optimum focus of the
3. Adjust the FOCUS control for
Operation of the INTENSIFIER and CONTRAST
vertical sections of the display.
4. Repeat the two adjustments for best overall focus and
These controls are used to suppress the brightness of the
display baseline when large variations in display brightness
are not desirable; for example, when photographing or view-
ing displays at very slow sweep rates. T h e I N T E N S I F I E R
adjusts the height of the suppressed baseline. The CON-
TRAST adjusts the degree of contrast between the suppressed
If a free running trace is not parallel to the horizontal
portion and the intensified portion of the display.
graticule lines, the trace may be aligned by means of an
internal Trace Rotation adjustment. Refer to the Calibration
The adjustment of the CONTRAST is optional; however,
it is normally set to produce a suppressed portion that is
still visible, so the intensity level of the vertical and hori-
zontal portions of the display are equalized at slow sweep
The INTENSIFIER control is normally operated in the OFF
position, so the display and baseline are intensified. It is
turned on to suppress the baseline at slow sweep rates, in
preparation for display photography. See Fig. 2-6.
The application of any RF signal to the Type 491 is deter-
mined by its frequency and level. Signals between 10 MHz
and 275 MHz are applied to the Band A, BNC connector.
Frequencies from 275 MHz to 2 GHz are applied to the band
B, N-type connector, and band C covers the remaining fre-
quency range from 1.5 GHz to 40 GHz. Signals should be
applied through the standard cables supplied with the ac-
cessories. Cables such as RG 9B/U will give satisfactory per-
formance to approximately 12.4 GHz. Signals in the 12.4
GHz to 40 GHz range are applied to external Waveguide
Mixers which connect through a two-foot coaxial cable and
a Waveguide Mixer Adapter to the input receptacle. The
Waveguide Mixer Adapter replaces the Coaxial Mixer As-
sembly in the input receptacle.
The selection of mixers and adapters for the frequency
coverage is as follows:
1.5 GHz to 12.4 GHz-Plug-in Coaxial Mixer, Tektronix
Part No. 119-0096-00.
12.4 GHz to 40 GHz-Waveguide Mixer Adapter, Tek-
tronix Part No. 119-01 04-00; Coaxial Cable, Tektronix Part
No. 012-0115-00 and one of the following Waveguide Mixers.
U G - 4 1 9 / U 119-0097-00
12.4 GHz to
18.0 GHz to
U G - 5 9 9 / U 119-0099-00
18.0 GHz to