[USRP-users] USRPB210 master clock rate and RF front end bandwidth

Derek Kozel derek.kozel at ettus.com
Mon Oct 30 11:48:22 EDT 2017


Hi Wahhab,

It sounds like you are expecting a configuration which is not possible.

With an ADC sampling rate of 2 MS/s complex your application will receive
valid information about 2 MHz of bandwidth. Setting the analog bandwidth to
2 MHz or 56 MHz will not change this. In order to receive information about
all 56 MHz of bandwidth the ADC rate must also be at least 56 MS/s.

A good way of checking the configuration would be to visualize the
streaming sample data. There are many applications which will read the IQ
data file produced by your above command and display an FFT. GNU Radio is
one of the most common ones, but Matlab/Octave works too as does
Inspectrum, SDR#, baudline, and others.


As a final note, it is generally preferable to use a high master_clock_rate
and then use the USRP's FPGA to decimate to a lower rate. This gives you
the benefit of oversampling and faster responsiveness as most of the
digital logic and the transceiver run at the master clock rate.

Regards,
Derek

On Mon, Oct 30, 2017 at 1:20 PM, Wahhab Albazrqaoe via USRP-users <
usrp-users at lists.ettus.com> wrote:

> ​​I have USRPB210 and would like to set the bandwidth of the RF front to a
> high value, like 56MHz or 61.44MHz (which I think the max value supported
> by B210). At the same time, I would like to set the sampling rate of ADC to
> 2MHz. I used the following cmd to do so:
> ./rx_sample_to_file --args master_clock_rate 2MHz --bw=56MHz --freq=2410e6
>
> when I run the program, I got a message says that
> the sampling rate is 2.0000 MHz
> Actual Rx bandwidth is 56MHz
>
> These messages say show the configuration of USRPB210. However, I think
> this configuration is not real. How do I check it?
> I have a program (call it P) that monitors Bluetooth packets and there are
> two cases to check:
> Case1: --args master_clock_rate 2MHz --bw=2MHz, here we expect P to get j
> Bluetooth packets.
> Case2: --args master_clock_rate 2MHz --bw=56MHz, here we expect P to get
> (56/2=28) x j Bluetooth packets. That is, the number of packets is (28
> times j) as P monitors more Bluetooth channels.
>
> In reality, P got only j packet in Case2. This confirms that the RF front
> end (or something else in USRPB210) is not configured correctly as 56MHz.
>
> I did another check on USRPB210 to confirm. In particular, I used the
> following settings (let's call it Case3):  --args master_clock_rate 56MHz
> --bw=56MHz. In this case, P got (28 times j) Bluetooth packets, which
> confirms my checking procedure above.
>
> I appreciate if anyone could help me to configure USRPB210 just like Case2
> correctly.
>
> Wahhab Albaz​
>
>
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> USRP-users mailing list
> USRP-users at lists.ettus.com
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>
>
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