Re: [casper] ROACH and ADC RFI tests
Hi All, I don't have our own results in a handy packaged format, but this correlates well with what we saw. If the 533 MHz is fundamental, it is pure PowerPC - the clock is generated on chip from a lower frequency reference. Regards, Francois On Tue, Sep 6, 2011 at 10:29 PM, John Ford jf...@nrao.edu wrote: 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 jf...@nrao.edu 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 -- Francois Kapp Sub-system Manager Digital Back End meerKAT SKA South Africa Third Floor The Park Park Road (off Alexandra Road) Pinelands 7405 Western Cape South Africa Latitude: -33.94329 (South); Longitude: 18.48945 (East). (p) +27 (0)21 506 7300 (p) +27 (0)21 506 7360 (direct) (f) +27 (0)21 506 7375 (m) +27 (0)82 787 8407
Re: [casper] ROACH and ADC RFI tests
Hi, John, That's very interesting. How does this compare with a laptop or other PC? Why was it tested with the lid off? Is that how it will be deployed? Thanks, Dave On Sep 6, 2011, at 1:14 PM, John Ford 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.) JohnRoachBoardsAnechoicChamberRFITestReport.pdf
Re: [casper] ROACH and ADC RFI tests
Hi, John, That's very interesting. How does this compare with a laptop or other PC? Why was it tested with the lid off? Is that how it will be deployed? Laptops and other PCs are a different kettle of fish altogether. They have a wide range of emissions, and most of them have emission about 40 dB above the ITU limits at the distance of the lab here. It was tested with the lid off because that's how it was given to the tester. The standard enclosure is not in any way RFI tight, and would likely have had no effect on the emissions, unless we sealed it up with copper tape. We plan to package them better than they currently are packaged, for sure, likely either packaging them individually in the SA MeerKAT custom enclosure, or in a common shielded rack. John Thanks, Dave On Sep 6, 2011, at 1:14 PM, John Ford 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.) JohnRoachBoardsAnechoicChamberRFITestReport.pdf
Re: [casper] ROACH and ADC RFI tests
Thanks, John! On Sep 6, 2011, at 1:47 PM, John Ford wrote: Hi, John, That's very interesting. How does this compare with a laptop or other PC? Why was it tested with the lid off? Is that how it will be deployed? Laptops and other PCs are a different kettle of fish altogether. They have a wide range of emissions, and most of them have emission about 40 dB above the ITU limits at the distance of the lab here. This may border on heresy, but I wonder if there is a way to dither the PPC clocks to spread out the emission? Maybe a cure worse than the disease! :-) Dave
Re: [casper] ROACH and ADC RFI tests
Thanks, John! On Sep 6, 2011, at 1:47 PM, John Ford wrote: Hi, John, That's very interesting. How does this compare with a laptop or other PC? Why was it tested with the lid off? Is that how it will be deployed? Laptops and other PCs are a different kettle of fish altogether. They have a wide range of emissions, and most of them have emission about 40 dB above the ITU limits at the distance of the lab here. This may border on heresy, but I wonder if there is a way to dither the PPC clocks to spread out the emission? Maybe a cure worse than the disease! :-) This is a ploy to fool the tests, since a spectrum analyser is sweeping, and measuring only one frequency at a time, so the average power measured in each frequency is less, but the total power in the clock is still the same. IMO! John Dave
