Now I understand, thanks.
> On Tue, Apr 12, 2005 at 01:52:13PM -0400, David L. Martin wrote:
> > > On Tue, Apr 12, 2005 at 01:48:34PM -0400, David Martin wrote:
> > > > Looking at the specs from several Bias Tee manufacturers, I am
puzzled
> > > > by the "Return Loss" spec. Does anyone know what this refers to???
> > > > This is typically a pretty high number 10 -> 30 db.
> > >
> > > The amount of power reflected from either the input or output.
The higher
> > > the number - the closer to a 1:1 SWR you are seeing.
> >
> > I still don't have it.
> > You mean power reflected across the T or from the T. If it is from the
> > T then wouldn't that be bad? If it is across the T the wouldn't 10 ->
> > 30db be bad also?
>
> Imagine that you have a perfect load on the output of the device. Put a
> directional wattmeter on the input and put some power through it.
>
> The return loss is essentially the difference between the input power to
> the bias tee and the amount of power reflected back from the input.
>
> So - if you put one watt into the bias tee and 1 watt gets reflected
> back - it's time to buy a new bias tee. If 1/100th the power gets
> reflected (20 db down) - then it is working fine.
>
> The same measurement can be made on the output looking back into the tee.
>
> If you call the input port 1 and the output port 2, then S11 is the input
> return loss, S22 is the return loss on the output and S12 is the loss
> through the device.
>
> Tree N6TR
> tree@kkn.net
>
>
--
David L. Martin
w0snj@arrl.net
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