Re: Help to remove DC offset

[Arhum Ahmad]

Yes, in that case, could we reduce the strength of DC so that it won't interfere while detecting the signal's frequency (on the run)?

On Thu, Feb 15, 2024 at 4:40 PM Marcus Müller <marcus.mueller@ettus.com> wrote:

Hey,

can we keep this on the mailing list, please?

But logically, if you have signal of interest where your DC is, then a high-pass filter is not an option.

Best,
Marcus

On 15.02.24 10:55, Arhum Ahmad wrote:

Hey Marcus,

I am using it to find the signal frequency present in the given band. However, in some cases, I found DC is more dominant, and I am unable to detect the presence of the signal and its frequency.

If I use the high pass filter to remove the DC offset, how should I calculate the cut-off? Considering the fact that there might be a signal at the center.

On Sun, Feb 11, 2024 at 10:52 PM Marcus Müller <marcus.mueller@ettus.com> wrote:

Hi Arhum,

some limited amount of DC offset is sadly to be expected from any direct conversion architecture (that's a result of LO leakage as well as systematic DC offset).

Since DC is the lowest of all possible frequencies, a high-pass filter can be used to eliminate it. The design of that filter depends on what you want to do with the signal afterwards – for example, for some communication system signals, the DC offset literally doesn't matter.

Another option is, if your signal is sufficiently more narrowband than the Nyquist bandwidth dictated by your receiver's sampling rate, to "offset-tune"; i.e., to put your signal of interest to the positive (or negative) side of your LO frequency, and then digitally shift the signal of interest to actual baseband and filter.

The USRPs bring that functionality out of the box, integrated into the device's digital part, so you can just deal with the signal decimated to the bandwidth you need in your computer. I'm not sure, but I don't think the HackRF allows for that. You'd have to offset-tune within your full sampling rate, and in GNU Radio use something like the "freq. X-lating FIR filter" to get the part of the spectrum you want.

Best regards,
Marcus

On 10.02.24 12:02, Arhum Ahmad wrote:

Hey all,

I'm currently working on frequency sensing using the HackRF SDR. However, when I calculate the FFT, I encounter a DC offset that's higher than the actual signal strength itself. This offset is interfering with my ability to detect the intended output accurately. Could you please assist me in understanding how to remove this DC offset?

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Thanks and Regards

Arhum Ahmad
Ph.D. Scholar, Electrical Engineering Department, IIT Ropar

+91-7974897279 | arhum.19eez0005@iitrpr.ac.in

Lab No. 323, Communication Research Lab, J.C.Bose Building

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--

Thanks and Regards

Arhum Ahmad
Ph.D. Scholar, Electrical Engineering Department, IIT Ropar

+91-7974897279 | arhum.19eez0005@iitrpr.ac.in

Lab No. 323, Communication Research Lab, J.C.Bose Building

CONFIDENTIALITY NOTICE: The contents of this email message and any attachments are intended solely for the addressee(s) and may contain confidential and/or privileged information and may be legally protected from disclosure. If you are not the intended recipient of this message or their agent, or if this message has been addressed to you in error, please immediately alert the sender by reply email and then delete this message and any attachments. If you are not the intended recipient, you are hereby notified that any use, dissemination, copying, or storage of this message or its attachments is strictly prohibited.

--

Thanks and Regards

Arhum Ahmad
Ph.D. Scholar, Electrical Engineering Department, IIT Ropar

+91-7974897279 | arhum.19eez0005@iitrpr.ac.in

Lab No. 323, Communication Research Lab, J.C.Bose Building

CONFIDENTIALITY NOTICE: The contents of this email message and any attachments are intended solely for the addressee(s) and may contain confidential and/or privileged information and may be legally protected from disclosure. If you are not the intended recipient of this message or their agent, or if this message has been addressed to you in error, please immediately alert the sender by reply email and then delete this message and any attachments. If you are not the intended recipient, you are hereby notified that any use, dissemination, copying, or storage of this message or its attachments is strictly prohibited.