Re: [Discuss-gnuradio] How to minimize Spillage of energy in neighboring frequencies while transmission

[Marcus Müller]

What is alias filtering ? I have hear about anti-alias filters. Apologies as I am a CS student

but interested in radios and hence working on the project. I might be missing something 

obvious.

It's the same.
As mentioned, your hardware shouldn't be working at 2kS/s at all -- you should definitely read the full textual output of your program

You mean at 400k center freq, I have a sample_rate of 400k X 10 = 4M ?

Isn't this going to increase my transmisson BW ? 

No, that's not oversampling.
Oversampling is taking your signal as it is now, i.e. calculated for a digital-to-analog conversion rate of 2kSamples per second, and padding it with N-1 zeros after each sample, so that you have N*2kS/s afterwards. Because that N-1 introduces aliases, you have to filter the result, so that the N*2kHz of Nyquist bandwidth actually only contain signal in the central 2kHz. The result is the same signal, just at a higher sampling rate.

Best regards,
Marcus

On 10/21/2015 08:42 PM, abhinav narain wrote:

Hi Sylvain,

 

> 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.

That sentence is just wrong. It's actually quite the opposite.

By keeping the sample rate at the transmitter at 1k, you're basically
leaving all the alias filtering to the hardware and it's just not that
good.

What is alias filtering ? I have hear about anti-alias filters. Apologies as I am a CS student

but interested in radios and hence working on the project. I might be missing something 

obvious.

 

You would be much better off oversampling the TX by like 10 and then
do digital filtering to make sure you filter out anything in the
higher freq.

You mean at 400k center freq, I have a sample_rate of 400k X 10 = 4M ?

Isn't this going to increase my transmisson BW ? 

Sure, I can do that with low pass filter at the receiver, but I don't want a massive frequency 

spectrum signature on the channel itself. My priority/requirement is to keep my transmission detectability

in the spectrum as low as possible.

Looking for your comments,

Abhinav

Cheers,

   Sylvain

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