Getting matching transformer from telephone

Really? Minorities were allowed to use them back then?

"

I think he is referring to a part of the world that is about to adopt sharia law..

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.

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 :-))

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

Hi Russell,

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.

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.

On Sat 03 Jan 01:27, Phil Allison wrote

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

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.

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. .

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?

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 (£32)

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 £20

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.

terrorized....in my society I don't need to brag about having experience

Don't give me that pile of crap, Roy. It may be messy, but defense is always right. I have a mop.

Like I said, you'd shit if you so much as saw one in the display case. If you're always being assaulted by gun carrying thugs, why don't you move? I certainly wouldn't be around for the second time.

What a candy-assed loon!

On Mon 29 Dec 15:36, Eeyore wrote

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.

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:

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.

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)

(b) an analogue to digital interface Behringer UCA202 for £20

(C) or something which combines the two.

My post about this is at:

news:Xns9B8A15B4A335B74C1H4@216.151.153.41 Google Groups:

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

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

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.

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. :(

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" :)...

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