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
_______________________________________________
VHFcontesting mailing list
VHFcontesting@contesting.com
http://lists.contesting.com/mailman/listinfo/vhfcontesting
|