a mixer seems
very competitive. I am thinking of a unit similar to this one:

Behringer XENYX 502 (Ł32) http://www.dv247.com/invt/31558/

In turn, that leads me to consider if I should attempt to get a
separate a analogue-to-digital converter which goes into the PC via
the USB. That way I hope to eliminate earth loop hum and other
spurious noises which I mentioned in my first post.

Maybe something like the Behringer UCA202 for Ł20
http://www.dv247.com/invt/32730/? To be honest I have no idea if
this would work but it seems to be good value.

I'm sorry to be darting about with various options but I didn't know
it was going to be so complicated!

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

Andy.

 

[Ross Herbert]

On Sat, 03 Jan 2009 22:51:18 -0900, floyd@apaflo.com (Floyd L. Davidson) wrote:

:"Phil Allison" <philallison@tpg.com.au> 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
ossible". If the bridging device has ten times the
:circuit impedance, there will be a 0.3 dB drop in levels
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!

 

[Phil Allison]

"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 !!!!

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

 

[Floyd L. Davidson]

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:

"Floyd L. Davidson" wrote:
That would work, but a 600 ohm load would give the flattest frequency
response,

Not true. It won't necessarily change the frequency
response at all, much less significantly.

That depends on what you consider significant. Even though the telco
bandwidth is limited, there is little reason to make it worse.

No, I'm saying it will not *necessarily* change the
response. It depends on the transformer and other
circuit components. It *might* be a problem, but you
said it absolutely would.

and a -3 dB change would be equal to someone picking up an
extension. Some signal loss, but not outside the design limits.

Not necessarily! You have no way to know how close it
already is to design limits, and therefore you cannot
make the assumption that using up the entire "slack"
allowed for will not instead put it exactly that far out
of specs.

So you are saying that there are lines in use that can't have a
working extension in use with the main phone?

Yes. But worse yet, if they do and you put something
like that on the line, then they can't! If there were
no alternative, it would be acceptable and one would
just have to not use it if it caused a problem. But
since it is easy to design it to *never* cause level
problems, that is exactly the way it should be designed.

The sound card he intends
to use has far more than 3 dB gain for the line level inputs.

Which also amplifies noise too. Bad design...

I have seen network feeds via Telco plant that were so bad that they
hit the building at more than -20 dB.

Network feeds are an entirely different beast than
connecting to the PSTN.

At one they insisted it was
leaving their C.O. at 0 dB, but we had to turn everything wide open to
get even close to 100% modulation. I used a spare magnetic phono preamp
to bring it up closer to 0 dB, and had to put up with the RIAA
equalization for the network feed. When people complained, we told them
why the network sounded so bad. BTW, that feed was through White Alice.

You were lucky you could hear it!

Actually, if that was the AFRN feed, you should have
been able to cause all sorts of commotion! That was the
highest priority circuit in Alaska for the entire life
of the White Alice Comm System!

The
best choice would be a telephone interface like those used for radio
stations.

Assuming money is no object, nor is space.

I'm a former Radio & TV broadcast engineer. Both were
considerations, but performance and reliability were more important.
Dead air is very, very expensive. It can cost you advertisers as well
as listeners. Enough of it can cost you your license.

Pass out towels with your sob stories? (It doesn't have
anything to do with this tale of woe.)

They are bi-directional, and allow the host to talk to the
listeners, and the caller at the same time. They will work reliably,
even if there is a -20 dB change in line level.

And did you note the price tag on a good one? That is
necessarily a non-trivial design. (Try it sometime! They
are fun, especially if you want to be able to bridge
multiple lines.)

I have. The design isn't that difficult, but the market is tiny so
the engineering costs don't have millions of units to defray the costs.
Electron hybrids are a handful of op-amps and the concept has been
around for a long time. Try designing a high performance AGC system for
tracking satellites. The last one I worked with had 14 op-amps and less
than 1.5 mV error over a 0 to 5 volt range. This was used to combine
(similar to bridging) two unmatched video sources to a proper 0 dBm
output with less than a .01 dB tracking error. That is something you
would never try to do with a couple phone lines.

Oh, goodness, those towels had better be beach size.
This is a lot of tear jerking material. (But, alas,
other than that wonderful rhythm you make thumping on
your chest, it has nothing to do with this particular
thread.)

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

 

[Michael A. Terrell]

"Floyd L. Davidson" wrote:

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:
"Floyd L. Davidson" wrote:
That would work, but a 600 ohm load would give the flattest frequency
response,

Not true. It won't necessarily change the frequency
response at all, much less significantly.

