> > Janne and everyone, > > Probably you already know this, but it can be of interest to others. > Some audio audio cards have chips that skew their output channels (i.e. > one channel is delayed 1 sample with respect to the other). Some > software (i.e. kg0sdr, Rocky) have provisions for correcting this > "feature", since without this correction you can't null the image. So, > if anybody is not able to null the image, try this. > > -- > 73 de Ignacio, EB4APL >
Hi Ignacio! Thanks for the reply! I installed and tested the Rocky and it started to do the automatic phase and gain calibration immediately when I delayed the right channel 1-unit, interesting! Also, before you answered I noticed that Winrad does propably the same function when clicking the "One sample delay" in "Channel Skew adjustment" -tab. I was able to have about -20db to -30db image rejection when the phase adjustment was full right. You can see a screenshot of that: http://www.saunalahti.fi/johku76/pic/sdr.jpg It kept goin' better when I adjusted the phase, until it came to the end - 6.837. It would be like to know how much this value is degrees. Now, giving a second though, this might also be a pure hardware issue. I mean, the IQ LO I made is put together in 15 minutes. Just 74HC04, 74AC74, 14.418 MHz Crystal and few passive components. I can measure the output with my oscilloscope and see that the signals have approx. 90 degree relation. But what if they have 85 degree relation and the value 6.837 isn't enough in phase? And there seems also be the problem that my soundcard delays the other channel, uhhh. 73 de Janne, OH1GTF
