[VHFcontesting] Biat Tee return loss

[David L. Martin]

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 at kkn.net
> 
> 

-- 
David L. Martin
w0snj at arrl.net