[hpsdr] "Infinite Precision?"

[Murray Lang]

What about the situation where QSE is the only "mixing" stage and I/Q is 
from a sound card? Where does frequency response come into it? You've only 
talked about word size. You seem to be saying that phase is a DC component 
of I/Q.

Murray
VK6HL

At 01:08 PM 6/09/2006, Robert McGwier wrote:


>Murray:
>
>You are getting there.  Keep asking questions since you are not the only 
>person here who needs these questions answered.
>
>You might as well have continuous phase since the difference between you 
>and continuous phase is so small as to not be worth mentioning.
>
>Let P1, P2, ..., Pn   be the phase offset of the LO's or clocks in the N 
>stages of a receive system
>
>The phases are COMPLETELY commutative.
>
>(P1+ phi) + P2 + P3 + ... + Pn   =
>P1 + P2 + P3 + ...+ (Pn + phi)
>
>Where P1 is the first LO and Pn is the last "LO" in the system.   Since Pn 
>will be the software oscillator in your SDR system,  the precision for phi 
>is determined by the precision of a floating point number.   Since this is 
>2^23 bits  we have 138 dB of range in an IEEE float.     Since ALL of the 
>oscillators in your coherent phasing system are derived from the SAME 
>source for each of the antennas,   the RELATIVE phase offset,  which will 
>be determined by the software LO has this 138 dynamic range.  Your phased 
>array can't possibly have enough elements in it to use all of that 
>precision since they half power beam width of any real antenna system is 
>going to be about 12 orders of magnitude worse than you could possibly use.
>
>Bob
>
>
>
>
>Murray Lang wrote:
>>
>>***** High Performance Software Defined Radio Discussion List *****
>>
>>Thanks Robert,
>>
>>I need to go away and try to get my head around it some more. I need to
>>understand the relationship between the sampling resolution of I/Q and the
>>
>>resolution (ie step size) of phase adjustments that it can apply to RF.
>>It's not going to be continuous. I'm starting to work on the math, but I
>>have a way to go.
>>
>>Cheers
>>Murray
>>VK6HL
>>
>
>
>
>--
>AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
>NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
>"You see, wire telegraph is a kind of a very, very long cat.
>
>You pull his tail in New York and his head is meowing in Los
>Angeles. Do you understand this? And radio operates exactly
>the same way: you send signals here, they receive them there.
>The only difference is that there is no cat." - Einstein

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