Hi Andreas,
which USRP is this about? My guess is the X310, and you're using the BasicTX
daughterboard. Is that correct?
To talk about features of the DSP architecture, it's also (very) relevant to know which
version of UHD we're talking about!
I have tried to add skip_duc=1 which is mentioned in some of the documentation, but the output spectrum does
not change.
That's true, I only find a single seemingly orphaned code mention of skip_duc... but it
was only mention (if I remember correctly) in the documentation of the N3xx, so that would
conflict with my X3xx guess...
Is this command outdated or not supported? I wonder since the HG FPGA image has listed that the routing
between DUC and radio are “static”.
This depends on the UHD version; generally, RFNoC will allow you to feed full-rate signal
into the radio frontend. The "newer" the UHD, the more flexible it gets, essentially.
have noticed that I get something closer to what I want if I choose an odd interpolation
order, by setting master_clock_rate to 190 MHz instead of 200MHz.
Uh! That now completely clashes with my guess, because the X310 doesn't support 190 MHz
MCR at all, I thought.
But yes, if you use an odd interpolation on any third series USRP, you get "less good"
spectrum, because none of the relatively good half-band filters can be used, and the
adjustable CIC filter needs to do it all, leading to sidelobes, which in turn lead to more
squarishness.
Best regards,
Marcus
On 24.11.21 11:40, Andreas.Bertheussen--- via USRP-users wrote:
Hi,
I’d like to create (imitate) the sinc(f/fs) spectrum that would be generated from an
unfiltered zero-order hold DAC output, clocked at 10 Mhz. Main characteristics are a
peak around center frequency, rolling off to nulls at +- 10 MHz around the center frequency.
The IF signal is a random BPSK sequence.
When I stream the BPSK sequence at 10 MHz , I get a flat spectrum between +- 5MHz since
the DUC is doing its job in upsampling to 200MHz DAC rate.
I have tried to add skip_duc=1 which is mentioned in some of the documentation, but the
output spectrum does not change. Is this command outdated or not supported? I wonder
since the HG FPGA image has listed that the routing between DUC and radio are “static”.
I have noticed that I get something closer to what I want if I choose an odd
interpolation order, by setting master_clock_rate to 190 MHz instead of 200MHz. The
upsampling ratio becomes 190MHz/10MHz = 19, which is odd, and I get some warnings about
half-band filters and CIC roll-of in the console.
In this mode, what does the DUC do to the signal? Is it equivalent to bypassing
the DUC?
How do I best avoid any effects introduced by DUC?
Regards,
Andreas.
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