[mythtv-users] Coax splitters - how painful are they?
beww at beww.org
Tue Sep 25 22:11:29 UTC 2007
Guillaume Filion wrote:
> Brian Wood a écrit :
>> A "perfect" two-way splitter would have 3db. loss. Since nothing is
>> perfect in this world, most splitters actually lose 3.5db. per leg for a
>> two-way split, and 7db. for a four-way.
> I think that I remember being told that there's a resistor in the
> splitter to ajust the impedance. That way, a two way splitter would give
> 1/3 of the signal in each leg -- with 1/3 lost in the resistor.
> Is my memory serving me right?
No, at least not for "hybrid splitters" made in the last half-century.
They use a transformer-like device to make the power split, and depend
on external terminations to keep the impedances correct (as opposed to a
You might be referring to what were called "back matched taps" used
early in the CATV game, they did in fact throw away some power in a
termination to keep things matched properly.
In case some folks have missed it, a perfect two-way split with no
device losses would be a 3db. "loss" to each leg. Actually nothing would
be "lost" as all the power would be accounted for. In other words: If I
have a cable with +30dbmv. comoing out of it, and I take away half of
the signal power, I will then have +27dbmv., NOT +15dbmv.
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