Extech Instruments 381235 User Manual

User's Guide

Frequency Counter

Model 381235

Introduction

Congratulations on your purchase of Extech’s Frequency Counter. This meter will measure
frequency to 2.5GHz using test leads or the optional RF antenna. This professional meter,
with proper care, will provide years of safe reliable service.

2

Specifications

General Specifications

Display 0.5” (13mm) 8-digit LCD
Functions Frequency, Data Hold, Relative, Max/Min/Avg & Period
Input connectors BNC female
Meter housing Durable ABS plastic
Operating conditions 32 to 122oF (0 to 50oC); < 90% RH
Power supply 4 x 1.5V AA cells

AC adapter (option) 9VDC, 300 to 500mA (center socket pin positive)
Dimensions; weight 6.8 x 3.1 x 1.4” (173 x 80 x 35mm); 0.75 lbs (340g)

Electrical Specifications

Period range Ch. C: 10MHz
Resolution, sample rate and
sensitivity
Accuracy ± (4 ppm + 1 digit) @ 23oC ±5oC
Time base 4.194 MHz quartz crystal
Temp. coefficient 0.1 ppm per oC typical

Resolution and sampling rate specifications

Range Gate time selection Resolution (Hz) Sampling time (sec)
2500MHz

500MHz

10MHz

NOTE: In SLOW Gate Time mode (Gate switch set to SLOW), pressing the RESO key

scrolls the meter through SLOW, SLOW (Select1), and SLOW (Select 2) modes.

Sensitivity specifications

Ch.B: 500MHz range

Ch.C: 10MHz range, Period  50mVrms

Notes on sensitivity: The apparent sensitivity when feeding a signal into Ch.A may vary

considerably, particularly near 1GHz. The meter’s input impedance is a complex impedance,
whereas the output of most signal generators is calibrated for a 50Ω resistive load. This will
result in a terminal voltage different to that expected by the generator, and therefore a
different sensitivity.

105mA DC approx. 2500MHz/500MHz ranges Power consumption

45mA DC approx. for 10MHz & Period ranges

Ch. A: 2500MHz Frequency range
Ch. B: 500MHz

Refer to Sections 2.3 and 2.4 below

5V peak to peak max. for 2500/500MHz range Input overload
250V peak to peak max. for 10MHz & Period range

FAST 1000 0.5

SLOW 100 2.75
SLOW (select 1) 200 1.5
SLOW (select 2) 500 0.75

FAST 100 0.75

SLOW 10 6
SLOW (select 1) 20 5
SLOW (select 2) 50 1.5

FAST 10 0.5

SLOW 1 1.25
SLOW (select 1) 0.2 6
SLOW (select 2) 0.1 11

 100mVrms (50MHz to 75MHz) Ch.A: 2500MHz range
 50mVrms (76MHz to 2500MHz)
 120mVrms (10M to 35MHz)
 50mVrms (36M to 350MHz)
 120mVrms (351M to 450MHz)

381235 Ver. 1.5 3/01