Downsampling a 20MHz AM signal to 1MHz for ZYNQ processing

[ahad512]

I am trying to downsample a 20MHz signal to a 1MHz signal. while doing this signal the low-intensity signal is skipped. Another issue arising due to Downsampling is Aliasing. I have to demodulate the downsampled signal. On demodulating the single channel, there is audio from another channel what measurements should be taken.

 

[KlausST]

Hi,

Explain how exactly you "tried" it.
What exactly is the sampling frequency? How is it generated? Is it aligned somehow to the carrier frequency?

What does this mean: " the low intensity signal is skipped"?
And: Is this good or bad?

Aliasing: Generally you need to get rid of the "other channel" before sampling.
All frequencies in the source signal get mirrored down to fs/2 bandwidth. So your filter in the source side needs to suppress all frequencies outside this band.

On the digital side you may use additional filters to suppress signal within this band.

Klaus

 

[kaz1]

I am trying to downsample a 20MHz signal to a 1MHz signal. while doing this signal the low-intensity signal is skipped. Another issue arising due to Downsampling is Aliasing. I have to demodulate the downsampled signal. On demodulating the single channel, there is audio from another channel what measurements should be taken.

I guess you mean downsampling from 20Msps to 1Msps.
Use a filter cutting off at 0.5MHz or better then decimate.
passband ripple to be as flat as possible for your case.

 

[ahad512]

I guess you mean downsampling from 20Msps to 1Msps.
Use a filter cutting off at 0.5MHz or better then decimate.
passband ripple to be as flat as possible for your case.

can you please elaborate in detail I am using Simulink for this purpose

Hi,

Explain how exactly you "tried" it.
What exactly is the sampling frequency? How is it generated? Is it aligned somehow to the carrier frequency?

What does this mean: " the low intensity signal is skipped"?
And: Is this good or bad?

Aliasing: Generally you need to get rid of the "other channel" before sampling.
All frequencies in the source signal get mirrored down to fs/2 bandwidth. So your filter in the source side needs to suppress all frequencies outside this band.

On the digital side you may use additional filters to suppress signal within this band.

Klaus

I have tried it using the downsampling block in Simulink
No, I need that low-intensity signal
I have multiple data channels in the 20MHz band while a single channel bandwidth is not more than 12k

 

[kaz1]

can you please elaborate in detail I am using Simulink for this purpose

Your signal of interest is from dc up to half of 1MHz judging from your downsampling plan.
Thus for downsampling correctly you need a decimation filter (or chain of filters) with final cutoff of 0.5MHz. This will remove unwanted signals and aliasing. so you will be left with your signal of interest after decimation.

 

[FvM]

I read in the description that the Simulink Downsample block decreases the sampling rate by deleting samples. No appropriate method without using a low pass filter in front of the decimator because it involves aliasing and reduction of signal-to-noise ratio. I rather suggest to use a regular FIR decimation filter.