Rocky SDR software
Power SDR software

In the Benelux QRP Nieuwsbrief, Douwe PA0DKO (SK) write some articles about his experiments with Software Defined Radio (SDR). A very interesting part of our hobby because you can use your PC to listen to the amateur bands. You only have to built a SDR front-end and look for some (good) software on the internet. You also should use a very good soundcard, but that is not conditional for starting listening to SDR.

I start building the front-end, described by Douwe, with a FST3253 and 2 LT1028 ultra-low noise opamps. For the Local Oscillator I can switch between an x-tal oscillator with divider (74AC74) or my I/Q DDS Vfo. The both DDS-vfo sinus signals are converted to square wave signals by 2 high-speed comparators (LT1719)

In the same enclosure I build a tunable pre-selector separated in two ranges: 160-30 meters and 30-10 meters.

For SDR software, I am using different programs. See the links on top of this page.

SDR front-end and Tunable pre-selector

SDR front-end

I did some experiments with the software from Flex-Radio, PowerSDR. I like this software because it has a very accurate signal strength meter which is very easy to adjust. I did some measurements with the soundcard on my motherboard (AC97) and with a SoundBlaster Audigy SE card. I put the results in a table (all in dBm).

Card	MDS	MDS + QSD	Input for 0 dBFS	Dyn. range	IP3	Calibrate
AC97 (intern)	-106	-96.7	-4.1	92.6		-50 dBm
SB Audigy SE	-94.7	-89.5	-3.9	85.6		-50 dBm
SB Audigy 4