Tuesday, February 9, 2010

SoftRock v6.3 RXTX+Xtall

About 2 weeks ago, I finished building a SoftRock v6.3 RXTX+Xtall SDR transceiver.  I ordered the transceiver and  3 power amp, low pass TX filters, so I can cover 80 meters thru 10 meters.

The 6.3 TXRX is a 1 watt PEP transceiver capable of running whatever frequency bands that you supply PA's for.  The standard kit allows for 16 presettable (with a 4 section DIP switch) frequencies.  Each frequency is tunable over  a span of 96 KHz with the software, with the preset dip switch setting being the center of that tuning range.  All modes are possible, including SSB, AM, NB FM, and all of the digital modes, including Slow Scan Television using outboard software.

Most of my operation so far has been on WSPR on the 40 meter band, however I have operated SSB on 20 and 40 meters, and have worked a couple of countries using an outboard HFPack amplifier at about 15 watts.  The performance is nothing short of remarkable, and have gotten exceptional audio reports while using a VERY cheap computer microphone.

Operating an SDR transceiver requires the use of 2 different sound cards.  I use one card that works as the digital signal processor for the radio and the other to drive the speaker on receive and mic for transmit.  For the radio card, you want the best sound card you can get, with the lowest noise and highest sample rate.  92 khz sample rate cards are available with noise floors in excess of -100 dB, and they are common and inexpensive.  I bought a Soundblaster Audigy card for this purpose, but with many soundblaster internal cards, there is some phase shifting in the card, and I couldnt get a good balance without setting the phase and amplitude all over the place.  I've used an older USB card such as the Soundblaster Live external card and that works pretty well.  The external cards apparently do not suffer from the phase shifting that the internal cards do.

With the bare transceiver with the fixed frequency settings, the only software that is useable with it is a special version of PowerSDR, called;PowerSDR-SR40 and is available at  http://powersdr-sr40.sourceforge.net/.  All other versions do not allow you to transmit if the fixed frequency is enabled.  There is, however an add on module that allows USB control of the Si570 oscillator that allows continuous tuning, which I ordered but have not received yet.

I will write more stories on this radio, and will detail a little more precisely on setting up this radio for use.  It is a fun little rig, and for roughly a $100 investment, you will have yourself a very capable little radio.

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