This is a dumb question, but I have to ask......................does this
only show up at the wider I.F. bandwidth settings? If so, this is normal. Do
you have the sweep set to automatic or manual mode? If you have your sweep
set to manual mode and your sweep is set too fast, this can occur.

Pete

"John A" wrote in message
...
Hi All,

My HP8558B has developed a fault. Could anyone advise?

Up to about 4MHz the sweep consists of a distorted 0MHz peak then a
sloping,
noise-free, baseline. Above 4MHz the analyser works fine At a Reference
Level switch setting of -30dB there is about one division of noise nad
signal appear as expected

The distortion of the 0MHz peak and the slope of the 0 to 4MHz section of
the sweep varies with the setting of the Reference Level Switch but the
actual gain settings seem to be correct, once you are above 4MHz. Also odd
single spikes appear in this region at different Ref Level settings

Anything else you need to know?

TIA

John