On Tue, 5 Oct 2004 15:59:32 -0500, "John Smith"
wrote:

|
|"Wes Stewart" wrote in message
.. .
| On Mon, 4 Oct 2004 20:58:07 -0500, "John Smith"
| wrote:
|
| Second. I believe that you need to determine the parameters of your
| directional coupler. As Richard pointed out, your B1/A1 numbers are
| pretty unstable.
|
| So here's what I recommend. First verify that the "A" and "B" probes
| read the same thing when connected to the same source.
|
|I put the oscillator to the center of the HP Power Splitter. I then put a
|probe tee on each of the splitter outputs followed by a 50 Ohm terminator.
|The difference between the A and B channels was maybe a needle's width.
|Reversing the splitter made no difference. Swapping the terminators made no
|difference.

Excellent.
|
|
| Then put your
| pad right at the input connector of the coupler. Terminate the
| reverse port and connect your VVM "A" probe to the ouput connector and
| the "B" probe to the forward port.
|
| The ratio reading is the forward coupling factor of the directional
| coupler. Vary the frequency and see how this changes and note some
| values. Move the "B" probe to the reverse port and terminate the
| forward port. Note the readings at the same frequency.
|
|From 350 MHz to 450 MHz the forward port coupling was -25.9 dB to -26.2 dB.

Okay. Not per nameplate, but now you know.
|
| Reverse the input and output ports and repeat the measurements.
| Ideally, the data sets will track closely.
|
|
|I got the same here within about a tenth of a dB.

Great.
|
|
| If they don't then you
| have a problem. Serious differences might indicate damage to the
| internal terminations. This assumes that this is a true dual coupler
| and not single line coupler with the termination applied to the unused
| port externally.
|
| If the numbers are consistant, then you can determine the directivity
| by computing the ratio between the two readings on a given port when
| the coupler is reversed.

You still need to do this.

|
| I'm going to stop here and assume you understand the consquences of
| poor directivity on measurement accuracy. If you don't then I can
| expound further later.
|
| Wes
|
|
|I guess it looks okay. Thanks, Wes.

You're welcome.

Wes