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Re: Re: Can I shift center frequency twice with Xlating FIR

From: Phil Wiggum
Subject: Re: Re: Can I shift center frequency twice with Xlating FIR
Date: Fri, 9 Jul 2021 14:28:31 +0200

Hi Fabian!

Yes I Xlating and filter the Bw to 100K and then decimating to SampRate 100k to
be get a morefine details in the GUI Frequency.

I tested with a second Xlating in parallel and it worked perfect.

PS. Is there any mirroring of this list with a WEB gui?


> Hi Phil,
> I read your post like four times and could not figure out what you are
> doing and what you are trying to achieve. Where is your target signal
> originally located? At fc? Is fc = 100k? Why do you mix 100k down with
> the Frequency Xlating FIR and then define a different center frequency
> for your Frequency sink? An example graph would be helping.
> Nevertheless, it seems like you just want to shift the frequency around
> (i.e., mix the signal) and low pass filter it. You can do this as many
> times in parallel as you want. And maybe using the Low Pass Filter
> component will make things easier, as you don't have to define taps
> manually. Mixing can be done with a complex signal source combined with
> a multiplier or you use the Frequency Xlating FIR with [1] as taps. Note
> that a positive center frequency for the Frequency Xlating FIR will
> actually mix the signal down (negative frequency).
> Hope that helps a bit,
> Fabian
> Am 08.07.21 um 21:32 schrieb Phil Wiggum:
> > I Have this setup
> >
> > SDR(fc)
> >  -> 'Frequency Xlating FIR Filter' (Low pass, Center Freq: 100k)
> >   -> Resampler( 5M/100k)
> >    -> 'QT GUI Frequency Sink' (Center: fc+100k, Bw 100k)
> > And parallel with QT GUI FSink,
> >    -> 'Log Power FFT' -> Python (Peak detektor)
> >
> > My problem I have is the read out from 'Log Power FFT' starts at 'fc+100k'.
> > I would like it to start 'fc+50k'.
> > Can I use 'Frequency Xlating FIR Filter' again and lower my frequency
> > starting point?
> >
> > Like this parallel with QT GUI FSink,
> >    -> 'Frequency Xlating FIR Filter' (????)
> >     -> 'Log Power FFT' -> Python (Peak detektor)
> >
> > What kind on taps do I need if this is possible?
> >
> > /Phil
> >

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