That depends on what you consider significant. Even though the telco
bandwidth is limited, there is little reason to make it worse.

No, I'm saying it will not *necessarily* change the
response. It depends on the transformer and other
circuit components. It *might* be a problem, but you
said it absolutely would.

and a -3 dB change would be equal to someone picking up an
extension. Some signal loss, but not outside the design limits.

Not necessarily! You have no way to know how close it
already is to design limits, and therefore you cannot
make the assumption that using up the entire "slack"
allowed for will not instead put it exactly that far out
of specs.

So you are saying that there are lines in use that can't have a
working extension in use with the main phone?

Yes. But worse yet, if they do and you put something
like that on the line, then they can't! If there were
no alternative, it would be acceptable and one would
just have to not use it if it caused a problem. But
since it is easy to design it to *never* cause level
problems, that is exactly the way it should be designed.

It depends on the situation, how long you need it, and if it will be
used on a continuing basis. If the telco plant is that flaky, it needed
repaired.

I had to do a live remote at the Army base and they refused to set up
the copper pair for our feed in time so I took a spare audio board to
the site, and some alligator clips. I dialed the cleanest phone line to
the station and connected the transformer coupled line output to the
phone line, then hung up the phone. The transformer had no trouble with
the DC bias, and the feed worked. They threw a fit when they found out,
but the General was happy that the feed worked.

The sound card he intends
to use has far more than 3 dB gain for the line level inputs.

Which also amplifies noise too. Bad design...

Compared to the noise from a carbon microphone?

I have seen network feeds via Telco plant that were so bad that they
hit the building at more than -20 dB.

Network feeds are an entirely different beast than
connecting to the PSTN.

They are closer to what the OP wants to do.

At one they insisted it was
leaving their C.O. at 0 dB, but we had to turn everything wide open to
get even close to 100% modulation. I used a spare magnetic phono preamp
to bring it up closer to 0 dB, and had to put up with the RIAA
equalization for the network feed. When people complained, we told them
why the network sounded so bad. BTW, that feed was through White Alice.

You were lucky you could hear it!

Actually, if that was the AFRN feed, you should have
been able to cause all sorts of commotion! That was the
highest priority circuit in Alaska for the entire life
of the White Alice Comm System!

They only worried about it while it was 'on Alice'. When it went to
the old lead clad telco lines it was the military's problem, and they
local group didn't care. The only clean phone line to the broadcast
complex went to a boiler room at the far end. Maintenance used it when
they were there for repairs so it was rarely used. The station's lines
all had so much noise that it wasn't funny. Our complaints always got
the same response. "That trunk line is to be replaced in five years, so
you'll just have to live with it." Some had so much RF problems that
the AM radio signal was louder than either party.

The
best choice would be a telephone interface like those used for radio
stations.

Assuming money is no object, nor is space.

I'm a former Radio & TV broadcast engineer. Both were
considerations, but performance and reliability were more important.
Dead air is very, very expensive. It can cost you advertisers as well
as listeners. Enough of it can cost you your license.

Pass out towels with your sob stories? (It doesn't have
anything to do with this tale of woe.)

Only because you don't want to hear it. If the phone lines are down
for long, it cost the telco money, too.

They are bi-directional, and allow the host to talk to the
listeners, and the caller at the same time. They will work reliably,
even if there is a -20 dB change in line level.

And did you note the price tag on a good one? That is
necessarily a non-trivial design. (Try it sometime! They
are fun, especially if you want to be able to bridge
multiple lines.)

I have. The design isn't that difficult, but the market is tiny so
the engineering costs don't have millions of units to defray the costs.
Electron hybrids are a handful of op-amps and the concept has been
around for a long time. Try designing a high performance AGC system for
tracking satellites. The last one I worked with had 14 op-amps and less
than 1.5 mV error over a 0 to 5 volt range. This was used to combine
(similar to bridging) two unmatched video sources to a proper 0 dBm
output with less than a .01 dB tracking error. That is something you
would never try to do with a couple phone lines.

Oh, goodness, those towels had better be beach size.
This is a lot of tear jerking material. (But, alas,
other than that wonderful rhythm you make thumping on
your chest, it has nothing to do with this particular
thread.)

You brought up bridging so get your own towels. Interfaces are a
hell of a lot simpler than they were 50 years ago. For instance, Clare
has the whole interface on a single IC:
<http://www.clare.com/home/pdfs.nsf/www/AN-146.pdf/$file/AN-146.pdf>


--
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.

 

[Floyd L. Davidson]

Ross Herbert <rherber1@bigpond.net.au> wrote:

On Sat, 03 Jan 2009 22:51:18 -0900, floyd@apaflo.com (Floyd L. Davidson) 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?

