On Nov 2, 9:15 pm, JIMMIE wrote:
On Nov 2, 5:30 pm, "Dave" wrote:





"JIMMIE" wrote in message

roups.com...

I am trying to measure the width of an S band pulse. The circirt
consist of a transmitter wave guide and the dummy load with two
identical directional couplers mounted abot 4 ft apart. The pulse
width measured at the DC closest to the transmitter is measured at
1.05uS Measure ment is made through the 20 db port on the coupler a 20
db pad, doide detector good from .1MHz to 12Ghz. 100Mhz scope
calibrated in the last week.. Same results with another scope.

the other point of measurement uses the same type DC, connection to
the 20db port then a 3db splitter then 20 db pad then the detector and
pulsewidth measure .96uS. VSWR is 1.17
Other port on the 3db splitter has a 30 db pad

What could account for the difference in pulsewidths at the two ports.

Jimmie

so on the 2nd port there is an extra 3db splitter. have you tried it
without the splitter so the same load is on both ports?

Cant do that

Do the pulses both

look the same shape? Yes

more rolloff on the one on the second port maybe? No

perhaps a lower sample power is changing the diode response, that is the
detector may not be completely linear.

Thats what I was thinking but i didnt think 3db would make that much
difference

when you measure the 2nd one do you

remove the detector from the first port and move it?

yes, same detector used on both ports.

or do you have a 2nd

detector that is always hooked up on the 2nd port? I doubt it 40db of isolation betwen the detector and the waveguide

If you move the detector

maybe it changes the load at that point enough to affect the pulse shape at
the 2nd port?- Hide quoted text -

- Show quoted text -

I thought about that thw extra 3db may make some difference but I cant
take it off without taking the equipment down. I have a variable 100db
attenuator and I think I may do some experiments this weekend and see
what kind of effect changes in power level will have on the measured
pulse width.

Jimmie- Hide quoted text -

- Show quoted text -

Ok, it seems like depends on how much power you are putting into the
detector to start with whether or not another 3db matters.

Nice to know it was set up on the hairy edge like this.

Jimmie