Topband: Rx power splitter
richard at karlquist.com
Thu Feb 7 15:21:04 EST 2008
Lee K7TJR wrote:
> Pete: I suggest you use a Magic Tee combiner backwards. To understand it
> you can Google magic tee and look at the pages by Mike Ellis. W8JI has
> some stuff on them too. I use 7 of them in my one array and they work
> quite well. You only need two transformer cores and a resistor 2 times
> your cable impedance. You could use 10 turns each side on an FT37-43
> toroid or 3 turns each side of the 2873000202 binocular core for the Tee.
> Lee K7TJR Oregon
Lee mentions a Magic Tee combiner (AKA 180 degree hybrid), but he
is actually telling you to build a 0 degree power divider,
which is a superset of a magic tee, and therefore requires two
two transformers. For your purposes, a bare 180 degree hybrid
would work just as well. After all, you don't care if the signals to the
receivers are 180 degrees out of phase. The advantage of the bare
180 degree hybrid is that only ONE transformer is required.
You do need to use an unequal number of turns on the two windings,
which is seldom if ever mentioned in any tutorials on making hybrids.
If the antenna and receivers are the same impedance, the turns
ratio is 1:1.4 (impedance ratio 1:2), with the antenna across the winding
with fewer turns, and with each end of the other winding connected to a
receiver. The center tap of the receiver winding goes to ground through a
resistor of half the receiver impedance. If the antenna is 75
ohms and the receivers are 50 ohms, change the turns ratio to
1:1.15 (impedance ratio 1:1.33). I have been building homebrew
180 degree hybrids with unequal turns ratios for years and they
have worked perfectly for me.
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