BackThe KWZ 30 is a double conversion receiver with an added DSP. The input signal reaches the first mixer through a low-pass filter with 30 MHz cutoff frequency. As this mixer has a very high intercept value IP3 of 30 dBm (at 20 KHz frequency difference), narrow-band preselection and an attenuation are not necessary. The first IF signal is then processed by a crystal filter (75 MHz +- 7.5 KHz) and an if-amplifier and is converted by the second mixer into the second IF of 456 KHz. From there the signal is amplified and fed to the A/D converter at a bandwidth of +- 7.5 KHz.
Further processing, selection and demodulation after digitizing takes place at the IF of 0 (Zero). Therefore the KWZ 30 could be called a triple conversion receiver. After the DSP the signal is fed to a D/A converter, the audio-amplifier and the speaker (or a decoder).
The DSP is the major improvement over traditional receivers. It is here where selection and demodulation of the signal are done exclusively.
The DSP module consists of:
After digitizing the signal is transformed to a center frequency of 0 (Zero) in two channels (I- and Q-signals). Now the desired signal is filtered according to the selected filter bandwidth and is fed to the demodulator. The signal is then converted back to analogue and fed to the audio-amplifier. The DSP also keeps the output level constant. The very high accuracy allows for the field strength (S-meter) to be displayed in dBm!
In addition the following functions have been integrated into the DSP module:
The oscillator system generates all necessary frequencies. These are all derived from a single temperature-compensated quarz oscillator. The oscillator system uses DDS technology (direct digital synthesis), making it extremely low-noise. Tuning resolution is 1 Hz and the accuracy better than 20 Hz within the 0 - 30C temperature range. The VFO frequency is adjustable from 75 to 105 MHz. The frequency step can be selected from 1 Hz to 50 kHz per tuning-pulse. The tuning knob can be adjusted to generate between 2 and 400 pulses per revolution.
The computer accepts the operator input and controls the DDS-oscillator, DSP module and LC Display accordingly. Inputs are made with the tuning knob and / or keybord. All parameters, e.g. tuning resolution, frequency step and AGC time constants can be selected by the operator. It is possible to switch to a second VFO at any time. 250 frequencies can be stored in the station memory along with the respective mode, bandwidth etc. An RS-232 port is located on the back panel allowing PC-controlled operation.
The display is a backlit LCD showing all relevant parameters during reception. During menu selection the dispay resembles a computer screen showing the menues and sub menues.