You can get excellent feedline isolation by using
a Mini-Circuits T1-6 transformer. There is very
little insertion loss and the capacitance from primary
to secondary is very small. Because of the extremely
small size, it is probably smaller than anything you
would homebrew, and anyway, the price of T1-6 is low.
Dan Zimmerman N3OX wrote:
> Any reason not to use a 1:1 transformer wound on a Fair-Rite
> 2873000202 instead of a conventional feedline choke to get extra
> common mode impedance for my flag feedline?
> I'm not phasing it with anything so I don't have to worry about
> accidental phase inversion.
> Is insertion loss an issue?
> I wound the flag transformer on one of these cores and measured
> (inaccurately I'm sure) about 10pF between the primary and secondary
> windings. I'm sure I can do better with just two turns on either
> side, so it seems like a cheap way to get an extra few thousand ohms
> of isolation.
> Any thoughts appreciated. I've got some nasty local QRM this season,
> unfortunately, so anything I can do to keep the flag pattern clean is
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