2012-11-18 · in Tech Notes · 243 words

SoftRock RX in a box

This is a SoftRock RX Lite + USB Xtall V9.0 with an HF BPF board fitted. It's a software-defined shortwave radio receiver with continuous coverage from approximately 1 MHz to 30 MHz. I normally use it with my softrig SDR frontend.

I built it in 2010 from one of Tony Parks' excellent kits, and drilled a plastic food container to hold it. In 2012, I decided it really deserved a proper shielded box.

I took the opportunity to add a buffered output from the local oscillator at the same time, so I could use it as a software-controlled signal generator. The extra board on the left is a 74HC-series logic chip (the first one that came to hand!) wired as a buffer; the input is taken from one of the LO test points on the SoftRock board.

The switch controls the SoftRock's muting function; the power indicator is a bicolour LED, wired to light up red when the SoftRock is muted. It uses a common resistor for both colours; I found that by selecting an appropriate value, I could get the green LED to go out when the red LED comes on, owing to their different forward voltages.

At present, the LO output is a 5V square wave. A potential future enhancement would be to feed the output "backwards" through the BPF when the SoftRock is muted, giving a low-level sine wave output on the antenna socket; this would be useful for antenna tuning.