DC503A

Manuals – Specifications – Links – Pictures

The Tektronix DC503A is a 125 MHz, 8-digit frequency counter plug-in for the TM500 system.

It replaced the DC503 in 1981.

Key Specifications

Resolution	8 digits
Frequency Range	DC (AC coupled: 10 Hz) to ≥125 MHz
Impedance	1 MΩ paralleled by approx. 27 pF
Sensitivity	20 mVRMS sine to 100 MHz, 35 mVRMS sine to 125 MHz
Max Input Voltage	1× Atten: 200 Vpeak, 400 Vp-p @ DC − 50 kHz; 200 Vpeak, ≤(20/f) Vp-p @ 50 kHz − 1.33 MHz; 200 Vpeak, ≤15 Vp-p @ 1.33 – 125 MHz
Max Input Voltage	5× Atten: 200 Vpeak, 400 Vp-p @ DC − 5 MHz; 200 Vpeak, ≤(2000/f) Vp-p @ 5 − 100 MHz; 200 Vpeak, ≤20 Vp-p @ 100 – 125 MHz

Options

• Opt. 01 — OCXO

Links

• Tektronix DC503A Frequency Counter OCXO Mod by NFM @ YouTube
• Tek Component News No.278, Feb 1980 – page 13, New Tektronix lever switch

Rear interface

27B − Decimal point
26B – Remote Start	26A − /Reset
	25A − TS1 (digit select 1, MSD)
24B − Scan clock out
23B − Overflow
22B − Ch.B Level	22A − Ch.A Level
21B − BCD out 2	21A − TTL Clock Input
20B − BCD out 8	20A − BCD out 4
19B − Latch Out (Data Good)	19A − BCD out 1
17B – Ch B Input	17A – Ch A Input GND
16B – Ch B Input GND	16A − Ch A Input
15B – 10 MHz Ref Out	15A – Clock GND
	14A − External Clock In

Internals

The DC503A is implemeted in a mix of ECL, TTL, and MOS ICs. uses an LS7031 6-digit counter IC, and two 74S288 PROMs that encode decimal point position and annunciators.

Pictures

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  DC503A

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  DC503A

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  DC503A left internal

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  right internal

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  left internal (Opt.01)

Components

Some Parts Used in the DC503A