The most useless extension for the SoftRock

Publié: 17 janvier 2009 dans SDR

… adding a frequency meter for a Software Define Radio is probably the most useless thing to do… But I’m one of those hams who need to “read” the frequency on a front panel from time to time. That’s a pure cosmetic add-in. It only tells you that the Si570 is doing his job and that the software is sending the good commands (and probably adding some noise… l’ll check that later)

Well…the less expensive meter I found is made by N3ZI (www.pongrance.com). Depending on what you’re looking for, the price of your instrument will cost you between ten to twenty-five bucks. For 25 $, you get a clean pair of pcb and components (and mostly one PIC microcontroler and a prescaller). For Softrock use, the IF should be set to Zero, the prescaller hard wired to the “divide by 8” input, and the divide factor by 8 or 80, depending on the precision of the measure you need. Those tuning are fully software controled… it’s definitely for nobrainers.

The DIL switch located on left hand side was used to play with the prescaler. But flying wires between the prescaler and the switch was too much radiating.

The signal is picked up on one of the test point marked “QSE” (have a look at the silkscreen of the SR board).

After some harware adjustment (I still hate that !), the Softrock’s working frequency is displayed. When no computer is connected, the Si570 falls back to it’s default starting frequency (56 MHz). As the signal is taken after the quadrature mixer, the exact working frequency (56/4) is displayed.

As many hams seems to have problems connecting a UBW to the softrock, the next story will be dedicated to the conception and wirering of a TTL/I2C discrete interface, and the installation of the WB6DHW 18F2550 USB controler. Cheerio.

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