Getting matching transformer from telephone

Speaking of cretins!

The chart is from Bell System documentation (which I cited in another article). If you think the frequency has nothing to do with the characteristic impedance, argue with Bell Labs.

ADSL is based on 100 Ohm impedance for very good reasons. One of them being the frequencies used...

Did you see where it said above... "Telephone cable". Not all telephone cable can run ADSL. (And no you don't "just adjust the line gain".)

The definition of on/off hook supervision has not changed, and that makes it exceedingly relevant.

Not necessarily. Some do have transformers.

You falsely claimed it was otherwise. Seems *you* are the one with a lack of "know" about this topic.

That is true, but doesn't mean what you apparently think it does.

A mismatch at the distant end will result in echo, and if the distance (no matter whether it is traversed via metallic cable, fiber, microwave or satellite) is far enough to delay the echo long enough, it will be heard as an echo by the near end user.

Typical local calls usually have a low echo return delay, while long distance will be higher. However, that is not always the case and I can demonstrate examples of local calls that are routed over satellite systems (meaning the echo delay is necessarily very close to 400-500 milliseconds). Those calls require echo cancellation, because even if the echo is 30 dB down, it is still very annoying when there is that much delay.

using

sound card

transformer. In

incorrectly

Which would doubly load the line silly.

What is required here is what was typically once called a bridging transformer. Audio doesn't use signal transformers much these days except the tube nuts. Or, come to that, an active 'balun' with AC coupling to keep the line DC out. 2 caps, 4 resistors, a single op-amp and maybe even battery powered. Plus some protection diodes for good measure. 48V is a bit iffy even after a cap.

Graham

In civilised parts of the world with proper infrastructure it can.

Graham

Such as ?

Graham

It isn't. Not for about 45 years.

Graham

In the right situation, someone might actually consider you as credible too. Just not in the reality that we all live in. We call it the real world. In it, you and credibility do not homogenize together. That is one water your oily ass won't mix with.

inductors).

Is it really so goddamned hard to accept the fact that such items do exist?

Probably just as hard it is to accept the fact that you are a self denying, US hating retard.

using

card

Tell us about how different a 600:600 transformer is from a 10k:10k transformer, eh?

incorrectly

What he probably wants is a 1:1 transformer.

What ?

Look, I've designed line interfaces FFS. For Xerox. I've already mentioned it once.

Graham

using

card

In

incorrectly

That would be true *if* he wanted to load the circuit down to 600 Ohms, but he almost certainly does not. Doing so would reduce the level available to the telephone set user by 3 dB. What he probably wants to do is bridge across the "600 Ohm" telephone set with something that is at least 6000 Ohms.

If the line input this transformer is attached to is 6k Ohms or higher, a 1:1 transformer will do. Otherwise he has two choices, one of which is a transformer with a more suitable turns ratio, which will provide maximum signal level. However, at that point there is almost certainly an excess of gain, and hence another possible solution is to merely put a pair of resistors in series with the side connecting to the telephone set, or on the side of the transformer connecting to his recording device (if it is single ended, it requires only a single resistor).

Rather different to 2k I think you'll agree.

Ribbons are FAR lower. Maybe 50 ohms AFTER the transformer !

And Pin 1 on an XLR is ALWAYS the cable shield. It may also be GROUND - but that's another story. It certainly isn't used to provide phantom power under ANY circumstances. And the last time I came across a centre tapped transformer in pro-audio was 35 years ago. It caused a bloody nuisance too. Modern balanced audio circuits are 'floating'. The centre tap provides ZERO advantage.

I now expect you to make an idiot of yourself trying to refute that one.

Graham

How would you know that?

You are DimBulb and I claim my £1000.

Graham

Have you even the tiniest clue yourself ?

Graham

Jesus Wept !

Graham