> On May 9, 2018, at 4:07 PM, Marcus D. Leech via USRP-users
> <usrp-users@lists.ettus.com> wrote:
>
> On 05/09/2018 06:53 PM, Jacob Knoles via USRP-users wrote:
>> Hello All,
>>
>> I am trying to generate OFDM signals of various bandwidths using the X300
>> (UBX-160), particularly 20/40/80 and 160 MHz bandwidths.
>> I have used the gnuradio ofdm_tx.grc example file to generate a data file
>> which I then feed into the USRP an monitor on a spectrum analyzer.
>>
>> To quickly note, I do not care about the data being transferred, it will not
>> be received or demodulated in any way and is simply an interfering signal.
>>
>> At this time I can produce a 20 MHz wide OFDM signal as well as a 100 MHz
>> wide signal (?) but the 40/80 MHz signals are rounded and look more like an
>> 802.11b signal.
>>
>> I have noted a message from the X300 that the requested sample rates (40/80
>> MS respectively) cannot be achieved due to the 200/x ratio being odd.
>>
>> So my question is this, how do I decouple the USRP's sample rate with the
>> bandwidth of the signal I am trying to produce?
>> To put it another way, I produce a data file at 40 MS/s rate then run it on
>> the X300 at 100 MS/s and I get a 100 MHz wide signal instead of the 40 MHz I
>> want.
>>
>> Thanks for the help.
>> -----------------------------
>> Jacob Knoles
>>
> You would need to interpolate it up to the desired rate. UHD has no way of
> knowing that your samples represent data sampled at 40Msps, so when you
> pull it out of your file at 100Msps, it will get presented as if it were
> 100Msps data.
>
> You'll need to use some DSP code, or Gnu Radio to up-sample your sample file.
>
….or perhaps generate it off line using a non 2^n Fourier transform size that
targets the USRP sample rate…for example instead of 64 bins @ 40MHz, 80 bins @
50MHz,
With zero data in the extra outlying bins (as you would have anyway in other
bins). Might get interesting getting high bitrates out of a file, but equally,
high bitrate M:N sample rate conversion will also be tricky for CPU
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