On Sat, 08 Oct 2005 14:13:02 GMT, Cecil Moore wrote:

Owen Duffy wrote:
An extension of that thinking is in the proposition that I have seen
that a Bird 43 cannot give valid readings unless there is at least a
quarter wave of 50 ohm line on each side of itself. In this case, the
magnitude of significantly affected line seems to be 25%, someone
else's is 2%, can they both be correct?

I think if you will recheck that posting you will find the assertion

Cecil, it is someone else who has on a number of occasions suggested
the quarter wave thing in email correspondence, and here in postings.

My suggestion is that the sampler inside a Bird 43 coupler section is
sufficiently far inside the 50 ohm coupler line to provide
measurements within the instrument's stated accuracy of what is
happening within the 50 ohm coupler, irrespective of whether, for
instance, a 75 ohm line is attached to the coupler on the load side.

The measurements of what is happening within the Bird 43 coupler could
then be used to model what is happening on the adjacent line, having
regard for any Zo changes, loss, length etc.

Owen
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