Re: [Discuss-gnuradio] OFDM - real RF output vs. expected output

[Matt Ettus]

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 <address@hidden> 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
+49-171-3631223
address@hidden
http://www.bclog.de/



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