Hi Marcus,
On Wed, Oct 21, 2015 at 3:18 AM, Marcus Müller <[email protected]>
wrote:
> Hi Abhinav,
>
> which USRP are you using?
>
USRP N210
> I'm pretty sure none of our devices supports a 2kS/s sampling rate -- it's
> just far too low to get directly interpolated to a "usable" DAC/ADC rate.
> Especially those USRPs that can be equipped with RF frontends
> (daughterboards) that can operate at near-baseband (400kHz) shouldn't be
> able to work at such low rates. So: which daughterboard are you using?
>
> I see your point, I am using Basic TX/RX daughterboard.
I didn't notice the shell output but it makes sense now :
Terminal output:
The hardware does not support the requested TX sample rate:
Target sample rate: 0.001000 MSps
Actual sample rate: 0.195312 MSps
-- Tune Request: 0.400000 MHz
-- The RF LO does not support the requested frequency:
-- Requested LO Frequency: 0.400000 MHz
-- RF LO Result: 0.000000 MHz
-- Attempted to use the DSP to reach the requested frequency:
-- Desired DSP Frequency: 0.400000 MHz
-- DSP Result: 0.400000 MHz
-- Successfully tuned to 0.400000 MHz
Basically, the minimum sampling rate is 196 Ksamples/sec
Hence, UHD should have told you that you can't use that sampling rate, and
> a higher sampling rate was automatically selected, inherently
> frequency-"stretching" the signal by the ratio of (actual rate/2kHz).
>
> You should heed Sylvain's advice. Just oversample your signal by using an
> interpolating FIR filter to something that the USRP can happily work with.
>
> So, here is what I am not clear about- I should use 196 KHz as sampling
rate ?
So, the minimum BW of my signal will 196/2 =98KHz, and that is the best I
can do with this equipment, right ?
> Best regards,
> Marcus
>
> On 21.10.2015 08:49, abhinav narain wrote:
>
> Hi,
> I am transmitting using the flowgraph: vector src-> FIR interpolator (with
> RRC filter as below) -> MultiplyConst -> USRP Block
>
> FIR filter - firdes.root_raised_cosine(32, samp_rate, sps, 0.55,
> int(11*sps*32)), with
> center freq= 400kHz
> samp_rate= 1k
>
> I am listening using other USRP with
> center freq= 400kHz
> samp_rate= 2k
>
>
> You can see the spectrogram at the receiver. I want to do narrowband(1
> kHz) transmission hence I am keeping the sampling freq at transmitter at 1k.
>
> While I increase the signal amplitude(using MultiplyConst block with
> slider), I see there is more and more spillage of energy in the neighboring
> frequencies!
>
> Is there a way to remove that spillage from the transmitter and have a
> cleaner transmitter ?
> If not, how can I atleast mitigate it to the minimum ? is there something
> I can do with RRC filter parameter or any other way ?
>
> In the figure: 1 - when amplitude is large; 2 - when amplitude is turned
> down
>
> Thanks,
> Abhinav
>
>
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