Specification; Introduction - Tektronix 485 Instruction Manual

Introduction

The 485/R485 is a general-purpose, environmentalized,
high-performance, portable, wide-band oscilloscope which
has a dual-channel vertical amplifier with selectable input
impedance (DC to 350 MHz bandwidth with 50 £2 input
impedance; DC to 250 MHz bandwidth with 1 M£2 input
impedance). The 485 has a 1 ns sweep rate, stable triggering
to bandwidth limits and calibrated X-Y capabilities.
Delayed sweep has calibrated delay time, can be triggered
after delay and can be displayed with the intensified main
sweep in an alternate sweep switching display. Additional
features are X I 0, X I 00 probe scale factor readout, 8 div
X10 div graticule area, small spot size and high writing rate.
A 20 MHz bandwidth limiter, 1 MHz and 1 kHz fast-rise
calibrator and autofocus are also included. The 50 £2 input
is automatically disconnected from excessive voltages. An
external trigger view feature is also provided. The 485-1 and
485-2 have no external trigger view. The 485-2 has only 50
£2 vertical input impedance.
E L E C T R IC A L C H A R A C TE R IS TIC S
V E R T IC A L D E F L E C T IO N SYSTEM
(2 identical channels)
Selectable Input Impedance
50 £2 within 0.5%. VSWR <1.25:1 on 5 mV/div and
10 m V/div, 1.15:1 from 20 mV to 5 V/div to 350 MHz.
1 M£2 w ithin 1% paralleled by approximately 20 pF.
Bandwidth1 and Risetime2
C A L IB R A T E D 3 ) From 50 £2 Terminated Source
—15°C to + 3 5 °C
From 50 £2 terminated source —15°C to +35°C.
50 £2 DC to at least 350 MHz, 1 ns
1 M£2 DC to at least 250 MHz, 1.4 ns
Bandwidth (BW) measured at — 3 dB down.
2 Risetime calculated from 0.35/BW. From +35°C to +55°C, BW is
300 MHz for 50 ft and 200 MHz for 1 M U .
3See Fig. 1-1 for effect of VA R IA B LE gain control.
REV C. MAR 1979

SPECIFICATION

(V A R IA B L E gain
Input Coupling Selection
AC; DC; GND (provides zero reference, precharges
coupling capacitor, disconnects 50 £2 load in 50 £2
mode).
Lower —3 dB Point (AC coupling from 50
source)
50 £2 input, 1 kHz or less.
1 M£2 input IX , 10 Hz or less.
Deflection Factor
5 mV/div to 5 V/div in 10 calibrated steps (1-2-5
sequence), accurate within 2%. Uncalibrated, continu­
ously variable between steps to at least 12.5 V/div.
Lights at edge of knob skirts indicate correct deflection
factor for IX , 10X and 100X probes.
Gain can be recalibrated at front panel. 1 M£2 BAL is
available at bottom panel to eliminate step attenuator
shift above 10 m V/div, in the 1 M£2 mode.
Display Modes
Channel 1; Alternate; Chopped (approximately 1 MHz
rate); Added; X-Y (CH 1 - Y and CH 2 - X ) ; Channel 2
(+Up or Inverted).
Internal Trigger Source
Normal (displayed signal), Channel 1 or Channel 2
signal.
500
400
300
200
BW,
TYP
MHz
VA
100
50
Percent of CAL Gain
Fig. 1-1. Typical Bandwidth, 50 ft vs. Variable Gain Setting (varies
considerably depending on instrument SNI
Section 1— 485/R485 Service
/
/
ICAL BAh DW IDTH.
50 ft
V IS.
RIABLE C A IN SET!
ING
50% 100%
1-1
£2