Paul & Steve,

Steve,
I'm pretty confident that the phase shift will be constant and can be
calibrated out. If not, it can be made irrelevant by using two splitters,
one for the forward path sample and one for the return path sample.

Paul,
The idea is to use the splitter 'backwards"; drive the RF into one of the
splitter legs and feed the load through the common port. Assuming good
directivity, any RF coming out of the other splitter leg must be reflected
energy. If you put a sample of the forward energy into a scope's X input
(horizontal) and a sample of the reflected energy into the Y input
(vertical), you will get an elliptical display called a Lissajous pattern.
If X and Y are equal in magnitude and exactly 90 deg out of phase, this
will be a perfect circle. Any other phase angle will result in a elliptical
pattern whose inclination angle relative to the X axis (or Y axis) is a
function of the phase angle. The length of the ellipse is a function of the
magnitude. This is classic stuff...look it up if you're not familiar with
it.

Joe
W3JDR


Paul Burridge wrote in message
...
On Thu, 12 Aug 2004 15:32:00 -0500, "Steve Nosko"
wrote:


Lets think about this phase thing, however. As long as there is the
proper
phase cancellation _in_ the splitter, it will balance. This doesn't mean
that it is flat, does it? You'll be sampling the forward power somehow
and
the reverse power with one of these and you need to have them both
constant
with respect to each other--otherwise you cant measure phase.. If the
fwd
sampler is the same thing do you get matching characteristics (ignore
secondary imperfections for now). I don't know how good ones are made,
so I
have know first hand knowledge.

Let's assume for one moment the splitter idea would function
acceptably as a directional coupler for this purpose. What's next in
the block diagram? Phase comparitor? DC amp?

--

"What is now proved was once only imagin'd." - William Blake, 1793.