# Problem with ofdm bandwidth and sampling rate **URL:** \ **Category:** GNU Radio\ **Created:** [June 3, 2015, 12:58pm UTC](https://www.ruby-forum.com/t/problem-with-ofdm-bandwidth-and-sampling-rate/242187 "2015-06-03T12:58:36Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![Detlef\_R](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/58f4c7/32.png) [@Detlef\_R](https://www.ruby-forum.com/u/Detlef_R)\ **Post date:** [June 3, 2015, 12:58pm UTC](https://www.ruby-forum.com/t/problem-with-ofdm-bandwidth-and-sampling-rate/242187/1 "2015-06-03T12:58:36Z")
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**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\ **Post date:** [June 3, 2015, 1:58pm UTC](https://www.ruby-forum.com/t/problem-with-ofdm-bandwidth-and-sampling-rate/242187/2 "2015-06-03T13:58:47Z")
Hi Alphonso, I implemented a transmitter for the DRM(30) standard in GNU Radio and published it on github ([GitHub - kit-cel/gr-drm: DRM transmitter using GNU Radio · GitHub](https://github.com/kit-cel/gr-drm)). To (partly) answer your questions: 1. DRM only accepts specific audio sample rates, make sure to read the standard documents carefully. 2. Mixing is usually done by the USRP. You as the user only deal with the complex baseband centered around DC. 12 kHz would also be a VERY low carrier frequency, short-wave radio usually uses frequencies between 3 and 30 MHz. –Felix On 03.06.2015 12:57, [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > everything works fine but there is a problem with the spectrum of this > should i use a resampler block because there is a problem with > nyquist? how can i handle this problem? > 2) the same problem goes with the output. if i mix up the ofdm signal > to a carrier frequency (for example 12khz) how can i handle this? > there is also a problem with nyquist. > thanks in advance! > alphonso – Karlsruhe Institute of Technology (KIT) Communications Engineering Lab (CEL) Felix W., M. Sc. Research Associate Kaiserstra??e 12 Building 05.01 76131 Karlsruhe Phone: +49 721 608-46276 Fax: +49 721 608-46071 E-Mail: [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) www.cel.kit.edu KIT – University of the State of Baden-W??rttemberg and National Laboratory of the Helmholtz Association ---
**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\ **Post date:** [June 4, 2015, 8:21am UTC](https://www.ruby-forum.com/t/problem-with-ofdm-bandwidth-and-sampling-rate/242187/3 "2015-06-04T08:21:45Z")
Hi, please remember to always reply to the list. If you mix your baseband signal in a way that no part of your spectrum includes negative frequencies BEFORE doing the complex-to-real conversion, this should work. At least from a signal processing perspective. I never used my soundcard as a transmitter, so I can’t really help you with that. –Felix On 03.06.2015 15:02, [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > were problems with licensing and changed or removed functions in > 2) i don’t have an USRP. i want to use a sound card to get my signal > Hi Alphonso, > low carrier frequency, short-wave radio usually uses frequencies > standard. so my first try was to implement the transmitter with > with the parameters above and the wish of a bandwidth of 10khz (to > this? there is also a problem with nyquist. > Kaiserstra??e 12 > National Laboratory of the Helmholtz Association – Karlsruhe Institute of Technology (KIT) Communications Engineering Lab (CEL) Felix W., M. Sc. Research Associate Kaiserstra??e 12 Building 05.01 76131 Karlsruhe Phone: +49 721 608-46276 Fax: +49 721 608-46071 E-Mail: [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) www.cel.kit.edu KIT – University of the State of Baden-W??rttemberg and National Laboratory of the Helmholtz Association ---
**Author:** ![unknown](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/u/4bbf92/32.png) [@unknown](https://www.ruby-forum.com/u/unknown)\ **Post date:** [June 4, 2015, 8:59am UTC](https://www.ruby-forum.com/t/problem-with-ofdm-bandwidth-and-sampling-rate/242187/4 "2015-06-04T08:59:44Z")
I’d also like to point out that you should use an oscilloscope to verify that a sine with a 17 kHz frequency has the same peak-to-peak voltage as one with the same digital amplitude at 7 kHz – sound cards do have nice DACs (bitdepth-wise), but the analog filtering that you must do after DAC’ing tends to be implemented in a one-stage passive way (at least for the cheap consumer-grade sound cards I’ve encountered), which will not make your spectrum pretty. However, you said there’s an existing Matlab implementation – was the “Soundcard channel” measured with respect to frequency selectivity? Best regards, Marcus