----- Original Message -----
From: "Dan Sawyer" <dansawyer@earthlink.net>
To: "amps" <amps@contesting.com>
Sent: Friday, November 18, 2005 4:10 PM
Subject: [Amps] bi-directional coupler question
> All,
>
> This journey started several months ago with the purchase on an 8405a to
> measure an antenna. One of the items listed at that time was a
> bi-directional coupler. Finally I have found one and am beginning to
> experiment. The first readings seem to show that the coupler may be
> supplying readings that are out of phase? Direct input to the coupler
> terminated in a 50 ohm dummy load produce readings that appear to be 90
Hi Dan,
A bi-directional coupler has a mainline input and mainline output. The
other two ports are the coupled ports. One is zero degrees phase shift and
the other is 180 degrees phase shift because it is looking at the reflected
power coming back to the mainline output. It is very useful because you
can see forward and reflected at the same time using two meters.
If you are seeing 90 degrees phase shift then you may have a quadrature
hybrid which is a four port device that will give you two outputs that are
90 degrees out of phase when any port is fed and the opposite port is
terminated.
A 180 degree hybrid is similar however in this case there are two ports
that will be in phase when the opposite is terminated and two that will
be 180 degrees out. A bi-directional coupler is essentially a special type
of 180 degree hybrid.
Hope that helps, Mike
> degrees out of phase. Is this correct? Is it a coupler design issue? I
> am a novice in this area so I am not sure what is normal and what is not.
>
> Is this one of those cases where the 8505 is biased to read 0 phase
> angle into a known termination and then read the difference in the
> circuit under test?
>
> Thanks in advance - Dan
> _______________________________________________
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