[hpsdr] "Infinite Precision?"

[Murray Lang]

At 09:41 AM 7/09/2006, Murray Lang wrote:
>***** High Performance Software Defined Radio Discussion List *****
>
>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.

Sorry Bob, I realise that I haven't done justice to what you've posted. I 
can see that the commutative nature of mixing helps but I'm having trouble 
relating that to the situation I've identified above. The only oscillator 
is the 4xoutput carrier and it's being modulated by a sound card.

Murray
VK6HL


>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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