[Discuss-gnuradio] Strange side-band when transmitting using WBX on USRP1

[Drew Read]

Hi All,

We're having some problems with transmitting using the WBX board on a
USRP1 (not an old one).
We have a flow graph with a NULL source going into a NBFM, then
through a multiply_const and into the USRP.
At low frequencies (100MHz) the signal looks ok, but when we get up
passed 500MHz we can see/hear that what should be an unmodulated
carrier also has a single side-band (and is audible as a tone when
demodulated) . And by increasing the const in the multiply_const, we
can see our wanted signal getting stronger while the side-band remains
there at a constant level.

We've had a play with manually adjusting the DC offset of the USRP
sink, which seems to change the size of the side-band a bit, but we
don't really know what to do with that.

We've tried several USRPS and several WBX boards and seen the same
problem on all of them.
We don't see it on the USRP2.
We don't see it with the flex400 board.

This picture http://tinyurl.com/27w5s8n shows the side-band on the
left and the wanted signal on the right.
The grc file is also attached.

Any help you can offer would be greatly appreciated thanks!

Drew

--
Andrew Read +64 (03) 357 0787
Test Analyst
Design Verification and Validation Team
Tait Electronics Ltd

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weird-sideband.grc
Description: Binary data