> John, > It's interesting that there is almost no evidence of the 500 MHz ADC > clock, > except perhaps the 2000 MHz tone. I guess that means the ADC clock > transmission lines are well terminated and not radiating. Most of the > lines > look like they are related to the PPC (multiples of 33 MHz) and the 100 > MHz > system clock.
You're right that most of this is due to the PPC and ancillary circuits. I expect that it's because the FPGA is not loaded. The line from the clock to the ADCs is very short. I am going to test it again later with the FPGA running a spectrometer bof, and all the xaui cables connected and passing data around. For now, this is enough to tell me that we need to be thinking ahead to packaging VEGAS. John > Glenn > > On Tue, Sep 6, 2011 at 1:14 PM, John Ford <[email protected]> wrote: > >> Hi all. >> >> We tested a ROACH and and 2 ADC boards (3 GS/s boards) in our anechoic >> chamber to get a feel for the emissions to expect from the new >> spectrometer being designed. The ADC clock was running at 500 MHz. >> >> The results of the test are attached. In summary, to use these at our >> site, we will have to have a supplementary shielded enclosure in >> addition >> to our shielded equipment room. >> >> Thanks to Carla Beaudet at NRAO for the testing. >> >> (If anyone has anything they'd like us to test in the chamber, let me >> know.) >> >> John >
