Instructions

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Distortion and non-linearities within the analog circuitry of the instrument can create very low
level signals that could be visible for settings where the noise floor is very low. These are
referred to as Spurii.
DC Modes have the further advantage of reducing Spurii.
7.5.3 Revealing the Image
The multiple IF frequencies used within the PSA Series 5 can result in a group of up to three
images appearing close together at around 20MHz below the signal frequency. If this is outside
of the current span, the image(s) will not be visible.
However, images can exist of signals that are outside of the span. For example, a large signal
at 433MHz and a span set at 400MHz to 420MHz could result in a potentially visible image(s)
even though the signal itself would not be visible.
With wide RBWs (1MHz and above) the noise floor is high enough that images are unlikely to
be visible above the noise. Similarly signals well below the reference level will not create a
visible image because the IRR will supress the image to below the noise floor.
Images become a problem when it is unclear whether an apparent small signal is “real” or just
an image of a large signal circa 20MHz above.
The user can check whether an image exists by pressing the key marked “Reveal Images” (see
section 4.3.5). This causes the analyzer to operate briefly with image rejection turned off
resulting in the level of any images increasing by the IRR value.
7.5.4 Sweep Times
Sweep times are a function of frequency span and RBW/VBW. Generally the sweep time
varies in a direct relationship with the span and an inverse relationship with the RBW. For
narrow spans and/or wide RBWs, the minimum sweep time of just under 0.1 seconds will apply.
Note, however, that the maximum display update rate is limited to about five per second.
Where the sweep time is significantly longer than the minimum, the user is able to decrease the
sweep time by a target factor of 2, 5 or 10 (F1, F2 or F3) from the Sweep Time menu (see
section 4.1.6). This has a relatively small effect upon signal amplitude accuracy and can be
very useful when faster response is important.
The degree of speed up actually achieved is dependent primarily on the RBW. For a 1kHz
RBW and 1MHz span the normal sweep time is 12.8 seconds, but this can be reduced to 1.2
seconds by selecting F3. However for wider RBWs the degree of speed up is reduced.
In D.C.1 and D.C.2 sweep modes, the degree of speed up will be limited even at narrow RBW
settings.