Bergoz MX-BPM, Руководство пользователя

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The requirements above are very different from the usual specifications of
telecommunication equipment. It was therefore necessary to build a special amplifier with
discrete transistors to cover the 100 MHz to 1 GHz frequency range and reach an
acceptable compromise between conflicting demands.
Local oscillator and frequency converter
An active mixer is used as down converter to the 21.4 MHz intermediate
frequency (if). This is another critical element in the signal chain, where gain compression
is likely to limit the available dynamic range. Thanks to the agc in the preamplifier, the
signal amplitude changes are already reduced at this point.
f
vco
= (N M + A) f
ref
for A < N
M modulus (64) for 64/65 mode
N preset counter (10 bit)
A preset swallow counter (7 bit)
F-key : 17-bit serial word
Fig. 2 Frequency synthesizer
VCO
reference
divider
crystal
oscillator
2 modulus
prescaler
prog.
counter: N
swallow
counter: A
f
ref
F - key
4.433619 MHz
loop filter
phase detector
f
vco
The local oscillator should not contribute any significant amplitude or phase
noise to the processed signals. A frequency synthesizer is used as a source. It consists of
a VCO (voltage controlled oscillator) with programmable divider (5), phase locked to a
reference frequency (fref). A 17-bit serial word from the plug-in F-key module selects the
divider ratio for a specific receiver centre frequency. Spectral purity of the local oscillator
depends on the choice of the reference frequency and the dynamic response of the phase
locked loop (PLL).
IF-amplifier and demodulator
The integrated circuit* used as if-amplifier and demodulator is designed for
television applications. We had to add discrete transistor stages at input and output of the
if-amplifier to match the if-filters and improve the gain compression limits. The if-
bandwidth (Fig. 3) can be tuned from 200 kHz to 2 MHz to suit any particular
application. The bandwidth is large enough to allow a fast step response when switching
from one input channel to the next. Sidebands at the revolution frequency are rejected, to
make the detector see the same kind of signal independently of the accelerator operating
mode: multibunch or single bunch.
___________________________
* LM 1823, National Semiconductor Corporation