QRP Labs QCX-mini, Assembly Instructions Manual

Page: 129 / 133

17m band
3dB bandwidth: 1,352kHz
Insertion loss: 2.77dB at 18.120MHz center
Tuning range: 12.64MHz to 35.0MHz
6.8 Quadrature Sampling Detector bandwidth
The following chart shows the attenuation naturally provided by the Quadrature Sampling
Detector from -20kHz to +20kHz from the Local Oscillator frequency. The narrow
characteristic of this circuit is an advantage because it effectively adds an additional narrow
RF bandpass filter to the receiver, preventing strong nearby signals from reaching the audio
amplifier stages. This improves intermodulation performance.
The circuit parameters are optimized for CW operation in this transceiver. A constructor
wishing to use the I-Q outputs from IC5 to feed a computer SDR, would wish to flatten this
response. To do this, reduce the values of the four 470nF capacitors C43 to C46.
QCX-mini assembly Rev 1.05_Fr
129