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Old November 4th 03, 04:34 AM
Cecil Moore
 
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Roy Lewallen wrote:
What's the mystery? What's the big deal?


Intel has a lot of problems with buses running in the hundreds of MHz
because of the delay in the conductor path between chips. If I tell them
to install a coil in each path instead of a conductor, the delays will
disappear, right? You're pulling my leg, right?

At frequencies where the delay through a coil is a negligible part of
an AC cycle, the delay can be ignored. At frequencies where the delay
through a coil is not a negligible part of an AC cycle, the delay cannot
be ignored and circuit theory will not yield the correct answers. At the
point where the circuit theory error becomes too great, we must switch
to distributed network analysis.

Consider one foot of wire carrying a 1 GHz signal. The phase shift is
greater than 360 degrees. Can we reduce the phase shift to zero by
installing a coil over that one foot length? You *are* pulling my leg,
right?

All coils have delays. Sometimes those delays are negligible. Sometimes
they are not. The delay through a 75m mobile loading coil is NOT negligible.
That assumption causes errors. The phase delay through a coil is approximately
the same as the section of line replaced by the coil. For an 80m loading coil,
that delay is around 80 degrees or the equivalent of 57 feet of wire. Otherwise,
the forward and reflected currents on the antenna would not have the proper phase.
--
73, Cecil http://www.qsl.net/w5dxp



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