Some chips arrived, had not had a lot of time to work on this:
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But placed some stuff, tested the VCO, changed the circuit to put the FIFOs in series..
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Actually there is going to be a 10dB attenuater pad between VCO and that QAM modulator on the right, and 1.5 GHz connections are only a few mm on the PCB (SMD), longer on the chip adaptor.. a lot shorter than the wavelength..
GPS replay from Raspberry Pi, 4 MB IQ per second, recorded from GPS with a GPS mouse connected to a 4000 tuner USB stick. Will 8 K fifo be long enough to cover Linux task switching? If this works I can make a DVB-T modulator too, and send transport stream.
But it is one of many projects... :-)