On Tue, 28 Feb 2006 20:35:01 -0600, Bob Bob wrote:
I suspect there is also another issue whereby the resonant sensor
section is actually absorbing more power than it should and dissipating
it in the resistor.

Hi Bob,

That is why it is there, among other reasons.

The effect of this being a loss of available output
power at the SMA connector.

This is a symptom, and should not be a cause.

To answer you specifically Richard, the PCB is a multilayer fibreglass
thing with a largish ground being under both the output and sensor
striplines.

That is as it should be.

I was surprised that the sensor line was so long and so

On the order of 1.5 cM?

close when I first saw it thinking some major overcoupling might be
occurring. The tracks are maybe 3mm wide and about 1.5mm (edges) apart.

Sounds like a boilerplate design - which is to say right out of some
book or App. Note.

I am thinking also that the 50 ohm output is not being preserved as it
goes past the sensor stripline.

What does that mean?

I think the freq coverage for this model
is about 10.5 to 11.5GHz. Keep in mind that this really is the frist
time I have seen microwave TX's up close so my gut feelings about track
sizes/spacing may be way off.

Check the resistor.

73's
Richard Clark, KB7QHC

Hi Richard

I was surprised that the sensor line was so long and so

On the order of 1.5 cM?

It is a "U shape". The section parallel to the output stripline is maybe
1cm long (going from memory). The leg length may then put the total size
at more like 2cm.

---

I am thinking also that the 50 ohm output is not being preserved as it
goes past the sensor stripline.

What does that mean?

I am suggesting that given the proximity of the sensor section it
presents a significant Z bump. Like I said I dont have a feeling for the
track dimensions for stripline etc at microwave. Not that it wouldnt be
difficult to look it up mind you!

---

I think the freq coverage for this model
is about 10.5 to 11.5GHz. Keep in mind that this really is the frist
time I have seen microwave TX's up close so my gut feelings about track
sizes/spacing may be way off.


Check the resistor.

One of the first things done. At DC of course. Dont think I ever
replaced it. Was considering playing with it last time but since moving
the frequency also bought it back to normal operating conditon I couldnt
see it as a reason.

Cheers Bob VK2YQA

On Wed, 01 Mar 2006 09:19:37 -0600, Bob Bob wrote:

Check the resistor.

One of the first things done. At DC of course. Dont think I ever
replaced it. Was considering playing with it last time but since moving
the frequency also bought it back to normal operating conditon I couldnt
see it as a reason.

Hi Bob,

DC is so remote from the application as to be only an approximation.
There's also the prospects of reactance to consider too. When you say
you can see a frequency dependency, you are almost guaranteeing that
"tuning" has been injected into an otherwise wideband design.

From your position in the company you have two paths:
1. Announce the design is FUBAR, or
2. Find an ad-hoc solution and forget theory because you are in no
position to re-engineer the design.

#2 is a dangerous path to take for the sake of the company's
perspective, although it may be more politic if the design department
is populated with prima-donnas.

#1 will accomplish one of two things, the design will be corrected, or
you will be educated - possibly both. Most designers appreciate
hearing what your experience has revealed. Most of my techs enjoyed
pounding my designs to find the weak seams. One fellow had a small
transistor radio that he would put on top of the microprocessor to
listen to the software running. He could always tell when one of my
patches went south.

73's
Richard Clark, KB7QHC