EG&G ORTEC 427 Інструкція з експлуатації - Сторінка 11

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3-2

200190

RG-62/U

RG-63/U

100 ohm BNC

TERMINATOR

RG-62/U

RG-63/U

100 ohm BNC

TERMINATOR

ANALYZER

-IN

—

GATE SIGNAL FROM

COINCIDENCE OF

CROSSOVER DERIVED

PULSE.

Z|f^ > 1000 ohm

FIGURE 1.

BLOCK DIAGRAM

OF A SYSTEM

USING PROPER CABLES AND TERMINATORS.

or as narrow as 300 to 400 nanoseconds.

The connecting coaxial cable should be terminated in its characteristic impedance

at the input connector when cable lengths exceed approximately 10 feet (see Fig. 1).

The input impedance of the 427 is approximately 1100 ohms. It is recommended that

RG-62/U or RG-63/U coaxial cable be used because of their relatively high impedance

of 93 and 125 ohms, respectively.

If long cables having impedances less than 93 ohms must be used, care must be taken

to ensure that the driving source can drive and terminate the cable. For example,

when driving from an ORTEC linear output with on output impedance of less than

10 ohms, a 50-ohm series resistor should be used between the driving source and the

coaxial cable (see Fig. 2). This makes the output impedance of the amplifier equal

to the characteristic impedance of the coaxial cable; therefore, it is not necessary

to terminate the cable at the input of the 427. However, if the cable is terminated

at the input connector, the signal at the 427 input wil l be one-half the output signal

of the driving source due to the series resistor. The above method of series termination

is recommended for ORTEC linear output circuits when it is necessary to drive a 50-ohm

load at high count rates. This modification can be made on the 427 by removing the

cover plate and replacing the short piece of wire between R and S on the circuit

board with a 50-ohm resistor.

GATE SIGNAL FROM

COINCIDENCE OF

CROSSOVER

DERIVED

PULSE.

RG-58/U

410

50 ohm

427

: 50 ;

ohm

ANALYZER

OXTBC

200191

Z||^ > 1000 ohm

FIGURt 2.

BLOCK DIAGRAM OF A SYSTEM WHEN LONG 50 ohm CABLES MUST BE USED.