Hi,
the simple GRC in the attachment creates lots of underflows on our E100
(“U” on console)
and dropouts when looking at the spectrum.
Is this as expected or how can this overload of the embedded Linux be
avoided?
Thanks,
Ralf
On 29/06/2011 9:11 AM, Ralf wrote:
Ralf
Well, for one, 60Khz isn’t a proper divisor of the 128MHz sample rate of
the DAC, which means it can’t be properly interpolated.
The minimum sample rate that you can deliver to the USRP-E100 is
128MHz/512 = 250kHz, so you’ll have to interpolate your
data stream up to 250kHz prior to “presentation” to the UHD sink
block.
Am 29.06.2011 16:34, schrieb Marcus D. Leech:
Thanks,
Ralf
Well, for one, 60Khz isn’t a proper divisor of the 128MHz sample rate
of the DAC, which means it can’t be properly interpolated.The minimum sample rate that you can deliver to the USRP-E100 is
128MHz/512 = 250kHz, so you’ll have to interpolate your
data stream up to 250kHz prior to “presentation” to the UHD sink block.
Hi Marcus, thanks for your reply.
That is very important for us to understand. How is the divider 512
determined? It is in the FPGA I suppose.
Where can read more about the FPGA besides this small text?
http://www.gnu.org/software/gnuradio/doc/exploring-gnuradio.html#fpga
Can we only put proper divisors of 128MHz in terms of datarate into the
UHD sink even above 250kHz?
Actually we need to put ~10kbit/s of data onto a ~400kHz carrier. Is the
GRC repeater the right functionality
to interpolate the small datarate as shown in the attached setup?
Regards,
Ralf
On 06/30/2011 05:27 AM, Ralf wrote:
Hi Marcus, thanks for your reply.
That is very important for us to understand. How is the divider 512
determined? It is in the FPGA I suppose.
Where can read more about the FPGA besides this small text?
http://www.gnu.org/software/gnuradio/doc/exploring-gnuradio.html#fpga
The FPGA supports a maximum interpolation ratio of 512. Interpolation
ratios must be even.Can we only put proper divisors of 128MHz in terms of datarate into
the UHD sink even above 250kHz?
Yup. Only bandwidths that result in an even interpolation ratio from
the 128MHz DAC sample
rate can be used.
Actually we need to put ~10kbit/s of data onto a ~400kHz carrier. Is
the GRC repeater the right functionality
to interpolate the small datarate as shown in the attached setup?
Normally, if you need to use a “weird” sample rate, you’d use something
like the fractional interpolator
block just before you send the stream to the UHD sink. Do you mean a
carrier that is 400kHz in
bandwidth, or a carrier at 400kHz center frequency? The center
frequency isn’t really relevant
to this discussion, but the bandwidth is.
–
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
Am 30.06.2011 um 11:27 schrieb Ralf:
Ralf
http://www.gnu.org/software/gnuradio/doc/exploring-gnuradio.html#fpgaCan we only put proper divisors of 128MHz in terms of datarate into the UHD sink
even above 250kHz?Actually we need to put ~10kbit/s of data onto a ~400kHz carrier. Is the GRC
repeater the right functionality
to interpolate the small datarate as shown in the attached setup?Regards,
Ralf
There is a collection of lots of internal details of the USRP1 under
www.gnuradio.org/redmine/attachments/129/USRP_Documentation.pdf
They might also apply to the operation of the E100’s FPGA logic.
You can also look at the source code directly
http://ettus-apps.sourcerepo.com/redmine/ettus/projects/uhd/repository/revisions/master/show/fpga
Regards,
Matthias