[Elecraft] I/Q details for the KX3.

[Mike Markowski]

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:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to mike.ab3ap at gmail.com