Hi all,

I know this is an old thread, but I wanted to report that me and my team
have been working in an RFI mitigation technique for ROACH2, based in
frequency domain adaptive filter. This requires a reference antenna no
measure the RFI in the environment, I understand that there have been FPGA
implementations of this before, but I've never seen an implementation and
results in CASPER hardware. Here is the paper for everyone interested:
https://arxiv.org/abs/1805.06376. We are currently trying to test the
filter in China's Five hundred meter Aperture Spherical Telescope (FAST),
and we expect to have results soon.

Thanks,

Franco

On Tue, Dec 12, 2017 at 9:55 PM, Dan Werthimer <d...@ssl.berkeley.edu>
wrote:

>
> hi xavier,
>
> it sounds like you are switching between two signal sources,
> one is a reference load with a very small signal level,
> and the other is a signal from the sky with strong RFI?
>
> if that's the case, can you turn up the signal level on your reference
> level?
> it would be best if the RMS is around 10 on a scale of -128 to +127
> for both signal sources.   (so that neither source saturates the adc,
> and neither source has too small a signal level where you degrade the SNR
> from finite quantization).
>
> if you are not switching between two sources,  and you have a very weak
> astronomical
> signal buried in RFI and noise, then that's fine - the weak astronomical
> signal can be much
> lower than a single bit on the ADC and you can recover it from integration
> in your spectrometer.
> just don't let your ADC saturate too often as that splatters power around
> the spectrum.
> (or if the ADC is saturating from impulsive RFI, then use one of the
> casper libraries that detects
> this saturation and replaces it with noise).
>
> best wishes,
>
> dan
>
>
>
>
> On Tue, Dec 12, 2017 at 4:36 PM, Xavier Bosch <bruixa.aburrid...@gmail.com
> > wrote:
>
>> Hi Bob,
>>
>> Thank you for your answer.
>> Yes, calibrating the 8-bit 5-GSPS ASIAA ADC is a must! I worked on that
>> some time ago.
>> I always make sure that the 4-cores OGP and IODELAYS calibration residual
>> error is within a acceptable range before starting any data acquisition.
>>
>> We also have checked the whole LNA chain linearity and it is fine, there
>> is no harmonic distortion. So, we narrowed down the problem to the fact
>> that we do not have enough dynamic range in the ADC to accommodate the RFI,
>> avoiding clipping, and simultaneously having enough bits (>2) when looking
>> to a clean reference load.
>>
>> Thank you again,
>> XB
>>
>>
>> On Mon, Dec 11, 2017 at 2:16 PM Wilson, Robert <rwil...@cfa.harvard.edu>
>> wrote:
>>
>>> Hi Xavier,
>>>
>>> One problem with the the 8-bit 5-GSPS ASIAA ADC board is that the ADC
>>> has four cores and if they are not exactly aligned, a strong RFI signal
>>> will be modulated by and mix with the periodic errors producing a number of
>>> artifacts.
>>>
>>> Bob Wilson
>>>
>>> On Thu, Dec 7, 2017 at 5:10 PM, Xavier Bosch <
>>> bruixa.aburrid...@gmail.com> wrote:
>>>
>>>> Hi CASPERites,
>>>>
>>>>
>>>>
>>>> We are developing a wideband spectrometer (~1.6 GHz ) in a band that
>>>> has a lot of RFI. Currently we are using the 8-bit 5-GSPS ASIAA ADC board
>>>> and the ROACH2, and the ADC resolution appears to be inadequate for our
>>>> extreme RFI environment.
>>>>
>>>>
>>>>
>>>> We would like to move over to a higher resolution ADC (12 to 14 bits),
>>>> probably with a JESD204B interface, and a Xilinx development kit. We are
>>>> considering something like this evaluation board KCU105
>>>> <https://www.xilinx.com/products/boards-and-kits/kcu105.html#hardware>and
>>>> something like FMC217
>>>> <https://www.vadatech.com/product.php?product=528&catid_prev=0&catid_now=0>
>>>> as a digitizer.
>>>>
>>>>
>>>> Has anyone been in a similar situation dealing with RFI?
>>>>
>>>> Has anyone ported CASPER library to Xilinx development kits and
>>>> JESD204B ADCs?
>>>>
>>>>
>>>> Thank you,
>>>>
>>>> XB
>>>>
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-- 
Franco Curotto
Estudiante de Ingeniería Civil Eléctrica
Facultad de Ciencias Físicas y Matemáticas
Universidad de Chile

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