Frequency Stepping Resolution; Triggered Burst And Gate; Internal Trigger Generator - Metrix GX1010 Notice De Fonctionnement

minimum trigger pulse width is 1ms and the repetition rate should be >(1·1 x sweep time
+5)ms.
In MAN/REMOTE mode a single sweep is initiated by each press of the MAN/SYNC key or
by each remote command. If the MAN/SYNC key is pressed again during a slow sweep
(continuous or single sweep) the sweep will be paused at the instantaneous sweep
frequency until MAN/SYNC is pressed again to allow the sweep to continue.

4.3.5. Frequency Stepping Resolution

The generator frequency is stepped, not truly swept, between the BEGin and END
frequencies. The number of discrete frequency steps in a sweep is determined by the ramp
time selected on the sweep edit menu; the size of each step, i.e. the frequency stepping
resolution, is determined by the number of steps and the sweep span. For the fastest
sweeps, 10ms to 200ms, the frequency steps are pre-calculated and output at 125us
intervals; this means that there are 80 discrete steps in a 10ms sweep, 160 in a 20ms
sweep, and so on up to 1600 steps in a 200ms sweep. For slow sweeps, from >200ms up
to 999s, each frequency step is calculated on-the-fly and output every 5ms; this means that
there are 100 steps in a 500ms sweep, 200 in a 1s sweep, and so on up to nearly 200,000
steps in a 999s sweep.
Note that at the fastest sweep rates, with fewest frequency steps (e.g. 10ms sweep) two
effects can occur at extremes of frequency span which are not experienced with
conventional generators. Firstly, if the scan is very wide the frequency changes will be quite
large at each step; if the output is applied to a filter, for example, the response will be a
succession of step-change levels with (at higher frequencies) many cycles of the same
frequency at each step. Secondly, if the begin frequency is less than 800Hz (the ramp rate
for fast sweeps), one or more of the low frequency steps will contain incomplete cycles. In
part, of course, these effects can only be created because of the very wide sweeps that
can be achieved with DDS techniques; analogue generators usually have more restricted
capabilities.
Note also that because the marker pulse duration (from the rear panel TRIG/SWEEP OUT
socket) is that of the nearest frequency step, fast sweep rates with few steps will have
wider marker pulses.
4.4.

Triggered Burst and Gate

In Burst mode a defined number of cycles are generated following each trigger event. This
mode is edge triggered.
In Gated mode the generator runs whenever the gating signal is high. This mode is level
sensitive.
Both Burst and Gated modes can be controlled by either the internal trigger generator, an
external trigger input, by the front panel MAN/SYNC key or by remote control.

4.4.1. Internal Trigger Generator

The internal trigger generator divides down a crystal oscillator to produce a 1:1 square-
wave with a period from 0·02ms (50kHz) to 200s (·005Hz). Generator period entries that
cannot be exactly set are accepted and rounded up to the nearest available value, e.g.
·109ms is rounded to ·12ms. The generator output is available as a TTL level signal at the
rear panel TRIG/SWEEP OUT socket.
In Burst most the rising edge of each cycle of the trigger generator is used to initiate a
burst; the interval between bursts is therefore 0·02ms to 200s as set by the generator
period.
In Gated mode the output of the main generator is gated on whilst the trigger generator
output is high; the duration of the gate is therefore ·01ms to 100s in step with trigger
generator periods of ·02ms to 200s.
24 - II GX1010