Should that not be Hz?

Yes.

If so, 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.

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!

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

 

[Floyd L. Davidson]

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:

"Floyd L. Davidson" wrote:
and a -3 dB change would be equal to someone picking up an
extension. Some signal loss, but not outside the design limits.

Not necessarily! You have no way to know how close it
already is to design limits, and therefore you cannot
make the assumption that using up the entire "slack"
allowed for will not instead put it exactly that far out
of specs.

So you are saying that there are lines in use that can't have a
working extension in use with the main phone?

Yes. But worse yet, if they do and you put something
like that on the line, then they can't! If there were
no alternative, it would be acceptable and one would
just have to not use it if it caused a problem. But
since it is easy to design it to *never* cause level
problems, that is exactly the way it should be designed.

It depends on the situation, how long you need it, and if it will be
used on a continuing basis. If the telco plant is that flaky, it needed
repaired.

There is nothing there suggesting the telco plant is
flaky or needs repair. It just says they do have design
parameter targets, and that good design will adhere to
the specifications.

I had to do a live remote at the Army base and they refused to set up
the copper pair for our feed in time so I took a spare audio board to
the site, and some alligator clips. I dialed the cleanest phone line to
the station and connected the transformer coupled line output to the
phone line, then hung up the phone. The transformer had no trouble with
the DC bias, and the feed worked. They threw a fit when they found out,
but the General was happy that the feed worked.

Your point being? (Other than chest pounding?)

The sound card he intends
to use has far more than 3 dB gain for the line level inputs.

Which also amplifies noise too. Bad design...

Compared to the noise from a carbon microphone?

It amplifies that too.

Your point being? (Other than chest pounding?)

I have seen network feeds via Telco plant that were so bad that they
hit the building at more than -20 dB.

Network feeds are an entirely different beast than
connecting to the PSTN.

They are closer to what the OP wants to do.

The OP is talking about the PSTN, only.

At one they insisted it was
leaving their C.O. at 0 dB, but we had to turn everything wide open to
get even close to 100% modulation. I used a spare magnetic phono preamp
to bring it up closer to 0 dB, and had to put up with the RIAA
equalization for the network feed. When people complained, we told them
why the network sounded so bad. BTW, that feed was through White Alice.

You were lucky you could hear it!

Actually, if that was the AFRN feed, you should have
been able to cause all sorts of commotion! That was the
highest priority circuit in Alaska for the entire life
of the White Alice Comm System!

They only worried about it while it was 'on Alice'. When it went to
the old lead clad telco lines it was the military's problem, and they
local group didn't care. The only clean phone line to the broadcast
complex went to a boiler room at the far end. Maintenance used it when
they were there for repairs so it was rarely used. The station's lines
all had so much noise that it wasn't funny. Our complaints always got
the same response. "That trunk line is to be replaced in five years, so
you'll just have to live with it." Some had so much RF problems that
the AM radio signal was louder than either party.

So if the problem was the Army (you), why complain about WACS?

I'm a former Radio & TV broadcast engineer. Both were
considerations, but performance and reliability were more important.
Dead air is very, very expensive. It can cost you advertisers as well
as listeners. Enough of it can cost you your license.

Pass out towels with your sob stories? (It doesn't have
anything to do with this tale of woe.)

Only because you don't want to hear it. If the phone lines are down
for long, it cost the telco money, too.

Your point being? (Other than chest pounding?)

I have. The design isn't that difficult, but the market is tiny so
the engineering costs don't have millions of units to defray the costs.
Electron hybrids are a handful of op-amps and the concept has been
around for a long time. Try designing a high performance AGC system for
tracking satellites. The last one I worked with had 14 op-amps and less
than 1.5 mV error over a 0 to 5 volt range. This was used to combine
(similar to bridging) two unmatched video sources to a proper 0 dBm
output with less than a .01 dB tracking error. That is something you
would never try to do with a couple phone lines.

Oh, goodness, those towels had better be beach size.
This is a lot of tear jerking material. (But, alas,
other than that wonderful rhythm you make thumping on
your chest, it has nothing to do with this particular
thread.)

You brought up bridging so get your own towels.

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

Your point being? (Other than chest pounding?)

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

 

[Paul B]

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 !!!!

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.

 

[Paul B]

On Mon 29 Dec 15:36, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote

Stuart wrote:

Paul B <mail@nomail.invalid> wrote:

If I strip down some landline phones I 've got here, then
will there be a matching transformer in each one? Or is
their technology different now?

