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






Gary Schafer wrote:
On Wed, 18 May 2005 19:04:44 -0400, chuck wrote:


I'm in the market for a used spectrum analyzer like the 7L12
or the HP 141-T. One important use will be to make two-tone
IMD measurements on HF SSB transmitters. I am concerned that
with tone separations on the order of one kHz, the 7L12 may
not have sufficient bandwidth in the 300 Hz mode to resolve
adjacent IMD products expected to differ in amplitude by 40
dB or more.

Has anyone on the group used a 7L12 for this purpose and is
the 300 Hz RBW sufficiently narrow?

There seems little doubt that the 141, with 10 Hz or 100 Hz
RBW, will handle this.

Many thanks in advance.

Chuck
NT3G


I have never played with a 7L12 but do have a 141t. 300hz bandwidth
will work. The best resolution on the 141t is 100hz. There is a 10 hz
video filter but the video filter does no good for resolution. It only
gets rid of noise. The biggest problem that I can imagine with the
7L12 would be whether or not your scope has some kind of storage or
long persistency on the tube. To look at 300 hz bandwidth you need a
very slow sweep speed on the scan. If there is no storage you will not
be able to see it.

73
Gary K4FMX