On 18/02/2025 21:45, Brendan Horsfield wrote:
Point taken. At this stage we are mainly interested in straight IQ
recording & playback with minimal processing. However, in the future
it would be desirable to be able to display a real-time spectrum trace
& waterfall plot during recording/playback, using GNU Radio or
something like it.
As you suggest, I am assuming our host machine will need a dual-10Gbe
adaptor card and a high-spec CPU, memory, SSD etc. This is a complex
procurement exercise all by itself.
My understanding (and I haven't played with them) is that NVME SSDs are
among the fastest. Performance up to a few GByte/Sec
on write is possible, although I don't know if it can be sustained
at those rates, or whether it's "bursty".
I've been able to produce "real-time" spectral displays on 10yo
dual-Xeon hardware at 100Msps, but only using the
kind of "stuttered" display approach that Gnu Radio FFT displays
often use, where most of the data is discarded. Often,
that's all that's needed to show a quick summary of the spectrum.
On your other question, about transition bandwidth, I don't have a
direct answer, but on an N310 I measured the roll-off
as a fraction of the overall bandwidth, and it is about 12.5%. That
doesn't necessarily translate to the X310, but the
DDC implementation is of the same generation.
On Wed, 19 Feb 2025 at 10:58, Marcus D. Leech
<patchvonbr...@gmail.com> wrote:
On 18/02/2025 19:26, Brendan Horsfield wrote:
I thought your name sounded familiar! 🙂
Overall the X310+UBX-160 appears to be a good fit to our
requirements. My original question was really about ensuring
that our host PC & network interface have sufficient bandwidth to
ingest the IQ data from a pair of UBX-160s. It would be nice
(although not essential) if we could run one channel at 100 Msps,
and the other at 200 Msps, to reduce the bandwidth requirements
on the backend hardware.
You'd need to have separate streamers to support two different
sample rates, and two 10Gbe interfaces.
But in terms of "what kind of PC hardware do I need?". There's no
closed-form answer to that question. There's no
handy-dandy "engineering worksheet" that tells you how much
"grunt" you need for different DSP "flows" at
a given sample-rate--so very much depends on what you're doing,
and how you're doing it. Generally, as you scale up
in sample-rate, you have to scale up in:
o CPU base clock rate
o Memory bandwidth
o Number of CPUs
On Wed, 19 Feb 2025 at 10:17, Marcus D. Leech
<patchvonbr...@gmail.com> wrote:
On 18/02/2025 19:13, Brendan Horsfield wrote:
Thanks for the suggestion about the noise source -- that's
what I would normally do. Unfortunately I haven't actually
purchased the hardware yet -- I was hoping to clarify this
issue before raising a purchase order.
Perhaps I should follow this up with one of the application
engineers at NI? They might have access to an X310+UBX-160
system that they can use to answer my question directly.
Thanks again for your help in this matter.
Regards,
Brendan.
I actually do work for NI on USRP devices (on a very very
very part-time basis). My X310 is currently elsewhere, and
not populated
with a UBX-160.
On Wed, 19 Feb 2025 at 09:55, Marcus D. Leech
<patchvonbr...@gmail.com> wrote:
On 18/02/2025 18:45, Brendan Horsfield wrote:
Yes, I assumed that was the case. However, it is not
clear from the X300 documentation how sharp those
filters are. Can you tell me how wide the transition
band is at the lower sample rates?
To give you some context, I would like to use an X300
(or X310) with a UBX-160 daughterboard to digitise the
entire 2.4 GHz Wi-Fi band, which is 83.5 MHz wide.
Ideally I would like to use a sample rate of 100 Msps
to minimise the data rate between the USRP and the host
PC. However, before I do this I need to be certain
that the usable bandwidth at this sample rate will be
greater than 83.5 MHz. Is this information documented
somewhere?
It somewhat depends on the decimation. If the
decimation has a factor of two or 4, the edge roll-off
is fairly sharp. Otherwise,
there's a half-band filter in-place that causes a
less-desirable pass-band.
But I don't know, precisely, what the transition band is
in the "nicer" filter shapes.
If you have an X310+UBX-160, you can always just use a
noise source, and measure it yourself to see if it's
appropriate for
your application.
On Tue, 18 Feb 2025 at 23:11, Marcus D Leech
<patchvonbr...@gmail.com> wrote:
There will always be some edge roll off. Decimation
includes filtering and those filters cannot be
infinitely steep.
Sent from my iPhone
> On Feb 18, 2025, at 2:12 AM, Brendan Horsfield
<brendan.horsfi...@vectalabs.com> wrote:
>
>
> Hi All,
>
> I have a question about the usable bandwidth of
the X300 USRP / UBX-160 daughterboard combo at
sampling rates below 200 Msps:
>
> As I understand it, the UBX-160 receiver has an
analog (hardware) filter before the ADC that limits
the usable bandwidth to 160 MHz, while the ADC runs
at 200 Msps. Therefore the usable bandwidth is
around 80% of the sample rate.
>
> My question is: What is the usable bandwidth at
lower sampling rates? Does the 80% factor always
apply?
>
> For example, if I set the decimation factor to 4,
so that my sampling rate is 50 Msps, does this mean
that the usable bandwidth will be 40 MHz?
>
> Thanks & Regards,
> Brendan.
>
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