|Subject:||Re: [Discuss-gnuradio] How to minimize Spillage of energy in neighboring frequencies while transmission|
|Date:||Wed, 21 Oct 2015 11:37:10 -0700|
which USRP are you using?
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?
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.
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)), withcenter freq= 400kHzsamp_rate= 1k
I am listening using other USRP withcenter freq= 400kHzsamp_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
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