The DSP Receiver KWZ 50
The Concept
Overview
The DSP-Receiver KWZ-50 is like its predecessor a receiver for the frequency range
10 kHz to 52 MHz using digital signal processing.
It was predicted for a long time that the analog/digital converter moves closer to the
antenna. This is the case too in the KWZ-50. The first intermediate frequency is 75 MHz
as before. From there the signal is converted to 30 kHz using quadrature mixers. This second
intermediate frequency is fed to the A/D-converters. Then follows the DSP-unit, which is
equipped with a high performance DSP (32 bits).
The Controls
The controls of the KWZ-50 are much more comfortable than the controls of the predecessor,
which intentionally were designed thrifty. The display is a colour display (quarter VGA) with
a resolution of 320 x 240 pixels. On either side of the display are 4 programmable keys. So
the current function of the key can be shown on the display. Besides the main encoder for the
frequency tuning there are three more encoders with smaller resolution. One is dedicated for
the volume control while the other two can be programmed for other functions. Of course there
too is a key pad with the numerical block and other keys for the menue control and also for
dedicated functions.
The Circuitry
The analog part of the set is a double conversion superhet with the first IF of 75 MHz and
the second IF of 30 kHz. In front of the first mixer the signal is passed though a low pass
filter, a switchable high pass filter and an amplifier/attenuator stage.
The conversion from the first IF to the second IF is performed using quadrature mixers which
secures a high mirror frequency attenuation. The mixers are followed by two A/D-converters
with a dynamic range of 120 dB. From the A/D-converters the signal is passed to the DSP.
It is a 32-bit DSP from Analog Devices. So there is an almost unlimited dynamic range available
for the signal processing. In the DSP the selection and demodulation of the signal is performed
as well as the other functions like notch filter, noise reduction, squelch and others.
DRM: The intended hardware-solution could not be realized because there is no
such module on the market. The DRM reception is possible with an external demodulator.
The KWZ-50 has an if-output with the center frequency of 12 KHz (line-out).
We have decided to use a conventional power supply with a transformer, rectifier and
capacitor fiklter, The voltage is 13.6 Vdc. From this voltage all needed voltages
are generated using switchinh voltage converters. So the set can also be run with
12 to 15 Vdc.
Back