The grabber is made from a simple SDR kit, the Soft66Lite, a Behringer UCA202 USB sound card and an old P4 desktop. The SDR receiver is SDR# and the FFT processing and display software is PA2OHHs analysis program LOPORAv2. The SDR radio has a crystal frequency of 20.250Mhz with a piece of copper soldered to it, inside a homebrew crystal oven.
Grabber status: Back online!
10 minute grab Stacking: Peak values | Average values
30 minute grab Stacking: Peak values | Average values
00:00 | 00:30 | 01:00 | 01:30 | 02:00 | 02:30 | 03:00 | 03:30 | 04:00 | 04:30 | 05:00 | 05:30 | 06:00 | 06:30 | 07:00 | 07:30
08:00 | 08:30 | 09:00 | 09:30 | 10:00 | 10:30 | 11:00 | 11:30 | 12:00 | 12:30 | 13:00 | 13:30 | 14:00 | 14:30 | 15:00 | 15:30
16:00 | 16:30 | 17:00 | 17:30 | 18:00 | 18:30 | 19:00 | 19:30 | 20:00 | 20:30 | 21:00 | 21:30 | 22:00 | 22:30 | 23:00 | 23:30
The crystal oven was attached to the underside of the PCB. The crystal was folded over, grounded at one end, then a piece of copper was soldered on top. A 50R thermistor and two 100R resistors were glued to the copper. The control circuit is very simple, the 50R thermistor, 220 ohm and 47 ohm resistors form a potential divider across the 5V supply. The 47 ohm resistor raises the voltage across the thermistor so the transistor switches off at a hotter temperature. This turns on and off the 2SC1815 transistor which controls the 12V supply to the heater resistors. With a 100R thermistor and a single heater resistor, the component count could be reduced to four. A small plastic case made from scraps was glued together and placed over the circuit.
The following two photos show the SDR receiver connected up on the workbench and the development setup.
The grabber was installed into a small aluminium case, the same type as the beacon.
The antenna is 1m diameter magnetic loop, near ground level.
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