Hi Tom,
The peak in the middle of your received spectrum is likely due to a DC
offset in your RF chain. Keep in mind the LF boards are DC-coupled.
Are you using multi_usrp APIs to tune to 12 kHz, or are you doing that
frequency shifting in your software?
If you move the 12 kHz signal to baseband, and then do lowpass filtering,
the DC component will be filtered out.
--M
On Thu, Feb 27, 2025 at 6:41 AM Q W via USRP-users <
usrp-users@lists.ettus.com> wrote:
Hi there,
I am using two USRPs to transmit and receive signals. The transmitter is a
USRP N210 with an LFTX daughterboard. The receiver is a USRP X310 with an
LFRX daughterboard. The transmitter and receiver are connected via a cable
with a 30-dB attenuator. The carrier frequency at the transmitter is 12 kHz.
The problem I am stuck into is the received spectrum (See the diagram
below.). The spectrum consists of a positive and a negative frequency
components, when the carrier frequency configured at the receiver is 0
Hz. This can be expected as the transmitted signal is real and LFRX doesn't
have analog frequency mixers. I am confused about the peak in the middle of
the two frequency components which is now located at DC. I thought it was
LO leakage, so tried using different carrier frequencies at the receiver.
However, this peak will always appear at whatever the frequency is and will
be always in the middle of the two components. I feel it might not be the
LO leakage, but something unknown to me. I hope to filter it out using
some DSP method.
[image: Inline image]
For reference, the spectrum of the baseband signal in the transmitter is
shown below.
[image: Inline image]
Kind regards,
Tom
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Hi Tom,
The peak in the middle of your received spectrum is likely due to a DC
offset in your RF chain. Keep in mind the LF boards are DC-coupled.
Are you using multi_usrp APIs to tune to 12 kHz, or are you doing that
frequency shifting in your software?
If you move the 12 kHz signal to baseband, and then do lowpass filtering,
the DC component will be filtered out.
--M
On Thu, Feb 27, 2025 at 6:41 AM Q W via USRP-users <
usrp-users@lists.ettus.com> wrote:
> Hi there,
>
> I am using two USRPs to transmit and receive signals. The transmitter is a
> USRP N210 with an LFTX daughterboard. The receiver is a USRP X310 with an
> LFRX daughterboard. The transmitter and receiver are connected via a cable
> with a 30-dB attenuator. The carrier frequency at the transmitter is 12 kHz.
>
> The problem I am stuck into is the received spectrum (See the diagram
> below.). The spectrum consists of a positive and a negative frequency
> components, when the carrier frequency configured at the receiver is 0
> Hz. This can be expected as the transmitted signal is real and LFRX doesn't
> have analog frequency mixers. I am confused about the peak in the middle of
> the two frequency components which is now located at DC. I thought it was
> LO leakage, so tried using different carrier frequencies at the receiver.
> However, this peak will always appear at whatever the frequency is and will
> be always in the middle of the two components. I feel it might not be the
> LO leakage, but something unknown to me. I hope to filter it out using
> some DSP method.
> [image: Inline image]
>
> For reference, the spectrum of the baseband signal in the transmitter is
> shown below.
> [image: Inline image]
>
> Kind regards,
> Tom
> _______________________________________________
> USRP-users mailing list -- usrp-users@lists.ettus.com
> To unsubscribe send an email to usrp-users-leave@lists.ettus.com
>
