Modifying the Softrock Lite, add Si570, plug-in BPF

A few low-res pictures just to show how someone might modify a Softrock. See my note at the bottom for a more sensible approach.

This is a single frequency 6.2 Lite. None of the crystal oscillator components are installed.

A 3V3 regulator is fitted underneath using spare tracks. Some were cut to isolate from the rest of the board.

A Si570 is mounted "Dead bug" fashion, pull-ups for the control pins are SM resistors under the board. Connections go to the 4 pin socket. The output is connected to the divider in a similar manner as in the Ensemble. (Through C3 with the input pin biased to 2V5)

A small board carries the USB AVR and plugs into the 4 pin socket.

The USB is connected to this board.

My reason for doing this was to make a receiver that could be set to any single frequency by using CFGSR to store that frequency in the AVR. This early Softrock has a /8 choice so with a suitable BPF can go down to about 400KHz.

Most of this could be avoided by using a Si570 kit. https://sdr-kits.net/index.php?route=web/pages&page_id=53_53 is almost a Softrock equivalent. I recommend changing the AVR to the ATTiny85 with Fred's superior modified firmware. http://thepartsplace.k5nwa.com/index.php?route=product/product&product_id=53

Such a kit can be fairly simply added to a single frequency Softrock to cover the whole of its designed band. It would receive outside this band but for best results the BPF may benefit from modification.

This may also be used for a RXTX, a 6.3, or earlier. They already have COM port PTT but most likely the USB TX could be used.

Parallel port control has been used, a possible adaptor https://www-user.tu-chemnitz.de/~heha/basteln/PC/USB2LPT/index.en.htm

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