Hi Allen:
I'll take a shot at this one! (At one time I dealt with high-
fidelity high-frequency signals where the effects of connectors
could be observed in the waveforms.)
The ideal transmission line is terminated at both ends with its
characteristic impedance.
In some circumstances, you can "cheat" by not providing a
termination (i.e., open or short) at either the source end or
the load end, depending on what you want to accomplish.
If you terminate at the load end, then no standing waves and no
reflections back to the source. So, the source can be any
impedance without degrading the signal, and you get twice the
voltage.
If you terminate at the source end, then you get a standing wave,
and reflections. The reflections are terminated in the source
impedance and don't distort the pulse at the source.
I presume this is your situation -- terminating at the source.
I'm afraid I have no idea of what is radiated from the transmission
line, but I would guess that it would be a lot because of the
standing wave.
If you change impedance, you get standing waves or reflections,
but not as much amplitude as a short or open. There are
impedance-matching attenuators which act as a termination for
one transmission line and as a source impedance for the other
transmission line. Lossy.
There is leakage from transmission lines. I would expect rather
high leakage from a PWB transmission line (compared to coax).
As one colleague once stated, the whole world is a transmission
line. In fact, he calculated the characteristic impedance between
the earth and the moon! 377 ohms???
Best regards,
Rich
-------------------------------------------------------------
Richard Nute Product Safety Engineer
Hewlett-Packard Company Product Regulations Group
AiO Division Tel : +1 619 655 3329
Effective 6/12/99: +1 858 655 3329
16399 West Bernardo Drive FAX : +1 619 655 4979
Effective 6/12/99: +1 858 655 4979
San Diego, California 92127 e-mail: [email protected]
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