Dan,
your original posting says the shift you are getting is frequency dependent.
Your last posting says it is not. Which one I read wrong?
Thks
Ivan
"dansawyeror" wrote in message
...
Frank,
The bi-directional coupler is a machined block about 1 x 3 x 5. The inside
is a
straight through line, the pickups are simply terminated one loop lines.
It is a
UHF coupler that works reasonably down to 2 meters. When I configure this
to
look at the forward and reflected 'open' circuit case they are not in
phase.
Reflected lags forward by about 40 degrees. (I checked the connection
delay and
this is not a cable issue.) This is frequency independent. Shorting the
output
reverses this relationship. The outputs are terminated in 50 Ohms so I
conclude
it is a 50 Ohm device. When I terminate the device in 50 Ohms the forward
and
reflected outputs are out of phase by about 140 degrees.
What is the significance a non frequency dependent phase shift between
forward
and reflected? This shift is frequency independent.
Thanks - Dan kb0qil
Frank wrote:
Your answer to the question about bidirectional couplers was they do not
compensate for phase shift. Let me ask it again:
Do the measuring ports of a bi-directional coupler accurately represent
or
preserve the relative phases of the signal?
To put it another way is the phase shift of the driving and reflected
signals changed by the same about?
Thanks - Dan kb0qil
The phases seen at each coupled port should be identical to the phase of
the
forward and reflected signals. This is easily verifiable, and frequency
independant, as follows:
No load -- forward and reverse amplitudes equal, and in phase;
Short circuit at output -- forward and reverse amplitudes equal, and 180
degrees phase difference;
50 ohm load -- reverse than forward by = specified coupler
directivity,
and phase difference can 0 theta +/ 180.
This is only true if the frequencies are low enough such that the
standards
do not require quantification by the use of "Standard definitions" --
see
www.vnahelp.com.
Regards,
Frank