View source for DC503A

{{TM500 | mfg=Tektronix | type=DC503A | function=125 MHz, 8-digit frequency counter | class=counter | image=dc503a.jpg | introduced=1981 | discontinued=1993
|designers=Roland Crop;Jim Geddes
|manuals=
* [[Media:070-2971-00.pdf|DC503A Manual]] (OCR)
* [[Media:TM_9-6625-474-14.pdf|DC503A Military Manual]]
}}
It replaced the [[DC503]] in 1981.

{{BeginSpecs}}
{{Spec|Resolution      | 8 digits}}
{{Spec | Frequency Range | DC (AC coupled: 10 Hz) to ≥125 MHz }}
{{Spec | Impedance | 1 MΩ paralleled by approx. 27 pF}}
{{Spec | Sensitivity | 20 mV<sub>RMS</sub> sine to 100 MHz, 35 mV<sub>RMS</sub> sine to 125 MHz }}
{{Spec | Max Input Voltage | 1× Atten: 200 V<sub>peak</sub>, 400 V<sub>p-p</sub> @ DC − 50 kHz; 200 V<sub>peak</sub>, ≤(20/f) V<sub>p-p</sub> @ 50 kHz − 1.33 MHz; 200 V<sub>peak</sub>, ≤15 V<sub>p-p</sub> @ 1.33 – 125 MHz }}
{{Spec | Max Input Voltage | 5× Atten: 200 V<sub>peak</sub>, 400 V<sub>p-p</sub> @ DC − 5 MHz; 200 V<sub>peak</sub>, ≤(2000/f) V<sub>p-p</sub> @ 5 − 100 MHz; 200 V<sub>peak</sub>, ≤20 V<sub>p-p</sub> @ 100 – 125 MHz }}
{{EndSpecs}}
===Options===
* Opt. 01 — OCXO

==Links==
* [https://www.youtube.com/watch?v=LKyo1sXVjpk Tektronix DC503A Frequency Counter OCXO Mod] by NFM @ YouTube
* [[Media:Component_news_278.pdf|Tek Component News No.278, Feb 1980 – page 13]], ''New Tektronix lever switch''
{{Documents|Link=DC503A}}
{{PatentLinks|DC503A}}

==Rear interface==

<small>
{|
|-
| 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==
<gallery>
dc503a.jpg | DC503A
Tek dc503a on.jpg|DC503A
Tek dc503a left internal.jpg|DC503A left internal
DC503A right.jpg | right internal
DC503A left.jpg  | left internal (Opt.01)
</gallery>

==Components==
{{Parts|DC503A}}