I'm not sure if this faut I describe below accounts for the curious
problems I've been experiencing, but it might be relevant, possibly...
When I'm displaying (in rectangular mode as opposed to polar) a sweep
from 4Mhz to 1.3Ghz I get a pretty flat horizontal line right across
the screen as perhaps you might expect (with no load attached to the
test bridge and the port left open. Now if I stick my finger inside
this port and probe around; I get very little response from the trace.
Likewise if I now short the port, there's very little variation in the
trace. I'd have thought making major changes to the electrical
characteristics at the test port would give rise to some pretty extreme
waveform changes; but this isn't the case. It seems like it's missing a
large amount of senstitivity and I can only think maybe the y-amplifier
might have gone low-gain. Does that make any kind of sense in terms of
the problem I'm describing? Can anyone suggest a test to confirm or
eliminate this possibility?
Thanks,
Paul