On Mon, 4 Oct 2004 16:45:31 -0500, "John Smith"
wrote:

|Hi, Wes -
|
|
|"Wes Stewart" wrote in message
.. .
| On Mon, 4 Oct 2004 15:19:41 -0500, "John Smith"
| wrote:
|
| John,
|
| First of all you are to be commended for running these experiments.
| Without a bit more study of your situation I can't comment too much
| but I wanted to throw out a couple of quick ideas.
|
| 1) Do you have the VVM probes terminated in 50 ohm?
|
|
|Yes. They came witht the kit and are called terminators. They are 50 Ohms
|each.

Okay.
|
|
| 2) If you don't have the line stretcher as in Fig 7 of the note, are
| you recalibrating at each test frequency?
|
|
|I do not have the stretcher. I recalibrate at every frequency change.
|
Understood.
|
| 3) How well is your signal source terminated, in other words do you
| know its source match?
|
|
|I only know that the signal source is an HP 3200B. It directly feeds the
|Narda dual directional coupler through a few feet of RG58.

If I remember that correctly the '3200 is nothing but a p-p oscillator
and a waveguide-below-cutoff probe. If your VVM reference probe
readings are changing much between frequencies and/or
calibration/measurement, try a 6 or 10 dB pad right on the generator
output and see what happens.

When you're calibrating using a short, the source Z has really got to
be nailed down.

Wes