Instruction manual

1720/1721
1-1
Section 1
Introduction and Specifications
The TEKTRONIX 1720/1721 is an 8-1/2”--wide by 5-1/4”--high Vectorscope,
weighing 8-1/2 pounds. Both the 1720 (System M, NTSC) and the 1721
(System I, B, etc., PAL) versions can be powered from an ac source or, with the
addition of a field upgrade kit (1700F10), from 12 Vdc. The crt occupies
approximately two-thirds of the front-panel area, with the control panel taking up
the remainder of the space. Operation is controlled by a Microprocessor that
polls the front-panel switches. Front-panel switches are momentary-touch type
with lighted functional indicators. Some of the switches are also used to select
special functions, which are accessed by holding the switches in until the
Microprocessor recognizes the request.
The signal is displayed on a bright crt capable of displaying one line per frame.
It is of the mesh-type, for better geometry, and uses an internal graticule to
reduce parallax. Variable graticule scale illumination provides even lighting over
the usable graticule area without hot spots or voids, to improve measurement
accuracy and the quality of display pictures. Option 74 provides a P4 (white)
phosphor tube.
Composite video signals, for the Channel A and B Inputs and the External
Reference Signal Input, are brought in through high impedance bridging
loop-throughs, in order to protect the integrity of the signal paths. The input
switching allows for the display of Channel A, Channel B, or both inputs.
Synchronization can be either internal or external.
The 1720/1721 offers a choice of individual displays of vectors or XY or both.
The XY display, with accompanying graticule scale, allows this vectorscope to
be used for stereo audio monitoring. In addition to the usual color bar amplitude
and phase relationships, the vector display can also be used to make differential
gain and phase measurements. The 1721 has the +V display that is used to
check PAL system color encoders. Full 360° phase shift and a test circle are also
included in these vectorscopes.
Stereo audio input for XY display is balanced line through the rear-panel
REMOTE connector.
The 1720/1721, through the Auxiliary function, reacts to Store and Recall
commands from a companion 1730-Series Waveform Monitor, when the two are
interconnected. This provides for storing of up to four front-panel setups that
can be recalled when the Waveform Monitor Recall button is pressed, or a valid
1730-Series Remote ground closure occurs. The Auxiliary function can also take
advantage of the blanking strobe, from the waveform monitor, to unblank the
vectorscope crt for a line select display.