Mike, I think you're right that SDRs that digitize at a zero IF (like the KX3) need I and Q channels to distinguish the AF sidebands. That is, if the radio mixes 7030.4 kHz down to a sidetone of 0.4 kHz, it also catches signals at 7029.6 kHz.
And I think that SDRs that digitize at a non-zero and 'properly intermediate' IF (that is, neither 0 nor the VFO frequency) also need I and Q channels to distinguish the IF 'sidebands'. That is, if the radio mixes 7030 kHz down to an IF of 455 kHz, it also catches signals at 6120 kHz. But I think that SDRs that digitize at the VFO frequency itself (I believe this is generally called "direct sampling" on RX and "direct digital synthesis" on TX?) can get away with a single channel, since there's no mixer to cause the "you mix A and B and get both A + B and A - B even though you only wanted one of them" problem. Does this match your understanding? Thanks, Julie On Wed, Jun 22, 2022 at 2:04 PM Mike Markowski <[email protected]> wrote: > Jerome, > > This answer is for generic SDRs, since I don't have a KX3. > > An SDR always must use both I and Q, even for CW. I and Q are two > streams of samples of the same signal. One of many advantages to i/q > sampling is the ADC's can run slower (cheaper). In the extreme and > ignoring the intrusion of real life components on sampling, a 10 kHz > wide signal could be sampled with I and Q ADCs running at 10 kHz. > Nyquist is satisfied because you have 2 streams, or 20 kHz sampling in > this example. Aliasing prevents you from using just I in that case. > > The fact that Q is 90 deg from I, means we can plot them on axes 90 deg > apart. That allows re-appropriating the entire field of complex > mathematics to work with the samples. I and Q are both physical - > trying to avoid the word 'real'! - streams of samples, but I can be > called real and Q can be called imaginary. Using Euler's Formula, they > can be bundled into a concise exp(j phi) formulation to work with. > > I/Q imbalance is always a concern. Maybe others can quantify it better > than me saying smaller is better. :-) > > 73 es GL! > Mike ab3ap > > On 6/21/22 11:08 PM, JEROME SODUS wrote: > > Hello, > > > > Although I have asked some of these questions on another forum, here I > have expanded on them a bit. > > > > When the KX3 transmits a CW-signal, are both I and Q used? > > If so, why would that be necessary? > > (My guess is only the I is needed.) > > > > Same questions too for a SSB-signal. > > > > But, for any digital transmission like RTTY, FT8, or Olivia, wouldn't > both I and Q would be active? > > > > The LO is used for the "In Phase" and is delayed by 90 degrees for the > "Quadrature"; how is that delay done? > > How much can the delay deviate from 90 degrees and still be useful? > > > > My reason for asking is that I'm to give a talk to the Radio Club in > August about how a KX3 works and want to mention these details. > > > > TIA for any replies. > > 73 jerry km3k....KX3#6088 > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[email protected] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: http://www.qsl.net/donate.html > > Message delivered to [email protected] > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
