"Wes Stewart" wrote in message
...
On Mon, 4 Oct 2004 16:45:31 -0500, "John Smith"
wrote:

Freq (MHz) Impedance (Ohms)

410 46.4 + 6.0i (50 Ohm terminator)

380 9.7 - 12.5
390 3.5 - 5.7
400 5.1 + 1.3i
410 5.1 + 6.5i
415 4.0 + 10.0i
425 2.5 + 15.7i


| 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


Okay. I repeated the test using an HP 355C attenuator set for 10 dB and at
400 MHz got 4 + 3i on the antenna. I also checked my 50 Ohm network
terminator with this setup and it measured 44 + 4i. The data are different,
but they're not an order of magnitude different, at least.

So, although my measurements aren't repeatable, they are sloppily
consistent. That is, although I can't say exactly what the antenna impedance
is with confidence, I am beginning to believe that it really is very low in
impedance. Am I drawing an erroneous conclusion too early? I can wait a
little longer to draw an erroneous conclusion.

John