Circuit Description
3.1 Block Diagram Description - 1599-10 (Figure 3.1) - Broadband noise is generated by noise diode CR1
followed by various amplifiers (U1, U3, U6, U8 with 21 dB gain; U15 with 13 dB Gain), a 200 MHz lowpass filter
(L16, C58, C62), 70 MHz bandpass filters (10 MHz consists of L3 - L6 and associated parts; 40 MHz consists of
L18 - L 21 and associated parts), voltage controlled attenuators (U3, U7, U14), and a noise termination switch (U5)
before being summed with the external signal by a resistive summing network (R43, R44, R38). The input signal
goes through a variable attenuator (R42) for precise unity gain to the output, signal termination switch (U11), and
buffer amplifier U13 before being summed with the noise by resistive summing network, R43, R44, R38. The
combined signal plus noise goes to output amplifier U9 and output monitor amplifier U10. Controller U23 and
associated circuitry provide attenuation commands to the attenuator D/A U17 and the noise diode bias D/A U16
which provides 0.1 dB steps and slight temperature compensation as needed to maintain the noise power accuracy
over temperature as specified.
Commands for the D/A’s, noise termination switch, signal termination switch, and test oscillator switches are
provided from microprocessor U23 which receives serial RS232C commands from an external (not supplied) PC
via RS232C receiver IC, U21. Microprocessor U23 can send serial RS232C commands to an external PC via
RS232C transmitter IC, U38. Noise level (either continuous or preset noise levels), test carrier on/off, and
termination of carrier or noise can be remotely commanded from an external (not supplied) PC using a simple
DOS program.
Microprocessor U23 uses its internal oscillator controlled by the 3.6864 MHz crystal Y2. U19 is a watch dog
timer for microprocessor U23. IC’s U30, U31, U32, U27, U28, U29 provide multiplexing and strobing of displays
DS2, DS3, DS4.
3.2 Controller Operation for 1599-10 Noise Source
3.2.1 General - The controller consists of a microprocessor and associated circuitry which receives inputs from:
a) the front panel noise level set switches (SW2, SW3),
b) the front panel terminate noise/carrier switch (SW1),
c) the front panel test carrier switch (SW4),
d) the on card display mode jumper (JP7),
e) the on card preset level programming decimal switch (SW6),
f) the on card preset level programming “push to program” switch (SW5),
g) the on card local / remote control mode jumper (JP9), and
h) the on temperature detector IC (U35)
The controller provides command signals to the:
a) noise level D/A’s (U16, U17),
b) carrier, noise terminating switches (U5, U11),
c) test carrier enable switch (Q2), and
d) the front panel noise level display (DS2, DS3, DS4).
In addition, when in the remote control mode, the microprocessor U23 accepts a serial data stream which is
generated by a simple DOS program (by an external, not provided, PC) that selects the noise level and the output
level. Serial data is received via RS232C receiver U4 and sent via RS232C transmitter U38. The following
provides additional detail.
1599-10 Manual, Rev. A
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01/07/10
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