Forgot all about those impedance bridges, hybrid
transformers, and circulators/isolaters. Directional
amplifiers.
Took the longest time using long hand [before PSPice] to
figure them out.
My opinion:
In the real world using real materials there is no better
transmittor/receiver setup than shielded cables containing
balanced line where the impedance between the two lines is
at least 3 times lower than the impedance to the shield.
Doesn't easily radiate and is not very susceptible to
outside RFI/EMI. Sadly, cost of cables and connectors
drives the selection process and I end up with coax.
- Robert -
On Mon, 24 Apr 2006 17:11:35 +0100
John Woodgate <[email protected]> wrote:
> In message <[email protected]>, dated Mon, 24
> Apr 2006, Robert A. Macy <[email protected]> writes
>
> >I stand corrected. yes, 600 ohm must be balanced
> because it is less than 377 for each line to infinite
> ground.
> > However, it is universally shoved through coax.
>
> Almost no-one uses 600 ohm audio these days, and those
> that do use it balanced. What is put through
> single-screened cable (not usually called coax) is
> consumer audio, which isn't 600 ohms; it comes from a 2
> kohm or less source into a 10 kohm or greater load. Or at
> least, it should do.
> >
> > - Robert -
> >
> >PS: I still think "voltage" came first. <g>
>
> Even the BBC may have been a bit confused about that 30
> years ago, but once you see that the source and load
> impedances [1] form a balanced bridge, so that the
> common-mode signal does not appear in the differential
> signal, you wonder why anyone ever thought that the
> signal voltages mattered.
>
> Another way of looking at it is to consider whether a
> circuit ceases to be balanced if the signal is turned
> off.
>
> [1] To see this, you need to put an equal impedance in
> each leg at the sending end and an equal impedance in
> each leg at the receiving end. The impedances need not,
> indeed should not, be the same at both ends; the
> sensitivity of the balance to impedance tolerances is
> less if the impedances are very different, e.g. 37.5 ohms
> in each leg at the sending end and 10 kohms in each leg
> at the receiving end.
> --
> OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and
> www.isce.org.uk
> 2006 is YMMVI- Your mileage may vary immensely.
>
> John Woodgate, J M Woodgate and Associates, Rayleigh,
> Essex UK
>
-
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