Read first! I am no longer building this transceiver. Please check other interesting projects from Farhan on the discussion group, like HF-1 Transceiver, the replacement of the Minima and some cool RF jigs, Specan and Sweeperino. Also, since I’ve lost from both server and my drive the Eagle files of the PCBs, they will be no more available. Minima has become discontinued, check the group for more details. I will still keep the pdf files here for download for anyone still interested in hacking the rig.
The Minima main board is starting to take good shape. These days I have soldered the crystals, test the BFO and added some other components to the PCB.
My 5$ – 100 pcs pack of crystals finally arrived from China, so I proceeded to sort 8 of them. For measuring I have used the BFO schematic from the Minima, built on the small test PCB, and an ordinary PIC frequency counter. Since the counter is not super calibrated I did some relative measurements, just to select eight pieces with the most appropriate values.
Because of the laziness, I have only tested 50 pcs, but enough to choice the right ones. Very helpfully was using an Excel spreadsheet. I’ve marked the crystals with an unique number, and write down the frequency value associated with that number in Excel, and then auto-sorted. From all the list, the best 8 crystals interval was this one below, with 90 Hz difference between the 1st and 8th in order.
When adjusting the BFO, I have considered 19.995.500 as the center frequency of the crystal filter, so the two sides frequencies adjusted by the trim caps are 19.994 and 19.997.
The Si570 finally arrived from SDR-Kits. Actually the second package. The first one was lost somewhere by the post service. They were very kind to send a replacement, just paying only the shipping fees. By this way, I would like to thank to them for this gesture.
More or less, I have collected all the parts for the Minima. Hope to put it to work very soon. Still to wind the coils, program the Arduino and wiring between boards and switches-pots.