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Tuesday 9 March 2010

Another SDR CDARC Rally question...

> Sent: Tuesday, March 09, 2010 10:39 AM
> Subject: SDR at CDARC Rally
> Just wondering if you could let me know which model
> Softrock kit it was that you had at the G-QRP stand at the
> CDARC rally at Wood
> Green this past weekend?
> best regards
> Lawrence M0LCM


The setup was mine....

KB9YIG Softrock V9.0 Lite with manual 80/40m LPF with V1.4 (V.OLD!) usb control software for the Si570 CMOS DDS. Would have to check but I think the op amps following the LO dividers were from the old design too not the current ones. (Just checked they are TLV2462CD not LT6231CS8)

The rig was a kit built into a simple Ali enclosure (Maplin) with telfon isolated RF-BNC (Maplin) and isolated AF phono sockets (Maplin) and power was from a 1.3AH 12V battery (Maplin) note no mains derived DC used.

Audio was double isolated using back to back 600 ohm isolation transformers with good audio response 100Hz to 25kHz (only way to find out which ones work is to test them!). As stereo means there were 4 of these transformers in the isolation interface.

Sound card is external USB 24 bit 96kHz sample rate. The sound card A/D bit number IS CRITICAL for decent SDR performance also you MUST have REAL stereo input into dual A/D channels (only way to check is to trace the audio in on the M/B and locate the chipset and do some data sheet look ups. It really does make a difference. Normal PC cards even the fancy games ones are still only 16 bit and 48Khz and MONO input.

All laptop to external connectors had common mode chokes with at least 10 turns through type -61 or -77 ferrite rings.

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