On Mon, 26 Jul 2010 08:11:17 +0100, Peter Chant
wrote:

Paul G. wrote:

The RF isolation transformer I mentioned above is referenced a few
times as a braid breaker. With a suitable toroid transformer (like
what you can pull out of a splitter) you should get very good
isolation and uniform response from VHF to well beyond UHF.

When you say "tiny little torroid" in your previous post I presume you don't
mean small like 1/2" but the really tiny ones that are like beads?


They are about 4mm long, and 4mm in diameter (about 1/8 inch). They
have a very good "mu" throughout their frequency range, same sort of
thing that makes a good audio transformer, but at MUCH higher
frequencies. Same issues of magnetizing inductance & leakage
inductance, loss, etc. The older types of ferrite formulations don't
handle the extreme range of frequencies... so I'm told. 50-1000Mhz is
not that easy to do.
They aren't as small as the old core memory boards... I used to
have a set of boards for a 16KB memory plane, you needed a microscope
to see the ferrite toroids. The hole was just big enough for the 4
tiny wires to pass through the toroid. Students were quite in awe of
how small these things were, and always had a laugh at the puny memory
size. It was being used for real time video analysis in the '70's,
something that was then very difficult. It was handled by a CDC
mainframe, an ECL logic computer. The mainframe had its own core
memory, much bigger in capacity, and much faster (see
http://en.wikipedia.org/wiki/Magnetic_core_memory ).
The ferrite cores used in memory are unsuitable for RF.

Paul G.