Minority report?
Things work out great. As mentioned in previous postings, the idea is to send IQ data (for example recorded with RTL_SDR) from a Raspberry Pi SDcard to a dual DAC AD9761 into a AD8346 quadrature modulator.
8kB FIFO Raspberry Pi -> CY7C433-25PC_FIFO -> AD9761_DAC -> AD8346_QAM_MODULATOR -> RF out | ^ ^
default) to reduce systems calls,
If you can keep up the data flowing without breaks, you won't need any I/Q flags - just have the channels alternating IQIQIQIQ.
You can't really tell whether the sequence starts with I or Q, but at most you'll have a constant 90deg phase shift, which really does not matter unless you're targeting carrier sync with some other part.
I still remember when I got the first samples for AD9857 and was trying to find out a way to tell AD9857 which sample is I and which is Q and then having the lamp light up!
-- Mikko OH2HVJ
On a sunny day (Wed, 24 Apr 2013 09:01:59 +0300) it happened mikko wrote in :
default) to reduce systems calls,
Yes. I deduced that at some point from the datasheet 'state machine' story.
Absolutely true, but may get problematic once you have more than one of these working together in some way.
Na yaj, the bit is free, Raspberry has plenty of I/O pins, and the FIFO chips are 9 bits, so I just wired that to bit 9 and that to the 'select' input of the DAC.
Already with testing, with the scope on the DAC output, I can tell it has I and Q the right way around :-) What I do not like about that dual DAC is that if I listen to these generated 'audio' tones, I can hear al sort of aliasing, scope shows it too. I think this is because of that internal multi stage filtering. Already I decided if that is going to give problems, I have 2 old video DACs as standby. Those are clean...
Lot more experimenting to do... Thanks for the feedback.
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