Even if there is (they used to use hybrids but I don't know
these days) the quality will be poor. They are only intended
for voice. For music you require a much larger bandwidth and
lower distortion characteristics. Expect to pay at least Ł30-50
for something decent by Sowter or similar. Ideally, you will
also need to know the impendence of your sound card input to
match it properly, or assume it is high (it probably is) and
resistively terminate the transformer secondary.

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 Ł150.
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 (Ł32)
<http://www.dv247.com/invt/31558/>

(b) an analogue to digital interface Behringer UCA202 for Ł20
<http://www.dv247.com/invt/32730/>

(C) or something which combines the two.

My post about this is at:

news:Xns9B8A15B4A335B74C1H4@216.151.153.41
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

 

[Stuart]

In article <Xns9B8A6F7646E8374C1H4@69.16.176.253>,
Paul B <mail@nomail.invalid> wrote:

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

I'm afraid there seem to be plenty of people around here who's sole
pleasure in life is to hurl abuse and insults at anyone and everyone.

Even the remotest thing they seem to take a dislike to, or disagree with,
for whatever reason, provokes a torrent of foul language with no reasoned
or sensible argument.

I'm afraid a very thick skin is needed round here.

I am quite sure you have good and honest reasons why you wish to record
telephone conversations. Some years ago when doing research into my family
history I conducted a number of "interviews" with my father over the phone
and these were recorded onto tape using the telephone answering machine,
which had a recording facility, that we had at the time.

A while ago when receiving abuse from one of these cold calling telephone
sales people, from ADT as it happens, I wished I had had telephone
recording that I could have passed on to the police.

The best advice I can give is to read and filter out the useful advice and
ignore everything else.

--
Stuart Winsor

For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk

 

[Michael A. Terrell]

"Floyd L. Davidson" wrote:

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote:

It depends on the situation, how long you need it, and if it will be
used on a continuing basis. If the telco plant is that flaky, it needed
repaired.

There is nothing there suggesting the telco plant is
flaky or needs repair. It just says they do have design
parameter targets, and that good design will adhere to
the specifications.

I had to do a live remote at the Army base and they refused to set up
the copper pair for our feed in time so I took a spare audio board to
the site, and some alligator clips. I dialed the cleanest phone line to
the station and connected the transformer coupled line output to the
phone line, then hung up the phone. The transformer had no trouble with
the DC bias, and the feed worked. They threw a fit when they found out,
but the General was happy that the feed worked.

Your point being? (Other than chest pounding?)

Sigh. You are just being an ass. The point was that we fed the same
level we would have on a dedicated pair, in spite of the DC on the
pair. The equipment was designed well enough that it didn't saturate
the transformers on either end. It was within Telco specs for level and
frequency response, as well.

Compared to the noise from a carbon microphone?

It amplifies that too.

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?

They are closer to what the OP wants to do.

The OP is talking about the PSTN, only.

Then explain the difference between feeding a phone line to a
computer for the OP and feeding a phone line to a computer for talk
radio.

They only worried about it while it was 'on Alice'. When it went to
the old lead clad telco lines it was the military's problem, and they
local group didn't care. The only clean phone line to the broadcast
complex went to a boiler room at the far end. Maintenance used it when
they were there for repairs so it was rarely used. The station's lines
all had so much noise that it wasn't funny. Our complaints always got
the same response. "That trunk line is to be replaced in five years, so
you'll just have to live with it." Some had so much RF problems that
the AM radio signal was louder than either party.

So if the problem was the Army (you), why complain about WACS?

Because I have no way of knowing the level they actually supplied to
the Army on that line. Long distance calls were all loud and clear,
while the net feed sucked.

Only because you don't want to hear it. If the phone lines are down
for long, it cost the telco money, too.

Your point being? (Other than chest pounding?)

yawn. You sound like the typical T&R guy who doesn't give a shit
when your feed is down.

You brought up bridging so get your own towels.

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. Something well beyond what was used in
telco. Telco doesn't use redundant systems and combine the outputs to
improve reliability. But then, people rarely were foolish enough to
depend on the telco to provide mission critical communications if
anything else was available.

Your point being? (Other than chest pounding?)

Yawn.

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

--
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.

 

[Michael A. Terrell]

Paul B wrote:

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

Phil is a mental defective who doesn't take his medication. It
doesn't take anything for him to freak out. Just ignore him, or even
better just kill file him so you aren't tempted to reply to him. It
just makes him behave even worse.

So much for 'National Health Care' down under.


--
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.

 

[Floyd L. Davidson]

"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.)

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