Friday, June 29, 2007

Setting Up A Dual SDR-IQ Monitoring Station, Part 3

I think my dual IQs are up and running now, but not without problems!
I installed Spectravue on two different folders on my new Fujitsu-Siemens. Fired up the first problems but when I increased the demod span from 150 to 190 kHz audio was distorted. I fired up IQ no 2 and distortion was even worse! Was it the sound board? I had a Creative USB board around so I installed it. No cigar.

I tried to record an RF file. I got the first session of Spectravue to record, but not the other. So what was it? Vista, the OS, known for its compatibility problems? Finally I emailed Pieter at RF Space, who had managed to run four sessions of Spectravue simultaneously. Surely, the PC wasn't too weak?

His initial response wasn't too optimistic: "I really don't know what to tell you..." but then he asked if both IQ USB contacts were placed at the same USB controller, and if so, try to move one of them to another controller. Well, both USB contacts were placed at the same controller at the back of the PC, and I moved one of them to a contact up front.

And as if by magic, the problem was gone! I can now demodulate, and record RF from both IQs without problems, at a full 190 kHz.

Now, there is a problem. The beautiful 19" widescreen LCD does emit RFI on a small portion of MW, from 629 to 642 kHz. I can turn the display off and the problem (measured to -105 to -120 dBm) is gone. I adjusted the brightness which reduced the problem somewhat (and it was much too bright to begin with). You can see the RFI on the picture, to the left of the centered signal at 657 kHz on the Spectravue running to the right.

Now remains to see if the sessions run stable over a long period of time. The combined CPU strain is rarely higher than 50% so there should be plenty of overhead for running other programs like a browser or a word processor.

One more word on the PC: The Scaleo J is a very quiet PC and that is quite important to me. I don't like high-speed fans running all the time.

Looks promising, despite some deep worries at the beginning.

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