Rich says:
>With 200-ohms unbalanced in and 50-ohms unbalanced out, it has to
be >a transmission line transformer.
No, it doesn't. It could be done as a conventional transformer with a 2:1
winding ratio. Not that I'd advise it.............not for power anyway,
although for receive type applications, it can be a lot easier to do than
getting the proper transmission line impedance for transmission line
transformer. Some of the small 'binocular' cores are very good at receive
type power levels.
In a correctly working transmission line transformer, the core does very
little at the higher frequencies; my experience suggests that when problems
appear at that end, it's due to leakage flux from the transmission line
imperfections. So for a 50 to 200 ohm xfmr, using 93 ohm coax gives better
answers than twisted wire. At the LF end, then the core is needed to stop
common mode currents. Interestingly, when a balun is used with beads over
the coax for 1:1 unbalanced to balanced, why do the beads at the balanced
end get hotter than those at the unbalanced end? Surely not an unbalanced
displacement current to ground because they're at a higher potential by
cpacitive coupling? One would expect a unipotential gradient across the
ferrite beads.
73
Peter G3RZP
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