Most people think of a directional coupler as a directional coupler, and a
splitter as a splitter. In reality, the splitter is simply the extreme case
of a directioanl coupler where the coupling factor is 50%.

The fact that it was designed for 75 ohms is somewhat incidental. The
impedance on any of the ports is a function of the impedance on the other
ports. As to phase, it has to be well-behaved or you wouldn't have good
directivity.

Joe
W3JDR


Steve Nosko wrote in message
...
Joe,

Interesting. A splitter as directional coupler for the reverse
direction.... Hmmm Yea... and since the device 'probably' won't be near
75
ohms, that directivity won't be a big issue. What about the phase
response
bandwidth? That's important too. Unfortunately the phase response starts
changing well into the passband, right?...
--
Steve N, K,9;d, c. i My email has no u's.


"Joe Rocci" wrote in message
news:T0eSc.4297$Kv2.4186@trndny09...
Steve,
A decent (not the dollar store variety) CATV splitter has directivity of
about 30 dB from 5Mhz to over 500 MHZ. I think this would do the job.

Joe
W3JDR


Steve Nosko wrote in message
...

"Paul Burridge" wrote in message
...
On Tue, 10 Aug 2004 01:53:44 GMT, "Joe Rocci"
wrote:

Here's an idea that's just whacky enough that it might work...has
anyone
tried it?

If you have a dual-trace scope with enough bandwidth, you might be
able
use
Lissajous patterns. The idea would be to drive the complex load
through
a
directional coupler with fairly good directivity. A sample of the
incident
signal would go into the scope X input and a sample of the
reflected
signal
would go into the Y input. With a pure reactance as a calibration
load,
adjust the X and Y scope gain for a perfect circle on the display.
Replace
the test load with a complex load, and the magnitude and
inclination
of
the
line/oval display can tell you amplitude and phase of the reflected
signal,
from which any other metric can be calculated.

Nice idea, Joe! If it could only be made to work, you'd be a genius.
--


OK Actually, this looks good as long as you have a directional
coupler
for
the frequency of interest! Paul didn't say. (SWR Bridge, actual
bridge,
for lower frequencies) You'll also have to allow for the difference
in
location of the two samples by adjusting the line lengths to the two
scope
probes intil they are both at the same "distance" from the load.
Judging
phase shift from a circle can't be as good as simply looking at the
two
waveforms. The scope horiz gain can be adjusted for some nice number
of
divisions for each half cycle, say 9...
I've got a 100MHz. dual trace storage scope, but any directional
couplers around here only will be down to 130 Mhz at best... I do
also
have
a good bridge for down to 5 MHz., (also about 1 meter worth of stretch
line...so it is possible as long as the power level is within the
bridge
capability.
--
Steve N, K,9;d, c. i My email has no u's.