On 1/4/2014 5:40 PM, Ralph Mowery wrote:


snip

As the specs is for a 3.5 db loss, I assume that is if you hook up two
antennas to it, the antennas will have a gain of 3 db at the most, then you
go to the combiner and loose 3.5 db for an overall loss of .5 db.

That is where I don't see stacking two antennas and using that combiner for
more signal strength.


Jeff is correct. Your error is believing the combiner has 3.5db loss.

When splitting a signal, you do have about a 3.5db loss per output,
because the signal is halved plus a bit of additional loss. However,
when combining the signals, the signal is NOT halved, so you don't have
the 3db loss there. You only have about 0.5db loss (more or less,
depending on the quality of the combiner and other factors).

Let's take an example. Since a combiner is just a splitter turned
around, we'll start with the splitter end.

Let's feed 2mw to the input of the splitter. This means each output
gets 1mw (3db loss) (we could use voltage also, but since power is
E^2/R, it's not so straightforward).

So now each leg has 1mw on it.

Now let's turn the splitter around and make it a combiner and feed two
signals, 1mw ea., same frequency, to the inputs to the combiner. Since
this is a totally passive device, the effects are reversible. If the
signals are 180 degrees out of phase, of course the output is 0.
However, if the two signals are in phase with each other, the putout is 2mw.

Note there is no 3db loss in the combiner. But of course this assumed a
"perfect" combiner, with no losses. In reality, the combiner will have
a bit of loss (typically 0.5db as noted above), so the output from the
splitter will be slightly less than 1mw and the output from the combiner
will be slightly less than 2mw.

Does this help clarify things?

And yes, phasing harnesses work the same way. The can be either
splitters or combiners, depending on how they are used. The advantage
is they have less loss; the disadvantage, as noted, is they have a much
narrower effective bandwidth.

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