S-Band spectrometer based on Callisto

Below 1 GHz local interference (rfi) is too high to get acceptable data quality. Therefore I decided to go higher in frequency into S-band. A cheap WiFi antenna is pointing to the meridian position of the sun and the rf-signal is down-converted by a heterodyne converter (eBay) into the base band of Callisto. With this configuration it should even be possible to measure quiet sun flux...

Input reflection coefficient Callisto

s11 over the whole frequency range of Callisto is always < 10dB. Philips specifications guarantees 8dB. So this instrument is o.k. in terms of input reflection.

Basic schematic Callisto

Callisto is a double heterodyne receiver with two IF, first at 37.7 MHz and 2nd at 10.7 MHz.
RF- and IF-gain are controlled by a PWM-signal via ATmega16. Detector is a logarithmic AD8307.
Tuner is Philips CD1316x, where x denotes to different versions.
Callisto is connected via RS232 (115 kbit 8N1) to a standard PC running on Windows 98, 2000, XP or 7. Third party software for Linux can be found on my instrument website.