07-03-2012, 10:15 AM
Hello Al, yes this SDR stuff is new to me, I find the concept interesting, it seems to be attracting a fair bit of interest in amature radio circles. I am now thinking that using just a few valves for the first stage (Aerial in to I & Q out) ie: the direct conversion bit might not be possible as apparently the amplitude and the phase difference of 90 degrees of the VFO needed to feed the two mixers has to be spot on in order to get sufficient audio image rejection down to a good level, I think this might be difficult if the VFO has to tune through a typical amature band spectrum say 200/300Khz. Having said that I am sure that there must be some software out there that can be used as a audio low pass filter in which case I suppose you could build a conventional valve direct conversion receiver and use that software instead of the normal passive or active low pass filter, it would not cure the audio image problem but could help to a certain degree. All very interesting.
As regards the link I posted regarding the basic explanation of SDR I realize now that there are some grammar and other issues with it, but at the time I did not notice them, I was just reading the jucy bits!
Lawrence.
As regards the link I posted regarding the basic explanation of SDR I realize now that there are some grammar and other issues with it, but at the time I did not notice them, I was just reading the jucy bits!
Lawrence.
