Aah, OK, in fact it is odd. So I will modify my parameters and try again... Just got confused that theoretical and practical results were so different :)
Meanwhile I had a look into the WBX schematics, fixed filters before/after ADC/DAC, as expected. Ralph. From: Matt Ettus [mailto:m...@ettus.com] Sent: Thursday, February 14, 2013 7:51 AM To: Ralph A. Schmid, dk5ras Cc: GNURadio Subject: Re: [Discuss-gnuradio] OFDM - real RF output vs. expected output You are probably using an odd interpolation ratio. You need to use an even rate in order to get a flat passband. The WBX does not have adjustable filtering. Matt On Wed, Feb 13, 2013 at 10:42 PM, Ralph A. Schmid, dk5ras <ra...@schmid.xxx> wrote: Hi, I use an USRP1 together with gnuradio/GRC and would like to transmit an OFDM signal, abt. 1 MHz bandwidth at 433 MHz. The FFT display block within GRC shows the power mask as expected, a flat line over the bandwidth, and steep drops at both ends. What a real spectrum analyzer at the output shows is something totally different, like a Gaussian distribution of the emitted energy, with highest amplitude in the center, bandwidth as configured, but the amplitude is dropping continuously towards the ends for about 70 dB or so. Adjusting the channel bandwidth in the sink block has no influence, maybe the WBX anyway does not support adjustable filtering?! Even the simplest possible setup, like random source, OFDM modulator and URSP, shows this behavior. What am I doing wrong? Btw., the spectrum analyzer is a professional device and out of any doubt :) LTE, DAB and DVB-T is shown as expected. Ralph. -- Ralph A. Schmid Mondstr. 10 90762 Fürth <tel:%2B49-171-3631223> +49-171-3631223 <mailto:ra...@schmid.xxx> ra...@schmid.xxx <http://www.bclog.de/> http://www.bclog.de/ _______________________________________________ Discuss-gnuradio mailing list <mailto:Discuss-gnuradio@gnu.org> Discuss-gnuradio@gnu.org <https://lists.gnu.org/mailman/listinfo/discuss-gnuradio> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
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