Bruker DAEDALUS, Service Manual

Page: 45 / 145

Function Description
Daedalus Lock Manual Spectrospin AG 39
Digitalization of the 10 MHz Reference 5.1.2
The digitalization circuit for the 10 MHz Reference is the same as used in other
NMR instruments (e.g. SE-451).
The 10 MHz sinus signal is changed by a regulating DC voltage in the IC80 Gate
into a 10 MHz square wave signal. The regulating signal is taken from the average
value of the symmetrical square wave and is adjusted via R112. The positive feed-
back (R105) stabilises the circuit and retards multiple switching of IC80 on the
flank.
If the 10MHz signal is missing at input J1, the regulating voltage begins to oscillate
between zero and five volts (because of charging at C61).
60 MHz Multiplier for DDS Clock Frequency 5.1.3
Using the different time delays from two gates (Pins 4 and 5 of IC81) a needle im-
pulse (Pin 6) is generated from the digitized 10 MHz square wave signal. Such a
needle impulse contains all multiples of 10 MHz (10, 20, 30 ...MHz). The R107 re-
sistor and the C60 condensor determine the pulse width of the needle impulse and
therefore also its spectral distribution. In reality the needle impulse is somewhat al-
tered by the load.
Following generation a filter selects a frequency of 60 MHz. The operating level is
reached by combining the amplifier MOD3 with an attenuator, consisting of C157,
R117 and R136.
J10 is a coaxial print connector for tests. The two resistors R144 and R145 and a 50
Ohm load function together as a 20dB attenuator.