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[Discuss-gnuradio] How to minimize Spillage of energy in neighboring fre

From: abhinav narain
Subject: [Discuss-gnuradio] How to minimize Spillage of energy in neighboring frequencies while transmission
Date: Tue, 20 Oct 2015 23:49:50 -0700

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


Attachment: problem_spillover.PNG
Description: PNG image

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