Instructions

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allowing potential images of signals at the reference level to exceed the noise floor by a user-
defined amount before action is initiated.
The Threshold key can be used to set the tolerated image level to be 0dB (default), 3dB, 6dB,
or 12dB above the noise floor with the current RBW for a signal at the reference level.
Data Comparison (D.C.) Modes - General
Two alternative sweep modes are available that provide a different balance between sweep
speed and image rejection. These sweep methods use data comparison techniques to reject
images and can have advantages over Normal mode in specific situations.
Subject to specific criteria, the IRR can be greater than the display range of the analyzer
resulting in complete suppression of the image.
The technique involves comparing data from two or more sweeps that have been subject to
different frequency mixing offsets. Because the data points are captured at different times, this
technique gives poor results when the signal level is varying.
A further problem exists in terms of the frequency offset used. If two real signals exist that are
spaced by a particular multiple of the frequency offset, the data comparison will fail and the
image will not be supressed. This problem exists not just for signals at the exact frequency
spacing but for signals spaced at that frequency +/-(2 x RBW).
Useful improvements can be made by using multiple sweeps with multiple offsets, however this
slows the sweep rate down still further and may still give erroneous results where multiple
signals exist within the span of the frequency offset values.
 N.B. The Normal sweep mode of the PSA Series 5 uses combined analog and digital
techniques which provides image rejection in real time and does not suffer from either of
the problems discussed above.
Where the user is confident that neither rapidly varying signals, nor multiple large signals
spaced close to the frequency offset(s) are likely to be a problem, data comparison can give a
higher level of IRR than other methods.
D.C. Mode 1
This mode provides perfect rejection of images for signals of constant level subject to a specific
criterion. The sweep speed will become slightly slower for spans below 50MHz (and by a
maximum factor of two for spans below 20MHz), but will be similar to Normal sweep mode for
wider spans.
The criterion for image rejection is that there are no signals within the span that are 40MHz +/-
(2 x RBW) apart. Any such signals will create an image whose magnitude depends upon how
close the signal spacing is to 40MHz. Signals not spaced 40MHz +/- (2 x RBW) apart will not
create an image.
The minimum frequency in D.C. Mode 1 is 30MHz (rather than 10MHz when in Normal mode).
D.C. Mode 2
This mode provides perfect rejection of images for signals of constant level subject to another
specific criterion. The sweep speed will be slower for spans below 50MHz (halving the speed
for a span of 20MHz and quartering it for spans of 2MHz and below) but will be similar to
Normal sweep modes for wider spans.
The criterion for image rejection is that there are no signals within the span that are 40MHz +/-
(2 x RBW) apart simultaneously with signals that are spaced 32 MHz +/- (2 x RBW) apart. This
is an unlikely situation to occur and is consequently “safer” in terms of image rejection than D.C.
Mode 1.
The minimum frequency in D.C. Mode 1 is 30MHz (rather than 10MHz when in Normal mode).
Spurii Reduction