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Re: Can I shift center frequency twice with Xlating FIR

From: Fabian Schwartau
Subject: Re: Can I shift center frequency twice with Xlating FIR
Date: Fri, 9 Jul 2021 14:35:45 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

You are welcome, glad I could help :)
The list is mirrored here:
https://lists.gnu.org/archive/html/discuss-gnuradio/ Read-only, of course.


Am 09.07.21 um 14:28 schrieb Phil Wiggum:
> 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?
> /Thanks
> Phil
>> 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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