Wednesday, January 6, 2010

SDR for QRSS

Finally I started building the SoftRock lite 80. This will be serving as a grabber receiver for the upper QRSS frequency (3599900Hz) as well as the color burst frequency (3579545Hz).
In order to allow for those frequencies, I will drop in a 14.285MHz crystal, which I ordered from Rich some time ago. This will result in a center frequency of 3571250Hz, not too far off 3.6MHz and not too close to the color burst frequency either. This receiver, assuming a sample rate of 96k, will be having a range of about 3.523MHz to 3.619MHz.
The original SoftRock lite kit comes with a 20m qrp crystal (14.060MHz), which would allow for the low QRSS range at 3500800Hz and also essentially covers the 80m CW range to about 3.563MHz.
If you think, this is something I want to build myself, yep, it is doable, and it is cheap (see my links). However, this kit involves some SMD soldering, which not everyone is confident doing.

There is an alternative however. Check out my earlier postings when I was writing about the "box73" SDR kit aka SDR Einsteiger-Kit. This kit is also not expensive at all, and it does not involve any SMD parts. Additionally, box73.de offers a hardware kit for the SDR kit, which provides you with an encasing, connectors and a cable to connect the receiver with a soundcard. The "downside"of this kit is, that it employ a canned oscillator of either 14.000MHz or 14.318MHz. The second would be suitable for the upper QRSS frequency, however, the color burst frequency will zero beat. Zero beat will also be the problem with the 14.000MHz version, maybe it will still be suitable for 800Hz, but, this is very close to the LO. I will try this, I ordered and built the 14.000MHz version. One also could imagine to build a clock oscillator with some gates and a crystal, possibly making it switchable....

BTW, most publications speak about a range of +/- 24kHz for such a receiver. This is since a sampling rate of 48k is assumed. With the built in soundcards of the Asus EeeTOP and the MSI Wind NetTop 96k samples are no problem and a bandwidth of nearly +/- 48k about the center frequency can be received.

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