Michael Blake wrote: > > While it may be operator error, on my part, I am not able to balance the > image signal with the Soundcard Skew Calibration routine. The best I > can get is about a 25dB null of the image signal. The gain settin seems > to have zero effect and the phase adjustment has a very small null at > 0.1 degrees positive. 20 dB is about the worst balance I can get at any > setting so I am only seeing about 5 dB of image rejection when adjusted > as well as I can adjust it. > Mike,
it's not an operator error. The problem is that, when I wrote that routine, I had imagined that the amplitude and phase unbalances would be very small, so I gave a small adjustment range to those controls. Tests done with my hardware (a QSD made with a couple of ADG704 from Analog Devices and a phase shifter done with a 74HC74) confirmed that my hypothesis, as in effect my hardware was already well balanced in itself, needing just a small correction in software. Softrock V5 has a phase delaying circuit composed of a fixed RC network, so it is greatly dependent from the tolerances of the components, and even if they were perfect, an exact 90 degrees phase shift is obtained at one single frequency only. All this means that the adjustment range of my software is not enough to cover the possible unbalances of that hardware... I have received yesterday my Softrock V5 kit and, as time permits, I will build it and test it with SDRadio, so to see which is a good adjustment range for this hardware. 73 Alberto I2PHD ------------------------ Yahoo! Groups Sponsor --------------------~--> 1.2 million kids a year are victims of human trafficking. Stop slavery. http://us.click.yahoo.com/WpTY2A/izNLAA/yQLSAA/ELTolB/TM --------------------------------------------------------------------~-> Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/soft_radio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
