chuck wrote:
Thanks for responding, Gary.
Sweep time is something that I had not even been considering, so I
appreciate the info.
From what I can gather about the 7L12, the slowest sweep is 10
mSec/division, or 0.1 second for a complete sweep. That is the sweep
setting Tek says to use for all frequency domain analyses, regardless of
bandwidth. The other sweep settings go from 10 mSec/division to
something like 1 uSec/division, but they are intended for time domain
analyses.
As a reality check on a 0.1 second sweep, I looked at HP's performance
test procedure for the 8552B to see what sweeps they specify for
measuring the 8552B's bandwidth. For the 300 Hz RBW, they list a 0.2
second sweep (I assume that's not 0.2 second/division). Not really too
far from Tek's 0.1 second. Of course, at the narrower bandwidths, HP's
specified sweeps get much slower, as you pointed out. And if it is 0.2
second/division, then there is a profound difference between the Tek and
HP filter designs or I'm missing something big. As I recall, the slower
sweeps are to avoid ringing in the filters, gaussian skirts
notwithstanding.
So maybe the 7L12 doesn't require a storage scope for the 300 Hz RBW?
Sure wish I had access to the Tek Op manual for the 7L12.
73,
Chuck
Hi Chuck,
I have used both the 141T system, and the 7L13. I ditched my 141T because
the 7L5, 7L13, and 7L18 plugins perform better than the equivalent HP plugins
for the 141T system, and are much more compact.
But,
When I was looking into 7L analyzers, I discounted the 7L12. It is too
primative. The minimum you want to do any real work is a 7L13 with a
7633 storage frame. The 7L14 is much better because it has the digital
storage, but it is also twice the price of a good 7L13.
You *will* need a storage scope frame for either the 12, or the 13. The
narrow bandwidth sweeps must be done really slowly. If you try and rush them,
you will lose most of the amplitude information... the filters just cannot
respond quickly. It is a physical reality of narrow band filters.
-Chuck Harris
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